<< Previous article

A cometary origin for martian atmospheric methane

M. Fries1,

1NASA Johnson Space Center, Astromaterials Research and Exploration Science (ARES), Houston, TX 77059, USA

A. Christou2,

2Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland

D. Archer3,

3Jacobs, NASA Johnson Space Center, Houston, TX 77059, USA

P. Conrad4,

4NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

W. Cooke5,

5NASA Marshall Space Flight Center, Huntsville, AL 35812, USA

J. Eigenbrode4,

5NASA Marshall Space Flight Center, Huntsville, AL 35812, USA

I.L. ten Kate6,

6Department of Earth Sciences, Utrecht University, Netherlands

M. Matney1,

1NASA Johnson Space Center, Astromaterials Research and Exploration Science (ARES), Houston, TX 77059, USA

P. Niles1,

1NASA Johnson Space Center, Astromaterials Research and Exploration Science (ARES), Houston, TX 77059, USA

M. Sykes7,

7Planetary Science Institute, Tucson, AZ 85719-2395, USA

A. Steele8,

8Geophysical Laboratory, Carnegie Institution for Science, Washington DC, USA

A. Treiman9

9Lunar and Planetary Institute, Houston, TX 77058, USA

Affiliations  |  Corresponding Author  |  Cite as

Fries, M., Christou, A., Archer, D., Conrad, P., Cooke, W., Eigenbrode, J., ten Kate, I.L., Matney, M., Niles, P., Sykes, M., Steele, A., Treiman, A. (2016) A cometary origin for martian atmospheric methane. Geochem. Persp. Let. 2, 10-23.

Geochemical Perspectives Letters v2, n1  |  doi: 10.7185/geochemlet.1602
Received 15 July 2015  |  Accepted 1 November 2015  |  Published 2 December 2015
Copyright © 2016 European Association of Geochemistry

Keywords: Mars, methane atmosphere, atmospheric chemistry, comet, meteor shower, organic chemistry



top

Abstract


Methane has been reported repeatedly in the martian atmosphere but its origin remains an obstinate mystery. Possible sources include aqueous alteration of igneous rocks, release from ancient deposits of methane/water ice clathrates, infall from exogenous sources such as background interplanetary dust, or biological activity. All of these sources are problematic, however. We hypothesise that delivery of cometary material includes meteor outbursts, commonly known as “meteor showers”, may explain martian methane plumes. Correlations exist between the appearance of methane and near-approaches between Mars and cometary orbits. Additional correlations are seen between these interactions and the appearance of high-altitude dust clouds on Mars, showing that large amounts of material may be deposited on Mars during these encounters. Methane is released by UV breakdown of delivered cometary material. This hypothesis is testable in future Mars/cometary encounters. A cometary origin for methane would reveal formation of methane through processes that are separate from any geological or biological processes on Mars.

Figures and Tables

Table 1 Reported detections on Mars and potential correlations with cometary dust streams.

Figure 1 (left) Image adapted from Sánchez-Lavega et al. (2015) showing a high-altitude dust plume that was seen to appear suddenly on Mars. (right) The locations of Mars and the orbit of comet C/2007 H2 Skiff on 17 May 1997, the same day the dust plume appeared. The motion of Mars is shown by the red arrow and the motion of debris along the orbit of comet Skiff is shown by the blue arrow. Image: JPL Small Bodies Database.

Figure 2 (left) Methane plume reported by Mumma et al. (2009) showing methane detected in the martian atmosphere on 11 Jan 2003. Image originally from NASA. (right) The locations of Mars and the orbit of comet C/2007 H2 Skiff four days before the methane detection, approximately as seen from Earth. The red arrow shows Mars’ direction and the blue arrow shows the movement of debris along Skiff’s orbit. Image: JPL Small Bodies Database.

Table 2 Approximate upcoming Mars / cometary orbit encounters.

Table 1 Figure 1 Figure 2 Table 2

View all figures and tables  


Supplementary Figures and Tables

Figure S-1 Comparison of meteor showers and IDP flux on Earth to appearance of methane on Mars. (left) The Zenith Hourly Rate (ZHR) of meteors over the course of a year (1994) with the background sporadic flux (red line) superimposed by meteor shower activity (labelled meteor showers appear as spikes, e.g., Leo = Leonids) (adapted from Jenniskens, 2006). (right) All methane observations to date for Mars, colour-coded to the papers they derive from and plotted with respect to Mars’ position on its orbital path (LS). Note the general similarity in behaviour between the two graphs – a mildly fluctuating background superimposed by periodic spikes of activity.

Figure S-2 Detections of methane by the Mars Science Laboratory (MSL) rover as a function of LS, or position of Mars on its orbital path. Vertical bars indicate the LS dates for interactions between Mars and the orbits of 5335 Damocles (LS = 47.8) and 1P/Halley (LS = 325.9). Note that detections of methane by MSL occur after these interaction dates (Webster et al., 2015).

Figure S-3 Wong et al. (2003) reports that UV photolysis of methane dominates at high altitudes above 80 km (solid black line labeled “CH4 + hν”). Any previous work that assumed a ground-level origin for martian methane has not considered the strong influence of this reaction when considering methane survival rates. It is possible that a cometary origin for martian methane would preferentially populate higher altitudes, exposing the methane to UV photolysis and accounting for the strong methane destruction rate noted by Webster et al. (2014)(adapted from Wong et al., 2003).

Figure S-1 Figure S-2 Figure S-3

View all supplementary figures and tables  


top

Introduction


Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997

Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.

, 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

; Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

; Krasnopolsky, 2011

Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.

), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004

Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.

), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

). The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997

Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.

), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

; Formisano et al., 2004

Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.

; Krasnopolsky, 2011

Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.

), several non-detections of methane (Villanueva et al., 2013

Villanueva, G.L., Mumma, M.J., Novak, R.E., Radeva, Y.L., Kaüfl, H.U., Smette, A., Tokunaga, A., Khayat, A., Encrenaz, T., Hartogh, P. (2013) A sensitive search for organics (CH4, CH3OH, H2CO, C2H6, C2H2, C2H4), hydroperoxyl (HO2), nitrogen compounds (N2O, NH3, HCN) and chlorine species (HCl, CH3Cl) on Mars using ground-based high-resolution infrared spectroscopy. Icarus 222, 11-27.

; Webster et al., 2014

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Farley, K.A. (2014) Non-detection of methane in the Mars atmosphere by the Curiosity rover. NASA Technical Reports Server, Document 20140010165.

), and “plumes” ranging up to ~45 (Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

; Geminale et al., 2011

Geminale, A., Formisano,V., Sindoni, G. (2011) Mapping methane in martian atmosphere with PFS-MEX data. Planetary and Space Science 59, 137-148.

) to 60 ppbv (Fonti and Marzo, 2010

Fonti, S., Marzo, G.A. (2010) Mapping the methane on Mars. Astronomy & Astrophysics 512, A51.

). Local plumes of methane have been noted over Syrtis Major (Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

), the north polar region (Geminale et al., 2011

Geminale, A., Formisano,V., Sindoni, G. (2011) Mapping methane in martian atmosphere with PFS-MEX data. Planetary and Space Science 59, 137-148.

), Valles Marineris (Krasnopolsky et al., 1997

Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.

) and other localities, but plumes have not been observed to re-occur at the same sites. Similarly, statistical studies of data from Mars-orbiting satellites also show that while methane concentrations vary regionally, those variations are not predictably consistent with latitude, longitude, or seasonal changes on the planet (Geminale et al., 2008

Geminale, A., Formisano,V., Giuranna, M. (2008) Methane in martian atmosphere: spatial, diurnal, and seasonal behavior. Planetary and Space Science 56, 1194-1203.

, 2011

Geminale, A., Formisano,V., Sindoni, G. (2011) Mapping methane in martian atmosphere with PFS-MEX data. Planetary and Space Science 59, 137-148.

; Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

).

To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005

Oze, C., Sharma, M. (2005) Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars. Geophysical Research Letters 32.

), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007

Chastain, B.K., Chevrier, V. (2007) Methane clathrate hydrates as a potential source for martian atmospheric methane. Planetary and Space Science 55, 1246-1256.

), or via biological activity (Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

). Methane that was recently reported in martian meteorites (Blarney et al., 2015

Blarney, N., Parnell, J., McMahon, S., Mark, D., Tomkinson, T., Lee, M., Shivak, J., Izawa, M., Banerjee, N., Flemming, R. (2015) Evidence for methane martian meteorites. Nature Communications 6, 7399.

) may arise from serpentinisation or condensation from a carbon-bearing gas during crystallisation of its parent magma at low oxygen fugacity (Steele et al., 2012

Steele, A., McCubbin, F., Fries, M., Kater, L., Boctor, N., Fogel, M., Conrad, P., Glamoclija, M., Spencer, M., Morrow, A., Hammond, M., Zare, R., Vicenzi, E., Siljestrom, S., Bowden, R., Herd, C., Mysen, B., Shirey, S., Amundsen, H., Treiman, A., Bullock, E., Jull, A. (2012) A reduced organic carbon component in martian basalts. Science 337, 212-215.

). It is not clear at present whether the meteorite-hosted methane reported in Blarney et al. (2015)

Blarney, N., Parnell, J., McMahon, S., Mark, D., Tomkinson, T., Lee, M., Shivak, J., Izawa, M., Banerjee, N., Flemming, R. (2015) Evidence for methane martian meteorites. Nature Communications 6, 7399.

is related to atmospheric methane. Since neither total methane abundance nor mineralogical context are provided by the method used, it is not currently clear whether the methane is a new discovery or a component of the reduced carbon already known to exist at 20 ± 6 ppm concentration in martian meteorites (Steele et al., 2012

Steele, A., McCubbin, F., Fries, M., Kater, L., Boctor, N., Fogel, M., Conrad, P., Glamoclija, M., Spencer, M., Morrow, A., Hammond, M., Zare, R., Vicenzi, E., Siljestrom, S., Bowden, R., Herd, C., Mysen, B., Shirey, S., Amundsen, H., Treiman, A., Bullock, E., Jull, A. (2012) A reduced organic carbon component in martian basalts. Science 337, 212-215.

