Methane on Mars


The source of Mars methane is unknown; its detection is shown here.

The reported presence of methane in the atmosphere of Mars is of interest to many geologists and astrobiologists,[1] as methane may indicate the presence of microbial life on Mars, or a geochemical process such as volcanism or hydrothermal activity.[2][3][4][5][6][7]

Since 2004, trace amounts of methane (range from 60 ppbv to under detection limit (< 0.05 ppbv)) have been reported in various missions and observational studies.[8][9][10][11][12] The source of methane on Mars and the explanation for the enormous discrepancy in the observed methane concentrations are still unknown and are under study.[1][13] Whenever methane is detected, it is rapidly removed from the atmosphere by an efficient, yet unknown process.[14]

History of detections

Model of a methane (CH4) molecule

Methane (CH4) is chemically unstable in the current oxidizing atmosphere of Mars. It would quickly break down due to ultraviolet (UV) radiation from the Sun and chemical reactions with other gases. Therefore, a persistent or episodic presence of methane in the atmosphere may imply the existence of a source to continually replenish the gas.

The first evidence of methane in the atmosphere was measured by ESA's Mars Express orbiter with an instrument called the Planetary Fourier Spectrometer.[15] In March 2004, the Mars Express science team suggested the presence of methane in the atmosphere at a concentration of about 10 ppbv.[16][17][18][19] This was confirmed soon after by three ground-based telescope teams, although large differences in the abundances were measured between observations taken in 2003 and 2006. This spatial and temporal variability of the gas suggests that the methane was locally concentrated and probably seasonal.[20] It is estimated that Mars produces 270 tons of methane per year.[21][22]

In 2011, NASA scientists reported a comprehensive search using high-resolution infrared spectroscopy from high-altitude Earth ground-based observatories (VLT, Keck-2, NASA-IRTF) for trace species (including methane) on Mars, deriving sensitive upper limits for methane (< 7 ppbv), ethane (< 0.2 ppbv), methanol (< 19 ppbv) and others (H2CO, C2H2, C2H4, N2O, NH3, HCN, CH3Cl, HCl, HO2 – all with limits at ppbv levels).[23]

Curiosity rover detected a cyclical seasonal variation in atmospheric methane.

In August 2012, the Curiosity rover landed on Mars. The rover's instruments are capable of making precise abundance measurements, but cannot be used to distinguish between different isotopologues of methane and so it cannot determine if it is geophysical or biological in origin.[24] However, the Trace Gas Orbiter (TGO) can measure these ratios and point to their origin.[15]

The first measurements with Curiosity's Tunable Laser Spectrometer (TLS) in 2012 indicated that there was no methane —or less than 5 ppb— at the landing site,[25][26][27] later calculated to a baseline of 0.3 to 0.7 ppbv.[28] In 2013, NASA scientists again reported no detection of methane beyond a baseline.[29][30][31] But in 2014, NASA reported that the Curiosity rover detected a tenfold increase ('spike') in methane in the atmosphere around it in late 2013 and early 2014.[10] Four measurements taken over two months in this period averaged 7.2 ppbv, implying that Mars is episodically producing or releasing methane from an unknown source.[10] Before and after, readings averaged around one-tenth that level.[32][33][10] On 7 June 2018, NASA announced the confirmation of a cyclical seasonal variation in the background level of atmospheric methane.[34][35][36] The largest concentration of methane detected in situ by the Curiosity rover showed a spike to 21 ppbv, during an event in late June 2019.[37][38] The Mars Express orbiter happened to be performing spot tracking in that area 20 hours before Curiosity's methane detection, as well as 24 and 48 hours after the detection,[15] and the TGO was performing atmospheric observations at around the same time but at a higher latitude.[15]

The Indian Mars Orbiter Mission, which entered orbit around Mars on 24 September 2014, is equipped with a Fabry–Pérot interferometer to measure atmospheric methane, but after entering Mars orbit it was determined that it was not capable of detecting methane,[39][40]: 57  so the instrument was repurposed as an albedo mapper.[39][41] As of April 2019, the TGO showed that the concentration of methane is under the detectable level (< 0.05 ppbv).[12][19]

The Perseverance rover (landed Feb 2021) and the Rosalind Franklin rover (due 2023) will not be equipped to analyze the atmospheric methane nor its isotopes,[42][43] so the proposed Mars sample-return mission in the mid-2030s seems the earliest a sample could be analyzed to differentiate a geological from a biological origin.[43]

Potential sources

Possible methane sources and sinks on Mars.


The principal candidates for the origin of Mars' methane include non-biological processes such as water-rock reactions, radiolysis of water, and pyrite formation, all of which produce H2 that could then generate methane and other hydrocarbons via Fischer–Tropsch synthesis with CO and CO2.[44] It has also been shown that methane could be produced by a process involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars.[45] The required conditions for this reaction (i.e. high temperature and pressure) do not exist on the surface but may exist within the crust.[46][47] Detection of the mineral by-product serpentinite would suggest that this process is occurring. An analog on Earth suggests that low-temperature production and exhalation of methane from serpentinized rocks may be possible on Mars.[48] Another possible geophysical source could be ancient methane trapped in clathrate hydrates that may be released occasionally.[49] Under the assumption of a cold early Mars environment, a cryosphere could trap such methane as clathrates in a stable form at depth, which might exhibit sporadic release.[50]

On modern Earth, volcanism is a minor source of methane emission,[51] and it is usually accompanied by sulfur dioxide gases. However, several studies of trace gases in the Martian atmosphere have found no evidence for sulfur dioxide in the Martian atmosphere, which makes volcanism on Mars unlikely to be the source of methane.[52][53] Although geologic sources of methane such as serpentinization are possible, the lack of current volcanism, hydrothermal activity or hotspots[54] is not favorable for geologic methane.

It had also been proposed that the methane might be replenished by meteorites entering the atmosphere of Mars,[55] but researchers from the Imperial College London found that the volumes of methane released this way are too low to sustain the measured levels of the gas.[56] It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility,[57] research published in 2012 suggested that a source may be organic compounds on meteorites that are converted to methane by ultraviolet radiation.[58]

Lab tests have demonstrated that bursts of methane can be produced when an electrical discharge interacts with water ice and CO2.[59][60] The discharges from the electrification of dust particles from sand storms and dust devils in contact with permafrost ice may produce about 1.41×1016 molecules of methane per joule of applied energy.[59]

Current photochemical models cannot explain the apparent rapid variability of the methane levels on Mars.[61][62] Research suggests that the implied methane destruction lifetime is as long as ≈ 4 Earth years and as short as ≈ 0.6 Earth years.[63][64] This unexplained fast destruction rate also suggests a very active replenishing source.[65] A team from the Italian National Institute for Astrophysics suspects that the methane detected by the Curiosity rover may have been released from a nearby area called Medusae Fossae Formation located about 500 km east of Gale crater. The region is fractured and is likely volcanic in origin.[66]


Living microorganisms, such as methanogens, are another possible source, but no evidence for the presence of such organisms has been found on Mars. In Earth's oceans, biological methane production tends to be accompanied by ethane (C
) generation. The long-term ground-based spectroscopic observation did not find these organic molecules in the Martian atmosphere.[23] Given the expected long lifetimes for some of these molecules, emission of biogenic organics seems to be extremely rare or currently non-existent.[23]

The reduction of carbon dioxide into methane by reaction with hydrogen can be expressed as follows:

(∆G˚' = -134 kJ/mol CH4)

This reaction of CO2 with the hydrogen to produce methane is coupled with the generation of an electrochemical gradient across the cell membrane, which is used to generate ATP through chemiosmosis. In contrast, plants and algae obtain their energy from sunlight or O2.