). Identifying the source(s) of martian methane has potentially far-reaching importance, particularly with biogenesis as one hypothesis. Previous investigations have examined and rejected exogenous material as a source of martian methane, specifically via IDP infall and cometary impacts (Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

; Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

).

There is a third type of exogenous source, however, that may satisfy the observed features of martian methane, namely its sudden appearance, regional scale spatial distribution, and total methane mass observed for past martian plumes. We hypothesise that this potential exogenous source of martian methane, including the appearance of plumes, may be explained by infall of carbonaceous material delivered into the martian atmosphere by periodic, cometary-origin meteor outbursts (or “meteor showers”). This mechanism may also explain the recently reported appearance of high-altitude dust plumes on Mars (Sánchez-Lavega et al., 2015

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke, W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

).

The scope of this study includes statement of a new hypothesis for formation of martian atmospheric methane via meteor outbursts, and a re-analysis of existing methane and high-altitude dust detections on Mars as a test of the hypothesis. The meteor-outburst hypothesis is inherently testable and so a strategy is presented for doing so, using currently available techniques that have been successfully employed in the past, such as Earth-based observations of methane, detection of cometary infall by orbital assets (Jakosky et al., 2015

Jakosky, B., Grebowsky, J., Luhmann, J. (2015) Early MAVEN Results on the Mars Upper Atmosphere and Atmospheric Loss to Space. AAS/AGU Triennial Earth-Sun Summit 1, 20901.

), and methane detection by the Mars Science Laboratory rover (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

).

top

Background


All prior hypotheses for the origin of methane in the martian atmosphere present significant challenges (Lefevre and Forget, 2009

Lefevre, F., Forget, F. (2009) Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics. Nature 460, 720-723.

; Zahnle et al., 2011

Zahnle, K., Freedman, R.S., Catling, D.C. (2011) Is there methane on Mars? Icarus 212, 493-503.

), and thus no consensus has yet emerged on methane origin. While volcanic activity (Wong et al., 2003

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

) could potentially release methane in episodic outbursts, multiple studies have rejected that model because the martian atmosphere lacks SO2 of volcanic origin (Wong et al., 2003

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

; Krasnopolsky, 2011

Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.

), indicating that substantial volcanic activity has not occurred recently. Conversely, both serpentinisation and biological activity can produce methane but neither is conducive to sudden production of massive methane plumes such as one reported (Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

) to involve the sudden release of 19,000 tonnes (19 x 105 kg) of CH4.

Exogenous delivery of methane by infall of IDPs or by large impacts has also been proposed. Delivery of interplanetary dust was recently confirmed by the MAVEN mission team, who detected dust at very high altitudes in the martian atmosphere (Andersson et al., 2015

Andersson, L., Weber, T.D., Malaspina, D., Crary, F., Ergun, R.E., Delory, G.T., Fowler, C.M., Morooka, M.W., McEnulty, T., Eriksson, A.I., Andrews, D.J., Horanyi, M., Collette, A., Yelle, R., Jakosky, B.M. (2015) Dust observations at orbital altitudes surrounding Mars. Science 6, 6261.

). An IDP origin for Mars’ methane has been considered and rejected by previous authors (Formisano et al., 2004

Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.

; Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

; Schuerger et al., 2012

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

; Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

) because the steady flux of IDPs cannot explain episodic and transient methane plumes. Cometary impacts (Kress et al., 2004

Kress, M.E., McKay, C.P. (2004) Formation of methane in comet impacts: implications for Earth, Mars, and Titan. Icarus 168, 475-483.

) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

) and near the MSL rover at the time the rover detected methane (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

).

Cometary debris streams (Fig. S-1) also produce infall of exogenous material into the martian atmosphere. This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al., 1986

Sykes, M.V., Lebofsky, L.A., Hunten, D.M., Low, F. (1986) The discovery of dust trails in the orbits of periodic comets. Science 232, 1115-1117.

; Christou and Beurle, 1999

Christou, A.A., Beurle, K. (2010) Meteoroid streams at Mars: possibilities and implications. Planetary and Space Science 47, 1475-1485.

; Treiman and Treiman, 2000

Treiman, A.H., Treiman, J.S. (2000) Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets. Journal of Geophysical Research: Planets (1991–2012),105, 24571-24581.

; Christou, 2004

Christou, A.A. (2004) Predicting Martian and Venusian meteor shower activity. Earth, Moon, and Planets 95, 425-431.

, 2010

Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.

). While generally associated with short-period comets, a debris trail has also been identified in association with the long-period Halley’s comet (Jenniskens, 1995

Jenniskens, P. (1995) Meteor stream activity. 2: Meteor outbursts. Astronomy and Astrophysics 295, 206-235.

). As a consequence of planetary perturbations, trails subsequently evolve into filaments and elongated streams in a larger “tube” about the comet orbit. When Earth, Mars and other bodies pass through such structures on an annual basis, meteor outbursts, or “meteor showers” may be observed (Christou, 2004

Christou, A.A. (2004) Predicting Martian and Venusian meteor shower activity. Earth, Moon, and Planets 95, 425-431.

; Fig. S-1). On Earth, these streams are well known and are actually targeted for collection of cometary material using high-altitude aircraft. Here we examine the temporal, spatial, and mass distributions of “meteor outburst” infall to Mars, and show that it is a plausible candidate as a source of atmospheric methane.

top

Meteor Showers and Methane Detection


As a first test of the meteor shower hypothesis, we have compared the dates of previous methane detections on Mars with Mars’ currently known cometary debris stream interactions (Sykes and Walker, 1992

Sykes, M.V., Walker, R.G. (1992) Cometary dust trails. I. Survey. Icarus 95, 180-210.

; Treiman and Treiman, 2000

Treiman, A.H., Treiman, J.S. (2000) Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets. Journal of Geophysical Research: Planets (1991–2012),105, 24571-24581.

; Christou, 2010

Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.

). Table 1 shows the dates of methane observations along with the names and dates of correlating cometary orbital interactions. All of the methane observations are taken as single observations with the exception of Mars Express data, which are retrieved from the Planetary Fourier Spectrometer (PFS) instrument via a statistical technique over the course of two months. Figure S-2 illustrates the LS dates of methane detections by the MSL rover versus interactions between Mars and the orbits of 5335 Damocles and 1P Halley, indicating that methane detections occurred shortly after Mars interacted with the orbits of those bodies. Values for orbital interaction minimum distances come from Christou (2010)

Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.

and Treiman and Treiman (2000)

Treiman, A.H., Treiman, J.S. (2000) Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets. Journal of Geophysical Research: Planets (1991–2012),105, 24571-24581.

. Results show that all of the methane observations occur within 16 days of the near-intersection of Mars’ orbit with that of a known cometary meteor stream (Table 1). Some are especially striking, such as the exact correlation between a potentially strong, 70 ± 50 ppbv CH4 observation reported in (Krasnopolsky et al., 1997

Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.

), which occurred on the day of an encounter between Mars and debris from the Marsden group of cometary fragments. Similarly, the strong plume noted by Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

occurred only four days after the nominal closest encounter between Mars and the orbit of comet C/2007 H2 Skiff (SI-3). That comet’s orbit passes only ~150,000 km from Mars, less than half the distance from the Earth to the Moon and similar to the very close ~137,000 km pass distance between Mars and comet C/2013 A1 Siding Spring in October of 2014 (SI-1).

Some methane detections can be correlated with the same comet. One example is Comet 1P/Halley, whose orbit had close approaches to Mars at the times of methane detections in 2004 (Formisano et al., 2004

Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.

), and 2013 (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

). In total, all methane detections on Mars to date could be ascribed to close encounters with only seven cometary debris streams (Table 1, Column 5).

Table 1 Reported detections on Mars and potential correlations with cometary dust streams.

DateMixing ratio (ppbv)Days between cometary encounter and detectionEncountered cometary orbitMars/comet orbit distance (10^-3 AU)
Martian methane: Earth-based telescopic observations
Krasnopolsky et al., 1997

Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.

28-Jun-8870 +/- 500(SDA Meteor Shower) Marsden Group Comets16.139*
Krasnopolsky et al., 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

24-Jan-9910 +/- 36C/1854 L1 Klinkerfues4.778*
"27-Jan-9910 +/- 39C/1854 L1 Klinkerfues4.778*
Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

11-Jan-03max. ~40 +/- 64C/2007 H2 Skiff0.845*
Krasnopolsky, 2011

Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.

10-Feb-06~101513P/Olbers26.580*
Martian methane: ESA Mars Express orbiter observations
Formisano et al., 2004

Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.

Jan-Feb 200410 +/- 531P/Halley66.965*
Methane: Mars science laboratory rover
Webster et al., 2014

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Farley, K.A. (2014) Non-detection of methane in the Mars atmosphere by the Curiosity rover. NASA Technical Reports Server, Document 20140010165.

16-Jun-135.78 +/- 2.27161P/Halley66.965*
"23-Jun-132.13 +/- 2.02


"29-Nov-135.48 +/- 2.19165335 Damocles53.630*
"6-Dec-136.88 +/- 2.11


"6-Jan-146.91 +/- 1.84


"28-Jan-149.34 +/- 2.164275P/Hermann8.600**
"17-Mar-140.47 +/- 0.11


"9-Jul-140.9 +/- 0.16


Visible dust: Earth-based/Hubble telescopic observations
Sánchez-Lavega et al., 2015

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

17-May-97
0C/2007 H2 Skiff0.845*
"12-Mar-12
3275P/Hermann8.600**
Non-detections
Villanueva et al., 2013

Villanueva, G.L., Mumma, M.J., Novak, R.E., Radeva, Y.L., Kaüfl, H.U., Smette, A., Tokunaga, A., Khayat, A., Encrenaz, T., Hartogh, P. (2013) A sensitive search for organics (CH4, CH3OH, H2CO, C2H6, C2H2, C2H4), hydroperoxyl (HO2), nitrogen compounds (N2O, NH3, HCN) and chlorine species (HCl, CH3Cl) on Mars using ground-based high-resolution infrared spectroscopy. Icarus 222, 11-27.

6-Jan-060---

19-Aug-090---

20-Nov-090---

28-Apr-100---
Mumma et al., 2009

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

26-Feb-060---
Webster et al., 2014

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Farley, K.A. (2014) Non-detection of methane in the Mars atmosphere by the Curiosity rover. NASA Technical Reports Server, Document 20140010165.