Measuring the ratio of hydrogen and methane levels on Mars may help determine the likelihood of life on Mars.[67][68][69] A low H2/CH4 ratio in the atmosphere (less than approximately 40) may indicate that a large part of atmospheric methane could be attributed to biological activities,[67] but the observed ratios in the lower Martian atmosphere were "approximately 10 times" higher "suggesting that biological processes may not be responsible for the observed CH4".[67]

Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and in vitro experiments testing the growth of methanogenic bacteria on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0 wt% perchlorate salt.[70] Methanogens do not require oxygen or organic nutrients, are non-photosynthetic, use hydrogen as their energy source, and carbon dioxide (CO2) as their carbon source, so they could exist in subsurface environments on Mars.[71] If microscopic Martian life is producing the methane, it probably resides far below the surface, where it is still warm enough for liquid water to exist.[72]

Research at the University of Arkansas published in 2015 suggested that some methanogens could survive on Mars' low pressure in an environment similar to a subsurface liquid aquifer on Mars. The four species tested were Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, and Methanococcus maripaludis.[71]

A team led by Gilbert Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology of methane-producing and methane-consuming microorganisms.[4][73]

Even if rover missions determine that microscopic Martian life is the seasonal source of the methane, the life forms probably reside far below the surface, outside of the rover's reach.[74]

Potential sinks

It was initially thought that methane is chemically unstable in an oxidizing atmosphere with UV radiation and so its lifetime in the Martian atmosphere should be about 400 years,[13] but in 2014, it was concluded that the strong methane sinks are not subject to atmospheric oxidation, suggesting an efficient physical-chemical process at the surface that "consumes" methane, generically called a "sink".[75][76]

A hypothesis postulates that the methane is not consumed at all, but rather condenses and evaporates seasonally from clathrates.[77] Another hypothesis is that methane reacts with tumbling surface sand quartz (silicon dioxide SiO
) and olivine to form covalent Si – CH
bonds.[78] The researchers showed that these solids can be oxidized and gases are ionized during the erosion processes. Thus, the ionized methane reacts with the mineral surfaces and bonds to them.[79][80]