25-Oct-12-0.51 +/- 2.83---

27-Oct-121.43 +/1 2.47---

27-Nov-120.6 +/- 2.15---
"9-Jul-140.99 +/- 2.08


Krasnopolsky, 2011

Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.

7-Dec-090---

*Christou, 2010 Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.
**Treiman and Treiman, 2000 Treiman, A.H., Treiman, J.S. (2000) Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets. Journal of Geophysical Research: Planets (1991–2012),105, 24571-24581.

Download in Excel

Cometary meteor showers could also be responsible for the two high-altitude dust plumes observed over Mars (Sánchez-Lavega et al., 2015

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

). These two optically visible dust plumes occurred at elevations >200 km above the martian surface, well above martian weather or dust storm phenomena (<60 km altitude). The first dust plume, on 17 May 1997, appeared on the same day as the closest approach between Mars and the orbit of comet C/2007 H2 Skiff, whose orbit passes only about 19 Mars diameters from the planet (Fig. 1). It is worth noting that in 2003, the closest approach between the orbit of C/2007 H2 Skiff and Mars was only four days before the large methane plume noted by Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

, consistent with infall from a massive dust stream shed from Skiff (Fig. 2). The second dust plume (Sánchez-Lavega et al., 2015

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

) was noticed on 12 March 2012, three days after the closest approach between Mars and the orbit of comet 275P/Hermann.


Figure 1 (left) Image adapted from Sánchez-Lavega et al. (2015)

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

showing a high-altitude dust plume that was seen to appear suddenly on Mars. (right) The locations of Mars and the orbit of comet C/2007 H2 Skiff on 17 May 1997, the same day the dust plume appeared. The motion of Mars is shown by the red arrow and the motion of debris along the orbit of comet Skiff is shown by the blue arrow. Image: JPL Small Bodies Database.
Full size image | Download in Powerpoint



Figure 2 (left) Methane plume reported by Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

showing methane detected in the martian atmosphere on 11 Jan 2003. Image originally from NASA. (right) The locations of Mars and the orbit of comet C/2007 H2 Skiff four days before the methane detection, approximately as seen from Earth. The red arrow shows Mars’ direction and the blue arrow shows the movement of debris along Skiff’s orbit. Image: JPL Small Bodies Database.
Full size image | Download in Powerpoint

The areal extent of meteor showers is in agreement with the areal extent observed for martian methane plumes. Meteor showers typically peak over a course of hours, depositing material onto an area that can be sub-hemispherical in extent (Jenniskens, 1995

Jenniskens, P. (1995) Meteor stream activity. 2: Meteor outbursts. Astronomy and Astrophysics 295, 206-235.

), which is in agreement with the size of the Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

plume.

At first glance it may appear straightforward to test this hypothesis via a statistical comparison between methane detection events and the known frequency of interactions between Mars and cometary orbits. Unfortunately this approach is ambiguous because the occurrence of a Mars/comet orbit interaction does not guarantee the infall of a sizable amount of material into Mars’ atmosphere (e.g., Jenniskens, 2006

Jenniskens, P. (2006) Meteor showers and their parent comets. Cambridge University Press.

). The distribution of cometary debris along a comet’s orbit is subject to multiple stochastic processes, including the ejection of material from the parent body and dynamical perturbations of debris. Attempts to correlate orbital interactions with methane detection will result in a large number of false negative results.

top

The Methane Source


Having shown that methane ‘plumes’ on Mars are consistent in space and time with meteor shower infall, it remains to be shown that methane can be generated from that infall, and that the mass of methane generated is consistent with the observed baseline and transient abundances. Methane from meteor outbursts is not delivered directly to Mars, but is generated by UV photolysis of macromolecular carbon (MMC) solids under Mars ambient conditions (Keppler et al., 2012

Keppler, F., Vigano, I., McLeod, A., Ott, U., Früchtl, M., Röckmann, T. (2012) Ultraviolet-radiation-induced methane emissions from meteorites and the martian atmosphere. Nature 486, 93-96.

; Schuerger et al., 2012

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

). The amount of methane that can be generated through a combination of IDP flux and meteor showers is generally consistent with historical methane observations on Mars. The abundance of methane in the martian atmosphere is not simply a global average, as seen in Figure S-1. Instead, periods of non-detection are punctuated by occasional observations that are usually around 10 ppbv with episodic plumes featuring local concentrations of up to ~45 and 60 ppbv as explained above. This is broadly consistent with a steady background IDP flux that is punctuated by periodic meteor showers that vary widely in delivered mass (Fig. S-1). Geminale et al. (2008)

Geminale, A., Formisano,V., Giuranna, M. (2008) Methane in martian atmosphere: spatial, diurnal, and seasonal behavior. Planetary and Space Science 56, 1194-1203.

found that 2.7 x 105 kg of CH4 yr-1 are necessary to sustain 10 ppbv methane on Mars. Previous investigations have noted that IDP flux is sufficient to provide this amount (Geminale et al., 2008

Geminale, A., Formisano,V., Giuranna, M. (2008) Methane in martian atmosphere: spatial, diurnal, and seasonal behavior. Planetary and Space Science 56, 1194-1203.

; Keppler et al., 2012

Keppler, F., Vigano, I., McLeod, A., Ott, U., Früchtl, M., Röckmann, T. (2012) Ultraviolet-radiation-induced methane emissions from meteorites and the martian atmosphere. Nature 486, 93-96.

) via UV photolysis of methane from IDPs under Mars-ambient conditions (Keppler et al., 2012

Keppler, F., Vigano, I., McLeod, A., Ott, U., Früchtl, M., Röckmann, T. (2012) Ultraviolet-radiation-induced methane emissions from meteorites and the martian atmosphere. Nature 486, 93-96.

; Schuerger et al., 2012

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

). However, Schuerger et al. (2012)

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

dispute the 10 ppbv finding and calculates that IDP flux provides a global average of 2.2 ppbv CH4. The MSL rover data thus far show a background methane abundance of ~0.7 ppbv (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

), for which Schuerger’s 2.2 ppbv is excessive if MSL’s measurements are representative of the full thickness of the martian atmosphere. Overall, martian methane is at very low abundances at ground level with both non-detections and higher values noted in measurements made through the full height of the martian atmosphere. Also, IDP flux may account for all or some of the steady-state background but cannot account for methane plumes.

Martian methane plumes may be attributable to periodic meteor showers. The appearance of methane plumes correlates with Mars’ interactions with known cometary orbits as seen in Table 1, but meteor showers must produce enough mass to account for observed methane abundance. To produce a 1.9 x 107 kg CH4 plume like that in Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

requires 7.9 x 108 kg of infalling material, assuming 20 % UV photolysis yield (Schuerger et al., 2012

Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).

) of 12 wt. % carbon (Thomas et al., 1993

Thomas, K.L., Blanford, G.E., Keller, L.P., Klöck, W., McKay, D.S. (1993) Carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles. Geochimica et Cosmochimica Acta 57, 1551-1566.

; Flynn, 1996

Flynn, G.J. (1996) The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth, Moon, and Planets 72, 469-474.

). This amount is equal to ~100x the annual IDP flux in a single event. Cometary debris streams can include billions of kg of material in total (Jenniskens, 2006

Jenniskens, P. (2006) Meteor showers and their parent comets. Cambridge University Press.

) spread out into debris streams and Mars would have to interact with a local concentration to generate a meteor shower with a high local methane concentration. Mitigating factors include the fact that the 1.9 x 107 kg value has been challenged (Zahnle et al., 2011

Zahnle, K., Freedman, R.S., Catling, D.C. (2011) Is there methane on Mars? Icarus 212, 493-503.

) as an artifact of terrestrial 13C-bearing methane and probably indicates an upper limit for the plume, and that the comet implicated in the 19 x 105 kg methane detection, C/2007 H2 Skiff, may simply be capable of meteor showers of this magnitude. Material ejected from long period comets such as C/2007 H2 Skiff are known to generate episodic meteor outbursts at the Earth (Flynn and McKay, 1990

Flynn, G.J., McKay, D.S. (1990) An assessment of the meteoritic contribution to the Martian soil. Journal of Geophysical Research: Solid Earth (1978–2012), 95, 14497-14509.

), and the passage of Skiff’s orbit near Mars in 1997 correlates exactly with the appearance of a dust plume that was dense enough to be visible to amateur astronomers on Earth (Sánchez-Lavega et al., 2015

Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.

). Additionally, while Flynn and McKay (1990)

Flynn, G.J., McKay, D.S. (1990) An assessment of the meteoritic contribution to the Martian soil. Journal of Geophysical Research: Solid Earth (1978–2012), 95, 14497-14509.

found that about 3x more cometary material survives unmelted on Mars than on Earth, that paper disregarded material that melts during infall because that carbon does not “survive” the process. This is a valid assumption on Earth where the atmosphere contains ~21 % oxygen and melting a particle will combust the carbonaceous fraction. On Mars, however, the ~95 % CO2 atmosphere should restrict combustion, driving direct devolatilisation of light species to include methane. The melted mass disregarded in Flynn (1996)

Flynn, G.J. (1996) The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth, Moon, and Planets 72, 469-474.

amounts to 29.1 % of the total IDP carbon delivered to Mars annually, constituting significant additional methane from infall sources. The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996

Flynn, G.J. (1996) The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth, Moon, and Planets 72, 469-474.

), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991

Oberst, J., Nakamura, Y. (1991) A search for clustering among the meteoroid impacts detected by the Apollo lunar seismic network. Icarus 91, 315-325.

; Lyytinen and Jenniskens, 2003

Lyytinen, E., Jenniskens, P. (2003) Meteor outbursts from long-period comet dust trails. Icarus 162, 443-452.

; Suggs et al., 2014

Suggs, R.M., Moser, D.E., Cooke, W.J., Suggs, R.J. (2014) The flux of kilogram-sized meteoroids from lunar impact monitoring. Icarus 238, 23-36.

), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985

Gruen, E., Zook, H.A., Fechtig, H., Giese, R.H. (1985) Collisional balance of the meteoritic complex. Icarus 62, 244-272.

). In fact, larger particles are preferentially concentrated in the vicinity of comet orbits (Asher and Izumi, 1998

Asher, D.J., Izumi, K. (1998) Meteor observations in Japan: new implications for a Taurid meteoroid swarm. Monthly Notices of the Royal Astronomical Society 297, 23-27.