See also


  1. ^ a b Yung, Yuk L.; Chen, Pin; Nealson, Kenneth; Atreya, Sushil; Beckett, Patrick; Blank, Jennifer G.; Ehlmann, Bethany; Eiler, John; Etiope, Giuseppe (2018-09-19). "Methane on Mars and Habitability: Challenges and Responses". Astrobiology. 18 (10): 1221–1242. Bibcode:2018AsBio..18.1221Y. doi:10.1089/ast.2018.1917. ISSN 1531-1074. PMC 6205098. PMID 30234380.
  2. ^ "Making Sense of Mars' Methane". June 2008.
  3. ^ Steigerwald, Bill (15 January 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center. NASA. Retrieved 24 January 2009.
  4. ^ a b Howe, K. L.; Gavin, P.; Goodhart, T.; Kral, T. A. (2009). Methane Production by Methanogens in Perchlorate-Supplemented Media (PDF). 40th Lunar and Planetary Science Conference.
  5. ^ Levin, Gilbert V.; Straat, Patricia Ann (3 September 2009). "Methane and life on Mars". Proc. SPIE. Proceedings of SPIE. 7441 (74410D): 74410D. Bibcode:2009SPIE.7441E..0DL. doi:10.1117/12.829183. S2CID 73595154.
  6. ^ Potter, Sean (2018-06-07). "NASA Finds Ancient Organic Material, Mysterious Methane on Mars". NASA. Retrieved 2019-06-06.
  7. ^ Witze, Alexandra (2018-10-25). "Mars scientists edge closer to solving methane mystery". Nature. 563 (7729): 18–19. Bibcode:2018Natur.563...18W. doi:10.1038/d41586-018-07177-4. PMID 30377322.
  8. ^ Formisano, Vittorio; Atreya, Sushil; Encrenaz, Thérèse; Ignatiev, Nikolai; Giuranna, Marco (2004-12-03). "Detection of Methane in the Atmosphere of Mars". Science. 306 (5702): 1758–1761. Bibcode:2004Sci...306.1758F. doi:10.1126/science.1101732. ISSN 0036-8075. PMID 15514118. S2CID 13533388.
  9. ^ Mumma, M. J.; Villanueva, G. L.; Novak, R. E.; Hewagama, T.; Bonev, B. P.; DiSanti, M. A.; Mandell, A. M.; Smith, M. D. (2009-02-20). "Strong Release of Methane on Mars in Northern Summer 2003". Science. 323 (5917): 1041–1045. Bibcode:2009Sci...323.1041M. doi:10.1126/science.1165243. ISSN 0036-8075. PMID 19150811. S2CID 25083438.
  10. ^ a b c d 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. (2015-01-23) [Published online 16 December 2014]. "Mars methane detection and variability at Gale crater" (PDF). Science. 347 (6220): 415–417. Bibcode:2015Sci...347..415W. doi:10.1126/science.1261713. ISSN 0036-8075. PMID 25515120. S2CID 20304810.
  11. ^ Vasavada, Ashwin R.; Zurek, Richard W.; Sander, Stanley P.; Crisp, Joy; Lemmon, Mark; Hassler, Donald M.; Genzer, Maria; Harri, Ari-Matti; Smith, Michael D. (2018-06-08). "Background levels of methane in Mars' atmosphere show strong seasonal variations". Science. 360 (6393): 1093–1096. Bibcode:2018Sci...360.1093W. doi:10.1126/science.aaq0131. ISSN 0036-8075. PMID 29880682.
  12. ^ a b Vago, Jorge L.; Svedhem, Håkan; Zelenyi, Lev; Etiope, Giuseppe; Wilson, Colin F.; López-Moreno, Jose-Juan; Bellucci, Giancarlo; Patel, Manish R.; Neefs, Eddy (April 2019). "No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations" (PDF). Nature. 568 (7753): 517–520. Bibcode:2019Natur.568..517K. doi:10.1038/s41586-019-1096-4. ISSN 1476-4687. PMID 30971829. S2CID 106411228.
  13. ^ a b esa. "The methane mystery". European Space Agency. Retrieved 2019-06-07.
  14. ^ Etiope, Giuseppe; Oehler, Dorothy Z. (2019). "Methane spikes, background seasonality and non-detections on Mars: A geological perspective". Planetary and Space Science. 168: 52–61. Bibcode:2019P&SS..168...52E. doi:10.1016/j.pss.2019.02.001.
  15. ^ a b c d Is Mars' Methane Spike a Sign of Life? Here's How We'll Know. Daniel Oberhaus, Wired. 24 June 2019.
  16. ^ Krasnopolskya, V. A.; Maillard, J. P.; Owen, T. C. (2004). "Detection of methane in the Martian atmosphere: evidence for life?". Icarus. 172 (2): 537–547. Bibcode:2004Icar..172..537K. doi:10.1016/j.icarus.2004.07.004.
  17. ^ Formisano, V.; Atreya, S.; Encrenaz, T.; Ignatiev, N.; Giuranna, M. (2004). "Detection of Methane in the Atmosphere of Mars". Science. 306 (5702): 1758–1761. Bibcode:2004Sci...306.1758F. doi:10.1126/science.1101732. PMID 15514118. S2CID 13533388.
  18. ^ ESA Press release (2004). "Mars Express confirms methane in the Martian atmosphere". XMM-Newton Press Release. ESA: 80. Bibcode:2004xmm..pres...80. Archived from the original on 24 February 2006. Retrieved 17 March 2006.
  19. ^ a b esa. "First results from the ExoMars Trace Gas Orbiter". European Space Agency. Retrieved 2019-06-12.
  20. ^ Hand, Eric (2018). "Mars methane rises and falls with the seasons". Science. 359 (6371): 16–17. Bibcode:2018Sci...359...16H. doi:10.1126/science.359.6371.16. PMID 29301992.
  21. ^ Krasnopolsky, Vladimir A. (2006). "Some problems related to the origin of methane on Mars". Icarus. 180 (2): 359–67. Bibcode:2006Icar..180..359K. doi:10.1016/j.icarus.2005.10.015.
  22. ^ "Planetary Fourier Spectrometer website". Mars Express. ESA. Archived from the original on May 2, 2013.[verification needed]
  23. ^ a b c Villanueva, G. L.; Mumma, M. J.; Novak, R. E.; Radeva, Y. L.; Käufl, 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. 223 (1): 11–27. Bibcode:2013Icar..223...11V. doi:10.1016/j.icarus.2012.11.013.
  24. ^ Curiosity Detects Unusually High Methane Levels. Andrew Good, NASA. Press release on 23 June 2019.
  25. ^ Kerr, Richard A. (2 November 2012). "Curiosity Finds Methane on Mars, or Not". Science. Archived from the original on 5 November 2012. Retrieved 3 November 2012.
  26. ^ Wall, Mike (2 November 2012). "Curiosity Rover Finds No Methane on Mars — Yet". Retrieved 3 November 2012.
  27. ^ Chang, Kenneth (2 November 2012). "Hope of Methane on Mars Fades". The New York Times. Retrieved 3 November 2012.
  28. ^ On Mars, atmospheric methane—a sign of life on Earth—changes mysteriously with the seasons. Eric Hand, Science Magazine. 3 January 2018.
  29. ^ Webster, Christopher R.; Mahaffy, Paul R.; Atreya, Sushil K.; Flesch, Gregory J.; Farley, Kenneth A. (19 September 2013). "Low Upper Limit to Methane Abundance on Mars" (PDF). Science. 342 (6156): 355–357. Bibcode:2013Sci...342..355W. doi:10.1126/science.1242902. PMID 24051245. S2CID 43194305.
  30. ^ Cho, Adrian (19 September 2013). "Mars Rover Finds No Evidence of Burps and Farts". Science. Archived from the original on 20 September 2013. Retrieved 19 September 2013.
  31. ^ Chang, Kenneth (19 September 2013). "Mars Rover Comes Up Empty in Search for Methane". The New York Times. Retrieved 19 September 2013.
  32. ^ Webster, Guy; Neal-Jones, Nancy; Brown, Dwayne (16 December 2014). "NASA Rover Finds Active and Ancient Organic Chemistry on Mars". NASA. Retrieved 16 December 2014.
  33. ^ Chang, Kenneth (16 December 2014). "'A Great Moment': Rover Finds Clue That Mars May Harbor Life". The New York Times. Retrieved 16 December 2014.
  34. ^ Chang, Kenneth (7 June 2018). "Life on Mars? Rover's Latest Discovery Puts It 'On the Table' - The identification of organic molecules in rocks on the red planet does not necessarily point to life there, past or present, but does indicate that some of the building blocks were present". The New York Times. Retrieved 8 June 2018.
  35. ^ Webster, Christopher R.; et al. (8 June 2018). "Background levels of methane in Mars' atmosphere show strong seasonal variations". Science. 360 (6393): 1093–1096. Bibcode:2018Sci...360.1093W. doi:10.1126/science.aaq0131. PMID 29880682.