; Dubietis and Arlt, 2007

Dubietis, A., Arlt, R. (2007) Taurid resonant-swarm encounters from two decades of visual observations. Monthly Notices of the Royal Astronomical Society 376, 890-894.

), as observed directly in dust trails (Sykes et al., 1986

Sykes, M.V., Lebofsky, L.A., Hunten, D.M., Low, F. (1986) The discovery of dust trails in the orbits of periodic comets. Science 232, 1115-1117.

). Finally, larger masses tend to generate significant amounts of micrometre-sized “smoke” particles upon infall (Klekociuk et al., 2005

Klekociuk, A.R., Brown, P.G., Pack, D.W., ReVelle, D.O., Edwards, W.N., Spalding, R.E., Tagliaferri, E., Yoo, B.B., Zagari, J. (2005) Meteoritic dust from the atmospheric disintegration of a large meteoroid. Nature 436, 1132-1135.

) that may be particularly conducive to generation of methane via UV photolysis due to their large amount of freshly-exposed surface area. These considerations collectively suggest that the total mass of carbon delivered to the martian atmosphere by meteor streams may exceed prior estimates.

Also, two of the methane plumes reported on Mars (Fonti and Marzo, 2010

Fonti, S., Marzo, G.A. (2010) Mapping the methane on Mars. Astronomy & Astrophysics 512, A51.

; Geminale et al., 2011

Geminale, A., Formisano,V., Sindoni, G. (2011) Mapping methane in martian atmosphere with PFS-MEX data. Planetary and Space Science 59, 137-148.

) were recognised only through statistical treatment of orbital imagery data, and so are of uncertain spatial extent. Only the plume reported by Mumma et al. (2009)

Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.

is resolved well enough in area to permit a credible estimate of its total methane mass, and even this has been challenged (Zahnle et al., 2011

Zahnle, K., Freedman, R.S., Catling, D.C. (2011) Is there methane on Mars? Icarus 212, 493-503.

). It is possible that the other two plumes are strong local concentrations of a significantly lower total mass of methane.

top

The Methane Sink


A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky, 2004

Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.

; Geminale et al., 2008

Geminale, A., Formisano,V., Giuranna, M. (2008) Methane in martian atmosphere: spatial, diurnal, and seasonal behavior. Planetary and Space Science 56, 1194-1203.

; Lefevre and Forget, 2009

Lefevre, F., Forget, F. (2009) Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics. Nature 460, 720-723.

; Zahnle et al., 2011

Zahnle, K., Freedman, R.S., Catling, D.C. (2011) Is there methane on Mars? Icarus 212, 493-503.

; Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

). Webster et al. (2015)

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

noted that some mechanism must be responsible for methane destruction that is “a factor of ≥100” more efficient at destroying methane than surface-level UV photolysis (Fig. S-3). However, with the exception of the MSL rover detection, all detections of methane on Mars have been obtained through the full column of the martian atmosphere and the methane has been assumed to originate from, at or near the surface. Furthermore the MSL report is a point measurement for which the areal and altitudinal extent of the methane is unknown. If, instead, methane is generated at high altitude via cometary debris origin, then the destruction kinetics of martian methane must be revisited. Wong et al. (2003)

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

found that UV photolysis at altitudes greater than 80 km above Mars’ surface can dominate the methane destruction rate, which may explain the observed destruction rate of methane on Mars noted by Webster et al. (2015)

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

. The correlation between observed methane depletion rates and the high-altitude methane loss rate is consistent with a cometary debris origin for Mars’ methane. We also considered dust storms as a methane sink but did not find a correlation with methane non-detection (SI-2).

top

Discussion


If the hypothesis of a cometary meteor outburst source for martian methane is proven true, then a long-standing mystery in Mars science will be resolved. Moreover, a new mechanism will be shown that is entirely atmospheric and cometary in origin, with a source that is entirely uninvolved with either martian geology or potential biology. The hypothesis is innately testable with presently deployed assets including investigations at Mars: MSL’s SAM investigation and the instrument suite on the MAVEN mission. The upcoming ESA Trace Gas Orbiter will also serve a valuable role, and of course Earth-based astronomical observations remain a valuable asset. Together, these assets should undergo an extended investigation of martian atmospheric methane that includes long-term monitoring to identify when plumes occur, how long they persist, their extent and total methane mass, and the vertical distribution of methane through the full height of the martian atmosphere. Methods used specifically to test the hypothesis of a cometary origin include observations of martian meteor showers (Adolfsson et al., 1996

Adolfsson, L.G., Gustafson, B.Å., Murray, C.D. (1996) The Martian atmosphere as a meteoroid detector. Icarus 119, 144-152.

; McAuliffe and Christou, 2006

McAuliffe, J.P., Christou, A.A. (2006) Simulating meteor showers in the Martian atmosphere. In: Proceedings of the International Meteor Conference, Oostmalle, Belgium, 15-18 September 2005. International Meteor Organization, 155–160.

; Domokos et al., 2007

Domokos, A., Bell, J.F., Brown, P., Lemmon, M.T., Suggs, R., Vaubaillon, J., Cooke, W. (2007) Measurement of the meteoroid flux at Mars. Icarus 191, 141-150.

) and corresponding detection of magnesium in the martian atmosphere from meteoritic input (Jakosky et al., 2015

Jakosky, B., Grebowsky, J., Luhmann, J. (2015) Early MAVEN Results on the Mars Upper Atmosphere and Atmospheric Loss to Space. AAS/AGU Triennial Earth-Sun Summit 1, 20901.

) at the time of predicted interactions between Mars and cometary orbits, coupled with both areal and vertical distribution of atmospheric methane and high-altitude dust. Upcoming Mars/cometary interactions are listed for this purpose in Table 2. Although meteor shower-origin methane may account for observations of methane seen to date, we stress that it does not necessarily exclude the possibility of methane contributions from other sources. Our hypothesis is not only testable going forward, but presently offers a very promising set of observed correlations that may provide an explanation for previous methane detections on Mars.

Table 2 Approximate upcoming Mars / cometary orbit encounters.
CometDate
275P/Hermann12-Dec-15
C/2007 H2 Skiff8-Mar-16
(SDA Meteor Shower)12-Sep-16
1P/Halley8-Mar-17
13P Olbers10-May-17
5335 Damocles16-Aug-17
Download in Excel

top

Acknowledgements


The authors extend thanks to Drs. David Draper and Petrus Jenniskens, and Ms. Linda Fries for their helpful commentary and assistance. M. Fries also expresses appreciation to Dr. Betsy Pugel for all the caffeine and integrity.

Editor: Eric H. Oelkers

top

References


Adolfsson, L.G., Gustafson, B.Å., Murray, C.D. (1996) The Martian atmosphere as a meteoroid detector. Icarus 119, 144-152.
Show in context

Methods used specifically to test the hypothesis of a cometary origin include observations of martian meteor showers (Adolfsson et al., 1996; McAuliffe and Christou, 2006; Domokos et al., 2007) and corresponding detection of magnesium in the martian atmosphere from meteoritic input (Jakosky et al., 2015) at the time of predicted interactions between Mars and cometary orbits, coupled with both areal and vertical distribution of atmospheric methane and high-altitude dust.
View in article


Andersson, L., Weber, T.D., Malaspina, D., Crary, F., Ergun, R.E., Delory, G.T., Fowler, C.M., Morooka, M.W., McEnulty, T., Eriksson, A.I., Andrews, D.J., Horanyi, M., Collette, A., Yelle, R., Jakosky, B.M. (2015) Dust observations at orbital altitudes surrounding Mars. Science 6, 6261.
Show in context

Delivery of interplanetary dust was recently confirmed by the MAVEN mission team, who detected dust at very high altitudes in the martian atmosphere (Andersson et al., 2015).
View in article


Asher, D.J., Izumi, K. (1998) Meteor observations in Japan: new implications for a Taurid meteoroid swarm. Monthly Notices of the Royal Astronomical Society 297, 23-27.
Show in context

In fact, larger particles are preferentially concentrated in the vicinity of comet orbits (Asher and Izumi, 1998; Dubietis and Arlt, 2007), as observed directly in dust trails (Sykes et al., 1986).
View in article


Blarney, N., Parnell, J., McMahon, S., Mark, D., Tomkinson, T., Lee, M., Shivak, J., Izawa, M., Banerjee, N., Flemming, R. (2015) Evidence for methane martian meteorites. Nature Communications 6, 7399.
Show in context

Methane that was recently reported in martian meteorites (Blarney et al., 2015) may arise from serpentinisation or condensation from a carbon-bearing gas during crystallisation of its parent magma at low oxygen fugacity (Steele et al., 2012).
View in article
It is not clear at present whether the meteorite-hosted methane reported in Blarney et al. (2015) is related to atmospheric methane.
View in article


Chastain, B.K., Chevrier, V. (2007) Methane clathrate hydrates as a potential source for martian atmospheric methane. Planetary and Space Science 55, 1246-1256.
Show in context

To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007), or via biological activity (Krasnopolsky et al., 2004).
View in article


Christou, A.A. (2004) Predicting Martian and Venusian meteor shower activity. Earth, Moon, and Planets 95, 425-431.
Show in context

This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al, 1986; Christou and Beurle, 1999; Treiman and Treiman, 2000; Christou, 2004, 2010).
View in article
As a consequence of planetary perturbations, trails subsequently evolve into filaments and elongated streams in a larger “tube” about the comet orbit. When Earth, Mars and other bodies pass through such structures on an annual basis, meteor outbursts, or “meteor showers” may be observed (Christou, 2004; Fig. S-1).
View in article


Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.
Show in context

This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al, 1986; Christou and Beurle, 1999; Treiman and Treiman, 2000; Christou, 2004, 2010).
View in article
As a first test of the meteor shower hypothesis, we have compared the dates of previous methane detections on Mars with Mars’ currently known cometary debris stream interactions (Sykes and Walker, 1992; Treiman and Treiman, 2000; Christou, 2010).
View in article
Values for orbital interaction minimum distances come from Christou (2010) and Treiman and Treiman, 2000.
View in article
Table 1
View in article
Christou (2010) lists Klinkerfues as an exceptional case, noting that Vaubaillon and Jenniskens (2007) derived a Halley-type comet orbit to link it to an outburst of the ε Eridanids, a weak September shower at the Earth, assuming that comet C/962 B1 was a previous apparition of the same object.
View in Supplementary Information


Christou, A.A., Beurle, K. (1999) Meteoroid streams at Mars: possibilities and implications. Planetary and Space Science 47, 1475-1485.
Show in context

This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al, 1986; Christou and Beurle, 1999; Treiman and Treiman, 2000; Christou, 2004, 2010).
View in article


Domokos, A., Bell, J.F., Brown, P., Lemmon, M.T., Suggs, R., Vaubaillon, J., Cooke, W. (2007) Measurement of the meteoroid flux at Mars. Icarus 191, 141-150.
Show in context

Methods used specifically to test the hypothesis of a cometary origin include observations of martian meteor showers (Adolfsson et al., 1996; McAuliffe and Christou, 2006; Domokos et al., 2007) and corresponding detection of magnesium in the martian atmosphere from meteoritic input (Jakosky et al., 2015) at the time of predicted interactions between Mars and cometary orbits, coupled with both areal and vertical distribution of atmospheric methane and high-altitude dust.
View in article


Dubietis, A., Arlt, R. (2007) Taurid resonant-swarm encounters from two decades of visual observations. Monthly Notices of the Royal Astronomical Society 376, 890-894.
Show in context

In fact, larger particles are preferentially concentrated in the vicinity of comet orbits (Asher and Izumi, 1998; Dubietis and Arlt, 2007), as observed directly in dust trails (Sykes et al., 1986).
View in article


Farrell, W.M., Delory, G.T., Atreya, S.K. (2006) Martian dust storms as a possible sink of atmospheric methane. Geophysical Research Letters 33.
Show in context

Because martian dust storms have been implicated as a possible mechanism for enhancing the destruction rate of martian methane (Farrell et al., 2006), we also examined the appearance of dust storms versus the dates of non-detection of methane.
View in Supplementary Information


Flynn, G.J. (1996) The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth, Moon, and Planets 72, 469-474.
Show in context

To produce a 1.9 x 107 kg CH4 plume like that in Mumma et al. (2009) requires 7.9 x 108 kg of infalling material, assuming 20 % UV photolysis yield (Schuerger et al., 2012) of 12 wt.% carbon (Thomas et al., 1993; Flynn, 1996).
View in article
The melted mass disregarded in Flynn (1996) amounts to 29.1 % of the total IDP carbon delivered to Mars annually, constituting significant additional methane from infall sources.
View in article
The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991; Lyytinen and Jenniskens, 2003; Suggs et al., 2014), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985).
View in article


Flynn, G.J., McKay, D.S. (1990) An assessment of the meteoritic contribution to the Martian soil. Journal of Geophysical Research: Solid Earth (1978–2012), 95, 14497-14509.
Show in context

Material ejected from long period comets such as C/2007 H2 (Skiff) are known to generate episodic meteor outbursts at the Earth (Flynn and McKay, 1990), and the passage of Skiff’s orbit near Mars in 1997 correlates exactly with the appearance of a dust plume that was dense enough to be visible to amateur astronomers on Earth (Sánchez-Lavega et al., 2015).
View in article
Additionally, while Flynn and McKay (1990) found that about 3x more cometary material survives unmelted on Mars than on Earth, that paper disregarded material that melts during infall because that carbon does not “survive” the process.
View in article


Fonti, S., Marzo, G.A. (2010) Mapping the methane on Mars. Astronomy & Astrophysics 512, A51.
Show in context

The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Also, two of the methane plumes reported on Mars (Fonti and Marzo, 2010; Geminale et al., 2011) were recognised only through statistical treatment of orbital imagery data, and so are of uncertain spatial extent.
View in article


Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. (2004) Detection of methane in the atmosphere of Mars. Science 306, 1758-1761.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
An IDP origin for Mars’ methane has been considered and rejected by previous authors (Formisano et al., 2004; Krasnopolsky et al., 2004; Schuerger et al., 2012; Webster et al., 2015) because the steady flux of IDPs cannot explain episodic and transient methane plumes. Cometary impacts (Kress et al., 2004) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004) and near the MSL rover at the time the rover detected methane (Webster et al., 2015).
View in article
Some methane detections can be correlated with the same comet. One example is Comet 1P/Halley, whose orbit had close approaches to Mars at the times of methane detections in 2004 (Formisano et al., 2004), and 2013 (Webster et al., 2015).
View in article
Table 1
View in article


Geminale, A., Formisano, V., Giuranna, M. (2008) Methane in martian atmosphere: spatial, diurnal, and seasonal behavior. Planetary and Space Science 56, 1194-1203.
Show in context

Similarly, statistical studies of data from Mars-orbiting satellites also show that while methane concentrations vary regionally, those variations are not predictably consistent with latitude, longitude, or seasonal changes on the planet (Geminale et al., 2008, 2011; Webster et al., 2015).
View in article
Geminale et al. (2008) found that 2.7 x 105 kg of CH4 yr-1 are necessary to sustain 10 ppbv methane on Mars.
View in article
Previous investigations have noted that IDP flux is sufficient to provide this amount (Geminale et al., 2008; Keppler et al., 2012) via UV photolysis of methane from IDPs under Mars-ambient conditions (Keppler et al., 2012; Schuerger et al., 2012).
View in article
A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky et al., 2004; Geminale et al., 2008; Lefevre and Forget, 2009; Zahnle et al., 2011;Webster et al., 2015).
View in article


Geminale, A., Formisano, V., Sindoni, G. (2011) Mapping methane in martian atmosphere with PFS-MEX data. Planetary and Space Science 59, 137-148.
Show in context

The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Local plumes of methane have been noted over Syrtis Major (Mumma et al., 2009), the north polar region (Geminale et al., 2011), Valles Marineris (Krasnopolsky et al., 1997) and other localities, but plumes have not been observed to re-occur at the same sites.
View in article
Similarly, statistical studies of data from Mars-orbiting satellites also show that while methane concentrations vary regionally, those variations are not predictably consistent with latitude, longitude, or seasonal changes on the planet (Geminale et al., 2008, 2011; Webster et al., 2015).
View in article
Also, two of the methane plumes reported on Mars (Fonti and Marzo, 2010; Geminale et al., 2011) were recognised only through statistical treatment of orbital imagery data, and so are of uncertain spatial extent.
View in article


Gruen, E., Zook, H.A., Fechtig, H., Giese, R.H. (1985) Collisional balance of the meteoritic complex. Icarus 62, 244-272.
Show in context

The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991; Lyytinen and Jenniskens, 2003; Suggs et al., 2014), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985).
View in article


Jakosky, B., Grebowsky, J., Luhmann, J. (2015) Early MAVEN Results on the Mars Upper Atmosphere and Atmospheric Loss to Space. AAS/AGU Triennial Earth-Sun Summit 1, 20901.
Show in context

The meteor-outburst hypothesis is inherently testable and so a strategy is presented for doing so, using currently available techniques that have been successfully employed in the past, such as Earth-based observations of methane, detection of cometary infall by orbital assets (Jakosky et al., 2015), and methane detection by the Mars Science Laboratory rover (Webster et al., 2015).
View in article
Methods used specifically to test the hypothesis of a cometary origin include observations of martian meteor showers (Adolfsson et al., 1996; McAuliffe and Christou, 2006; Domokos et al., 2007) and corresponding detection of magnesium in the martian atmosphere from meteoritic input (Jakosky et al., 2015) at the time of predicted interactions between Mars and cometary orbits, coupled with both areal and vertical distribution of atmospheric methane and high-altitude dust.
View in article
Nonetheless, the encounter proved the capabilities of robotic probes to observe chemical changes in the upper martian atmosphere due to infalling cometary material (Jakosky et al., 2015) and this will be useful in future encounters.
View in Supplementary Information


Jenniskens, P. (1995) Meteor stream activity. 2: Meteor outbursts. Astronomy and Astrophysics 295, 206-235.
Show in context

While generally associated with short-period comets, a debris trail has also been identified in association with the long-period Halley’s comet (Jenniskens, 1995).
View in article
Meteor showers typically peak over a course of hours, depositing material onto an area that can be sub-hemispherical in extent (Jenniskens, 1995), which is in agreement with the size of the Mumma et al. (2009) plume.
View in article


Jenniskens, P. (2006) Meteor showers and their parent comets. Cambridge University Press.
Show in context

Unfortunately this approach is ambiguous because the occurrence of a Mars/comet orbit interaction does not guarantee the infall of a sizable amount of material into Mars’ atmosphere (e.g., Jenniskens, 2006).
View in article
Cometary debris streams can include billions of kg of material in total (Jenniskens, 2006) spread out into debris streams and Mars would have to interact with a local concentration to generate a meteor shower with a high local methane concentration.
View in article
Figure S-1 (left) [...] The Zenith Hourly Rate (ZHR) of meteors over the course of a year (1994) with the background sporadic flux (red line) superimposed by meteor shower activity (labelled meteor showers appear as spikes, e.g., Leo = Leonids) (adapted from Jenniskens, 2006).
View in Supplementary Information


Kelley, M.S., Farnham, T.L., Bodewits, D., Tricarico, P., Farnocchia, D. (2014) A Study of Dust and Gas at Mars from Comet C/2013 A1 (Siding Spring). The Astrophysical Journal Letters 792, L16.
Show in context

A martian analogue to a meteor outburst occurred in October 2014 with the close interaction between Mars and comet C/2013 A1 Siding Spring (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014).
View in Supplementary Information
The total amount of solid material transferred from Siding Spring to Mars was on the order of only 100 kg (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014) and so any potential methane production was expected to be minor.
View in Supplementary Information


Keppler, F., Vigano, I., McLeod, A., Ott, U., Früchtl, M., Röckmann, T. (2012) Ultraviolet-radiation-induced methane emissions from meteorites and the martian atmosphere. Nature 486, 93-96.
Show in context

Methane from meteor outbursts is not delivered directly to Mars, but is generated by UV photolysis of macromolecular carbon (MMC) solids under Mars ambient conditions (Keppler et al., 2012; Schuerger et al., 2012).
View in article
Previous investigations have noted that IDP flux is sufficient to provide this amount (Geminale et al., 2008; Keppler et al., 2012) via UV photolysis of methane from IDPs under Mars-ambient conditions (Keppler et al., 2012; Schuerger et al., 2012).
View in article


Klekociuk, A.R., Brown, P.G., Pack, D.W., ReVelle, D.O., Edwards, W.N., Spalding, R.E., Tagliaferri, E., Yoo, B.B., Zagari, J. (2005) Meteoritic dust from the atmospheric disintegration of a large meteoroid. Nature 436, 1132-1135.
Show in context

Finally, larger masses tend to generate significant amounts of micrometre-sized “smoke” particles upon infall (Klekociuk et al., 2005) that may be particularly conducive to generation of methane via UV photolysis due to their large amount of freshly-exposed surface area.
View in article


Krasnopolsky, V.A. (2011) Search for methane and upper limits to ethane and SO2 on Mars. Icarus 217, 144-152.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
While volcanic activity (Wong et al., 2003) could potentially release methane in episodic outbursts, multiple studies have rejected that model because the martian atmosphere lacks SO2 of volcanic origin (Wong et al., 2003; Krasnopolsky, 2011), indicating that substantial volcanic activity has not occurred recently.
View in article
Table 1
View in article


Krasnopolsky, V.A., Bjoraker, G.L., Mumma, M.J., Jennings, D.E. (1997) High-resolution spectroscopy of Mars at 3.7 and 8 µm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO. Journal of Geophysical Research 102, 6525-6534.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Local plumes of methane have been noted over Syrtis Major (Mumma et al., 2009), the north polar region (Geminale et al., 2011), Valles Marineris (Krasnopolsky et al., 1997) and other localities, but plumes have not been observed to re-occur at the same sites.
View in article
Some are especially striking, such as the exact correlation between a potentially strong, 70 ± 50 ppbv CH4 observation reported in (Krasnopolsky et al., 1997), which occurred on the day of an encounter between Mars and debris from the Marsden group of cometary fragments.
View in article
Table 1
View in article


Krasnopolsky, V.A., Maillard, J.P., Owen, T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus 172, 537-547.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007), or via biological activity (Krasnopolsky et al., 2004).
View in article
Previous investigations have examined and rejected exogenous material as a source of martian methane, specifically via IDP infall and cometary impacts (Krasnopolsky et al., 2004; Webster et al., 2015).
View in article
An IDP origin for Mars’ methane has been considered and rejected by previous authors (Formisano et al., 2004; Krasnopolsky et al., 2004; Schuerger et al., 2012; Webster et al., 2015) because the steady flux of IDPs cannot explain episodic and transient methane plumes.
View in article
Cometary impacts (Kress et al., 2004) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004) and near the MSL rover at the time the rover detected methane (Webster et al., 2015).
View in article
Table 1
View in article
A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky et al., 2004; Geminale et al., 2008; Lefevre and Forget, 2009; Zahnle et al., 2011;Webster et al., 2015).
View in article


Kress, M.E., McKay, C.P. (2004) Formation of methane in comet impacts: implications for Earth, Mars, and Titan. Icarus 168, 475-483.
Show in context

Cometary impacts (Kress et al., 2004) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004) and near the MSL rover at the time the rover detected methane (Webster et al., 2015).
View in article


Lefevre, F., Forget, F. (2009) Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics. Nature 460, 720-723.
Show in context

All prior hypotheses for the origin of methane in the martian atmosphere present significant challenges (Lefevre and Forget, 2009; Zahnle et al., 2011), and thus no consensus has yet emerged on methane origin.
View in article
A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky et al., 2004; Geminale et al., 2008; Lefevre and Forget, 2009; Zahnle et al., 2011;Webster et al., 2015).
View in article


Lisano, M.E., Bernard, D. (2014) An Almanac of Martian Dust Storms for In Sight project energy system design. In Aerospace Conference, 1-15.
Show in context

There is no clear correlation between the dates in Table 1 under “Non-Detections” and the dates of martian dust storms presented in the InSight Dust Storm Almanac (Lisano and Bernard, 2014).
View in Supplementary Information


Lyytinen, E., Jenniskens, P. (2003) Meteor outbursts from long-period comet dust trails. Icarus 162, 443-452.
Show in context

The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991; Lyytinen and Jenniskens, 2003; Suggs et al., 2014), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985).
View in article


McAuliffe, J.P., Christou, A.A. (2006) Simulating meteor showers in the Martian atmosphere. In: Proceedings of the International Meteor Conference, Oostmalle, Belgium, 15-18 September 2005. International Meteor Organization, 155–160.
Show in context

Methods used specifically to test the hypothesis of a cometary origin include observations of martian meteor showers (Adolfsson et al., 1996; McAuliffe and Christou, 2006; Domokos et al., 2007) and corresponding detection of magnesium in the martian atmosphere from meteoritic input (Jakosky et al., 2015) at the time of predicted interactions between Mars and cometary orbits, coupled with both areal and vertical distribution of atmospheric methane and high-altitude dust.
View in article


Moores, J.E., McConnochie, T.H., Ming, D.W., Archer, P.D., Schuerger, A.C. (2014) The Siding Spring cometary encounter with Mars: A natural experiment for the Martian atmosphere? Geophysical Research Letters 41, 4109-4117.
Show in context

A martian analogue to a meteor outburst occurred in October 2014 with the close interaction between Mars and comet C/2013 A1 Siding Spring (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014).
View in Supplementary Information
The total amount of solid material transferred from Siding Spring to Mars was on the order of only 100 kg (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014) and so any potential methane production was expected to be minor.
View in Supplementary Information


Moorhead, A.V., Wiegert, P.A., Cooke, W.J. (2014) "The meteoroid fluence at Mars due to comet C/2013 A1 (Siding Spring)." Icarus 231, 13-21.
Show in context

A martian analogue to a meteor outburst occurred in October 2014 with the close interaction between Mars and comet C/2013 A1 Siding Spring (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014).
View in Supplementary Information
The total amount of solid material transferred from Siding Spring to Mars was on the order of only 100 kg (Kelley et al., 2014; Moores et al., 2014; Moorhead et al., 2014) and so any potential methane production was expected to be minor.
View in Supplementary Information


Mumma, M.J., Villanueva, G.L., Novak, R.E., Hewagama, T., Bonev, B.P., DiSanti, M.A., Mandell, A.M., Smith, M.D. (2009) Strong release of methane on Mars in northern summer 2003. Science 323, 1041-1045.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Local plumes of methane have been noted over Syrtis Major (Mumma et al., 2009), the north polar region (Geminale et al., 2011), Valles Marineris (Krasnopolsky et al., 1997) and other localities, but plumes have not been observed to re-occur at the same sites.
View in article
Conversely, both serpentinisation and biological activity can produce methane but neither is conducive to sudden production of massive methane plumes such as one reported (Mumma et al., 2009) to involve the sudden release of 19,000 tonnes (19 x 105 kg) of CH4.
View in article
Similarly, the strong plume noted by Mumma et al. (2009) occurred only four days after the nominal closest encounter between Mars and the orbit of comet C/2007 H2 Skiff.
View in article
Table 1
View in article
It is worth noting that in 2003, the closest approach between the orbit of C/2007 H2 Skiff and Mars was only four days before the large methane plume noted by Mumma et al. (2009), consistent with infall from a massive dust stream shed from Skiff (Fig. 2).
View in article
Figure 2 (left) Methane plume reported by Mumma et al. (2009) showing methane detected in the martian atmosphere on 11 Jan 2003.
View in article
Meteor showers typically peak over a course of hours, depositing material onto an area that can be sub-hemispherical in extent (Jenniskens, 1995), which is in agreement with the size of the Mumma et al. (2009) plume.
View in article
To produce a 1.9 x 107 kg CH4 plume like that in Mumma et al. (2009) requires 7.9 x 108 kg of infalling material, assuming 20 % UV photolysis yield (Schuerger et al., 2012) of 12 wt.% carbon (Thomas et al., 1993; Flynn, 1996).
View in article
Only the plume reported by Mumma et al. (2009) is resolved well enough in area to permit a credible estimate of its total methane mass, and even this has been challenged (Zahnle et al., 2011).
View in article


Oberst, J., Nakamura, Y. (1991) A search for clustering among the meteoroid impacts detected by the Apollo lunar seismic network. Icarus 91, 315-325.
Show in context

The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991; Lyytinen and Jenniskens, 2003; Suggs et al., 2014), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985).
View in article


Oze, C., Sharma, M. (2005) Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars. Geophysical Research Letters 32.
Show in context

To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007), or via biological activity (Krasnopolsky et al., 2004).
View in article


Sánchez-Lavega, A., García Muñoz, A., García-Melendo, E., Pérez-Hoyos, S., Gómez-Forrellad, J.M., Pellier, C., Delcroix, M., López-Valverde, M. A., González-Galindo, F., Jaeschke,W., Parker, D., Phillips, J., Peach, D. (2015) An extremely high-altitude plume seen at Mars’ morning terminator. Nature 518, 525-528.
Show in context

This mechanism may also explain the recently reported appearance of high-altitude dust plumes on Mars (Sánchez-Lavega et al., 2015).
View in article
Table 1
View in article
Cometary meteor showers could also be responsible for the two high-altitude dust plumes observed over Mars (Sánchez-Lavega et al., 2015).
View in article
The second dust plume (Sánchez-Lavega et al., 2015) was noticed on 12 March 2012, three days after the closest approach between Mars and the orbit of comet 275P/Hermann.
View in article
Figure 1 (left) Image adapted from Sánchez-Lavega et al. (2015) showing a high-altitude dust plume that was seen to appear suddenly on Mars.
View in article
Material ejected from long period comets such as C/2007 H2 (Skiff) are known to generate episodic meteor outbursts at the Earth (Flynn and McKay, 1990), and the passage of Skiff’s orbit near Mars in 1997 correlates exactly with the appearance of a dust plume that was dense enough to be visible to amateur astronomers on Earth (Sánchez-Lavega et al., 2015).
View in article


Schuerger, A.C., Moores, J.E., Clausen, C.A., Barlow, N.G., Britt, D.T. (2012) Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions. Journal of Geophysical Research: Planets (1991–2012), 117(E8).
Show in context

To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007), or via biological activity (Krasnopolsky et al., 2004).
View in article
An IDP origin for Mars’ methane has been considered and rejected by previous authors (Formisano et al., 2004; Krasnopolsky et al., 2004; Schuerger et al., 2012; Webster et al., 2015) because the steady flux of IDPs cannot explain episodic and transient methane plumes. Cometary impacts (Kress et al., 2004) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004) and near the MSL rover at the time the rover detected methane (Webster et al., 2015).
View in article
Methane from meteor outbursts is not delivered directly to Mars, but is generated by UV photolysis of macromolecular carbon (MMC) solids under Mars ambient conditions (Keppler et al., 2012; Schuerger et al., 2012).
View in article
Previous investigations have noted that IDP flux is sufficient to provide this amount (Geminale et al., 2008; Keppler et al., 2012) via UV photolysis of methane from IDPs under Mars-ambient conditions (Keppler et al., 2012; Schuerger et al., 2012).
View in article
However, Schuerger et al. (2012) disputes the 10 ppbv finding and calculates that IDP flux provides a global average of 2.2 ppbv CH4.
View in article
To produce a 1.9 x 107 kg CH4 plume like that in Mumma et al. (2009) requires 7.9 x 108 kg of infalling material, assuming 20 % UV photolysis yield (Schuerger et al., 2012) of 12 wt.% carbon (Thomas et al., 1993; Flynn, 1996).
View in article


Steele, A., McCubbin, F., Fries, M., Kater, L., Boctor, N., Fogel, M., Conrad, P., Glamoclija, M., Spencer, M., Morrow, A., Hammond, M., Zare, R., Vicenzi, E., Siljestrom, S., Bowden, R., Herd, C., Mysen, B., Shirey, S., Amundsen, H., Treiman, A., Bullock, E., Jull, A. (2012) A reduced organic carbon component in martian basalts. Science 337, 212-215.
Show in context

Methane that was recently reported in martian meteorites (Blarney et al., 2015) may arise from serpentinisation or condensation from a carbon-bearing gas during crystallisation of its parent magma at low oxygen fugacity (Steele et al., 2012).
View in article
Since neither total methane abundance nor mineralogical context are provided by the method used, it is not currently clear whether the methane is a new discovery or a component of the reduced carbon already known to exist at 20 ± 6 ppm concentration in martian meteorites (Steele et al., 2012).
View in article


Suggs, R.M., Moser, D.E., Cooke, W.J., Suggs, R.J. (2014) The flux of kilogram-sized meteoroids from lunar impact monitoring. Icarus 238, 23-36.
Show in context

The portion of particles experiencing greater than 50 % melting is composed of particles greater than 10-4 g in mass (Flynn, 1996), and this larger mass fraction is important because lunar impact monitoring programs indicate that meteor streams contain a higher flux of large (>30 g) meteoroids than the IDP population (Oberst and Nakamura, 1991; Lyytinen and Jenniskens, 2003; Suggs et al., 2014), which is dominated by particles of 10-6-10-4 g (Gruen et al., 1985).
View in article


Sykes, M.V., Walker, R.G. (1992) Cometary dust trails. I. Survey. Icarus 95, 180-210.
Show in context

As a first test of the meteor shower hypothesis, we have compared the dates of previous methane detections on Mars with Mars’ currently known cometary debris stream interactions (Sykes and Walker, 1992; Treiman and Treiman, 2000; Christou, 2010).
View in article


Sykes, M.V., Lebofsky, L.A., Hunten, D.M., Low, F. (1986) The discovery of dust trails in the orbits of periodic comets. Science 232, 1115-1117.
Show in context

This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al, 1986; Christou and Beurle, 1999; Treiman and Treiman, 2000; Christou, 2004, 2010).
View in article
In fact, larger particles are preferentially concentrated in the vicinity of comet orbits (Asher and Izumi, 1998; Dubietis and Arlt, 2007), as observed directly in dust trails (Sykes et al., 1986).
View in article


Thomas, K.L., Blanford, G.E., Keller, L.P., Klöck, W., McKay, D.S. (1993) Carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles. Geochimica et Cosmochimica Acta 57, 1551-1566.
Show in context

To produce a 1.9 x 107 kg CH4 plume like that in Mumma et al. (2009) requires 7.9 x 108 kg of infalling material, assuming 20 % UV photolysis yield (Schuerger et al., 2012) of 12 wt.% carbon (Thomas et al., 1993; Flynn, 1996).
View in article


Treiman, A.H., Treiman, J.S. (2000) Cometary dust streams at Mars: Preliminary predictions from meteor streams at Earth and from periodic comets. Journal of Geophysical Research: Planets (1991–2012),105, 24571-24581.
Show in context

This material arises from low-velocity emissions of large particles, forming trails spanning portions of a comet’s orbit (Sykes et al, 1986; Christou and Beurle, 1999; Treiman and Treiman, 2000; Christou, 2004, 2010).
View in article
As a first test of the meteor shower hypothesis, we have compared the dates of previous methane detections on Mars with Mars’ currently known cometary debris stream interactions (Sykes and Walker, 1992; Treiman and Treiman, 2000; Christou, 2010).
View in article
Values for orbital interaction minimum distances come from Christou (2010) and Treiman and Treiman, 2000.
View in article
Table 1
View in article


Vaubaillon, J., Jenniskens, P. (2007) Dust trail evolution applied to long-period comet C/1854 L1 (Klinkerfues) and the ε-Eridanids. Advances in Space Research 39, 612-615.
Show in context

Christou (2010) lists Klinkerfues as an exceptional case, noting that Vaubaillon and Jenniskens (2007) derived a Halley-type comet orbit to link it to an outburst of the ε Eridanids, a weak September shower at the Earth, assuming that comet C/962 B1 was a previous apparition of the same object.
View in Supplementary Information


Villanueva, G.L., Mumma, M.J., Novak, R.E., Radeva, Y.L., Kaüfl, H.U., Smette, A., Tokunaga, A., Khayat, A., Encrenaz, T., Hartogh, P. (2013) A sensitive search for organics (CH4, CH3OH, H2CO, C2H6, C2H2, C2H4), hydroperoxyl (HO2), nitrogen compounds (N2O, NH3, HCN) and chlorine species (HCl, CH3Cl) on Mars using ground-based high-resolution infrared spectroscopy. Icarus 222, 11-27.
Show in context

The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Table 1
View in article


Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Farley, K.A. (2014) Non-detection of methane in the Mars atmosphere by the Curiosity rover. NASA Technical Reports Server, Document 20140010165.
Show in context

The earliest report of methane to withstand scrutiny was made in June of 1988 (Krasnopolsky et al., 1997), and reports made since that date include several values of ~10 parts per billion by volume (ppbv) over large spatial scales (Krasnopolsky et al., 2004; Formisano et al., 2004; Krasnopolsky, 2011), several non-detections of methane (Villanueva et al., 2013; Webster et al., 2014), and “plumes” ranging up to ~45 (Mumma et al., 2009; Geminale et al., 2011) to 60 ppbv (Fonti and Marzo, 2010).
View in article
Table 1
View in article
Figure S-3 [...] It is possible that a cometary origin for martian methane would preferentially populate higher altitudes, exposing the methane to UV photolysis and accounting for the strong methane destruction rate noted by Webster et al. (2014) (adapted from Wong et al., 2003).
View in Supplementary Information


Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.
Show in context

Investigators have reported methane in the martian atmosphere using a variety of analytical techniques, including Earth-based astronomical observations (Krasnopolsky et al., 1997, 2004; Mumma et al., 2009; Krasnopolsky, 2011), the Planetary Fourier Spectrometer on the ESA Mars Express mission (Formisano et al., 2004), and recently by the NASA’s Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) mission (Webster et al., 2015).
View in article
Similarly, statistical studies of data from Mars-orbiting satellites also show that while methane concentrations vary regionally, those variations are not predictably consistent with latitude, longitude, or seasonal changes on the planet (Geminale et al., 2008, 2011; Webster et al., 2015).
View in article
Previous investigations have examined and rejected exogenous material as a source of martian methane, specifically via IDP infall and cometary impacts (Krasnopolsky et al., 2004; Webster et al., 2015).
View in article
The meteor-outburst hypothesis is inherently testable and so a strategy is presented for doing so, using currently available techniques that have been successfully employed in the past, such as Earth-based observations of methane, detection of cometary infall by orbital assets (Jakosky et al., 2015), and methane detection by the Mars Science Laboratory rover (Webster et al., 2015).
View in article
An IDP origin for Mars’ methane has been considered and rejected by previous authors (Formisano et al., 2004; Krasnopolsky et al., 2004; Schuerger et al., 2012; Webster et al., 2015) because the steady flux of IDPs cannot explain episodic and transient methane plumes.
View in article
Cometary impacts (Kress et al., 2004) have also been ruled out due to the lack of young impact craters of suitable size, both on the planetary scale (Krasnopolsky et al., 2004) and near the MSL rover at the time the rover detected methane (Webster et al., 2015).
View in article
One example is Comet 1P/Halley, whose orbit had close approaches to Mars at the times of methane detections in 2004 (Formisano et al., 2004), and 2013 (Webster et al., 2015).
View in article
The MSL rover data thus far show a background methane abundance of ~0.7 ppbv (Webster et al., 2015), for which Schuerger’s 2.2 ppbv is excessive if MSL’s measurements are representative of the full thickness of the martian atmosphere.
View in article
A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky et al., 2004; Geminale et al., 2008; Lefevre and Forget, 2009; Zahnle et al., 2011;Webster et al., 2015).
View in article
Webster et al. (2015) noted that some mechanism must be responsible for methane destruction that is “a factor of ≥100” more efficient at destroying methane than surface-level UV photolysis (Fig. S-3).
View in article
Wong et al. (2003) found that UV photolysis at altitudes greater than 80 km above Mars’ surface can dominate the methane destruction rate, which may explain the observed destruction rate of methane on Mars noted by Webster et al. (2015).
View in article
Figure S-2 [...] Note that detections of methane by MSL occur after these interaction dates (Webster et al., 2015).
View in Supplementary Information


Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.
Show in context

To date, several possible sources for martian methane have been proposed, including: abiological sources such as volcanism (Wong et al., 2003), exogenous sources to include infall of interplanetary dust particles (IDP) and cometary impact material (Schuerger et al., 2012), aqueous alteration of olivine in the presence of carbonaceous material (Oze and Sharma, 2005), release from ancient deposits of methane clathrates (Chastain and Chevrier, 2007), or via biological activity (Krasnopolsky et al., 2004).
View in article
While volcanic activity (Wong et al., 2003) could potentially release methane in episodic outbursts, multiple studies have rejected that model because the martian atmosphere lacks SO2 of volcanic origin (Wong et al., 2003; Krasnopolsky, 2011), indicating that substantial volcanic activity has not occurred recently.
View in article
Wong et al. (2003) found that UV photolysis at altitudes greater than 80 km above Mars’ surface can dominate the methane destruction rate, which may explain the observed destruction rate of methane on Mars noted by Webster et al. (2015).
View in article
Figure S-3 Wong et al. (2003) reports that UV photolysis of methane dominates at high altitudes above 80 km (solid black line labeled “CH4 + hν”). [...] It is possible that a cometary origin for martian methane would preferentially populate higher altitudes, exposing the methane to UV photolysis and accounting for the strong methane destruction rate noted by Webster et al. (2014) (adapted from Wong et al., 2003).
View in Supplementary Information


Zahnle, K., Freedman, R.S., Catling, D.C. (2011) Is there methane on Mars? Icarus 212, 493-503.
Show in context

All prior hypotheses for the origin of methane in the martian atmosphere present significant challenges (Lefevre and Forget, 2009; Zahnle et al., 2011), and thus no consensus has yet emerged on methane origin.
View in article
Mitigating factors include the fact that the 1.9 x 107 kg value has been challenged (Zahnle et al., 2011) as an artifact of terrestrial 13C-bearing methane and probably indicates an upper limit for the plume, and that the comet implicated in the 19 x 105 kg methane detection, C/2007 H2 Skiff, may simply be capable of meteor showers of this magnitude.
View in article
Only the plume reported by Mumma et al. (2009) is resolved well enough in area to permit a credible estimate of its total methane mass, and even this has been challenged (Zahnle et al., 2011).
View in article
A cometary debris origin for martian methane may also assist in explaining the observed methane loss rate, which other authors have noted to be inconsistent with currently understood martian atmospheric and surface chemistry (Krasnopolsky et al., 2004; Geminale et al., 2008; Lefevre and Forget, 2009; Zahnle et al., 2011;Webster et al., 2015).
View in article


top

Supplementary Information


SI-1
A martian analogue to a meteor outburst occurred in October 2014 with the close interaction between Mars and comet C/2013 A1 Siding Spring (Kelley et al., 2014

Kelley, M.S., Farnham, T.L., Bodewits, D., Tricarico, P., Farnocchia, D. (2014) A Study of Dust and Gas at Mars from Comet C/2013 A1 (Siding Spring). The Astrophysical Journal Letters 792, L16.

; Moores et al., 2014

Moores, J.E., McConnochie, T.H., Ming, D.W., Archer, P.D., Schuerger, A.C. (2014) The Siding Spring cometary encounter with Mars: A natural experiment for the Martian atmosphere? Geophysical Research Letters 41, 4109-4117.

; Moorhead et al., 2014

Moorhead, A.V., Wiegert, P.A., Cooke, W.J. (2014) "The meteoroid fluence at Mars due to comet C/2013 A1 (Siding Spring)." Icarus 231, 13-21.

). Siding Spring was observed on a hyperbolic orbit, entering the inner solar system possibly for the first time. Therefore, it had no evolved complex of dust streams and filaments associated with its orbit (associated with periodic comets) and the loading of dust into the Martian atmosphere depended upon the details of dust production beyond the orbit of Saturn and where Mars crossed its orbital plane. The total amount of solid material transferred from Siding Spring to Mars was on the order of only 100 kg (Kelley et al., 2014

Kelley, M.S., Farnham, T.L., Bodewits, D., Tricarico, P., Farnocchia, D. (2014) A Study of Dust and Gas at Mars from Comet C/2013 A1 (Siding Spring). The Astrophysical Journal Letters 792, L16.

; Moores et al., 2014

Moores, J.E., McConnochie, T.H., Ming, D.W., Archer, P.D., Schuerger, A.C. (2014) The Siding Spring cometary encounter with Mars: A natural experiment for the Martian atmosphere? Geophysical Research Letters 41, 4109-4117.

; Moorhead et al., 2014

Moorhead, A.V., Wiegert, P.A., Cooke, W.J. (2014) "The meteoroid fluence at Mars due to comet C/2013 A1 (Siding Spring)." Icarus 231, 13-21.

) and so any potential methane production was expected to be minor. Nonetheless, the encounter proved the capabilities of robotic probes to observe chemical changes in the upper martian atmosphere due to infalling cometary material (Jakosky et al., 2015

Jakosky, B., Grebowsky, J., Luhmann, J. (2015) Early MAVEN Results on the Mars Upper Atmosphere and Atmospheric Loss to Space. AAS/AGU Triennial Earth-Sun Summit 1, 20901.

) and this will be useful in future encounters.

SI-2
Because martian dust storms have been implicated as a possible mechanism for enhancing the destruction rate of martian methane (Farrell et al., 2006

Farrell, W.M., Delory, G.T., Atreya, S.K. (2006) Martian dust storms as a possible sink of atmospheric methane. Geophysical Research Letters 33.

), we also examined the appearance of dust storms versus the dates of non-detection of methane. There is no clear correlation between the dates in Table 1 under “Non-Detections” and the dates of martian dust storms presented in the InSight Dust Storm Almanac (Lisano and Bernard, 2014

Lisano, M.E., Bernard, D. (2014) An Almanac of Martian Dust Storms for In Sight project energy system design. In Aerospace Conference, 1-15.

). Dust storms reported near the dates of non-detection include a global storm in the winter of 2007 and a regional storm in early 2009. All non-detections of methane occur either before these two storms or with cometary interactions between the end of a storm and the date of non-detection. On this basis, dust storms do not appear to contribute to the non-detections available in current literature.

SI-3
For the hypothesis to be valid, the comets with orbital interactions with Mars must be periodic, or “P” type comets. This is because repeated orbits around the Sun are required for a comet to accumulate a debris stream around portions of its orbit and thereby generate meteor showers. Even though comet C/2007 H2 Skiff has been given the “C” designation of a comet on a hyperbolic trajectory, it has been observed as periodic with an orbital period of 352 years (JPL Small Bodies Database) indicating that it is misclassified. Comet C/1854 L1 Klinkerfues also appears on the cometary interactions with Mars listed here despite its “C” designation. Christou (2010)

Christou, A.A. (2010) Annual meteor showers at Venus and Mars: lessons from the Earth. Monthly Notices of the Royal Astronomical Society 402, 2759-2770.

lists Klinkerfues as an exceptional case, noting that Vaubaillon and Jenniskens (2007)

Vaubaillon, J., Jenniskens, P. (2007). Dust trail evolution applied to long-period comet C/1854 L1 (Klinkerfues) and the ε-Eridanids. Advances in Space Research 39, 612-615.

derived a Halley-type comet orbit to link it to an outburst of the ε Eridanids, a weak September shower at the Earth, assuming that comet C/962 B1 was a previous apparition of the same object. Even though they are currently classified as “C” type comets, comets Skiff and Klinkerfues are credible sources if their proposed Halley-type orbits are correct.


Figure S-1 Comparison of meteor showers and IDP flux on Earth to appearance of methane on Mars. (left) The Zenith Hourly Rate (ZHR) of meteors over the course of a year (1994) with the background sporadic flux (red line) superimposed by meteor shower activity (labelled meteor showers appear as spikes, e.g., Leo = Leonids) (adapted from Jenniskens, 2006

Jenniskens, P. (2006) Meteor showers and their parent comets. Cambridge University Press.

). (right) All methane observations to date for Mars, colour-coded to the papers they derive from and plotted with respect to Mars’ position on its orbital path (LS). Note the general similarity in behaviour between the two graphs – a mildly fluctuating background superimposed by periodic spikes of activity.
Full size image | Download in Powerpoint


Figure S-2 Detections of methane by the Mars Science Laboratory (MSL) rover as a function of LS, or position of Mars on its orbital path. Vertical bars indicate the LS dates for interactions between Mars and the orbits of 5335 Damocles (LS = 47.8) and 1P/Halley (LS = 325.9). Note that detections of methane by MSL occur after these interaction dates (Webster et al., 2015

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Mischna, M.A., Meslin, P.-Y., Farley, K.A., Conrad, P.G., Christensen, L.E., Pavlov, A.A., Martin-Torres, J., Zorzano, M.-P., McConnochie, T.H., Owen, T., Eigenbrode, J.L., Glavin, D.P., Steele, A., Malespin, C.A., Archer Jr., P.D., Sutter, B., Coll, P., Frissinet, C., McKay, C.P., Moores, J.E., Schwenzer, S.P., Bridges, J.C., Navarro-Gonzalez, R., Gellert, R., Lemmon, M.T., the MSL Science Team (2015) Mars methane detection and variability at Gale crater. Science 347, 415-417.

).
Full size image | Download in Powerpoint


Figure S-3 Wong et al. (2003)

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

reports that UV photolysis of methane dominates at high altitudes above 80 km (solid black line labeled “CH4 + hν”). Any previous work that assumed a ground-level origin for martian methane has not considered the strong influence of this reaction when considering methane survival rates. It is possible that a cometary origin for martian methane would preferentially populate higher altitudes, exposing the methane to UV photolysis and accounting for the strong methane destruction rate noted by Webster et al. (2014)

Webster, C.R., Mahaffy, P.R., Atreya, S.K., Flesch, G.J., Farley, K.A. (2014) Non-detection of methane in the Mars atmosphere by the Curiosity rover. NASA Technical Reports Server, Document 20140010165.

(adapted from Wong et al., 2003

Wong, A.S., Atreya, S.K., Encrenaz, T. (2003) Chemical markers of possible hot spots on Mars. Journal of Geophysical Research: Planets (1991–2012), 108.

).
Full size image | Download in Powerpoint

top