  36. ^ Eigenbrode, Jennifer L.; et al. (8 June 2018). "Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars". Science. 360 (6393): 1096–1101. Bibcode:2018Sci...360.1096E. doi:10.1126/science.aas9185. PMID 29880683. Retrieved 8 June 2018.
  37. ^ Good, Andrew; Johnson, Alana (23 June 2019). "Curiosity Detects Unusually High Methane Levels". NASA. Retrieved 23 June 2019.
  38. ^ Chang, Kenneth (22 June 2019). "NASA Rover on Mars Detects Puff of Gas That Hints at Possibility of Life - The Curiosity mission's scientists picked up the signal this week, and are seeking additional readings from the red planet". The New York Times. Retrieved 22 June 2019.
  39. ^ a b India's Mars Orbiter Mission Has a Methane Problem. Irene Klotz, Seeker, 7 December 2016.
  40. ^ Lele, Ajey (2014). Mission Mars: India's Quest for the Red Planet. Springer. ISBN 978-81-322-1520-2.
  41. ^ Global Albedo Map of Mars. ISRO. 2017-07-14
  42. ^ "The enigma of methane on Mars". European Space Agency. 2 May 2016. Retrieved 13 January 2018.
  43. ^ a b Koren, Marina (3 July 2019). "A Startling Spike on Mars - Methane gas is a potential indicator of life on the red planet, but it's proving difficult to track". The Atlantic. Retrieved 3 July 2019.
  44. ^ Mumma, Michael; et al. (2010). "The Astrobiology of Mars: Methane and Other Candinate Biomarker Gases, and Related Interdisciplinary Studies on Earth and Mars" (PDF). Astrobiology Science Conference 2010. Astrophysics Data System. Greenbelt, MD: Goddard Space Flight Center. Retrieved 24 July 2010.
  45. ^ Oze, C.; Sharma, M. (2005). "Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars". Geophys. Res. Lett. 32 (10): L10203. Bibcode:2005GeoRL..3210203O. doi:10.1029/2005GL022691.
  46. ^ Rincon, Paul (26 March 2009). "Mars domes may be 'mud volcanoes'". BBC News. Archived from the original on 29 March 2009. Retrieved 2 April 2009.
  47. ^ Team Finds New Hope for Life in Martian Crust. Western University. 16 June 2014.
  48. ^ Etiope, Giuseppe; Ehlmannc, Bethany L.; Schoell, Martin (2013). "Low temperature production and exhalation of methane from serpentinized rocks on Earth: A potential analog for methane production on Mars". Icarus. 224 (2): 276–285. Bibcode:2013Icar..224..276E. doi:10.1016/j.icarus.2012.05.009. Online 14 May 2012
  49. ^ Thomas, Caroline; et al. (January 2009). "Variability of the methane trapping in Martian subsurface clathrate hydrates". Planetary and Space Science. 57 (1): 42–47. arXiv:0810.4359. Bibcode:2009P&SS...57...42T. doi:10.1016/j.pss.2008.10.003. S2CID 1168713.
  50. ^ Lasue, Jeremie; Quesnel, Yoann; Langlais, Benoit; Chassefière, Eric (1 November 2015). "Methane storage capacity of the early martian cryosphere". Icarus. 260: 205–214. Bibcode:2015Icar..260..205L. doi:10.1016/j.icarus.2015.07.010.
  51. ^ Etiope, G.; Fridriksson, T.; Italiano, F.; Winiwarter, W.; Theloke, J. (2007-08-15). "Natural emissions of methane from geothermal and volcanic sources in Europe". Journal of Volcanology and Geothermal Research. Gas geochemistry and Earth degassing. 165 (1): 76–86. Bibcode:2007JVGR..165...76E. doi:10.1016/j.jvolgeores.2007.04.014. ISSN 0377-0273.
  52. ^ Krasnopolsky, Vladimir A (2012). "Search for methane and upper limits to ethane and SO2 on Mars". Icarus. 217 (1): 144–152. Bibcode:2012Icar..217..144K. doi:10.1016/j.icarus.2011.10.019.
  53. ^ Encrenaz, T.; Greathouse, T. K.; Richter, M. J.; Lacy, J. H.; Fouchet, T.; Bézard, B.; Lefèvre, F.; Forget, F.; Atreya, S. K. (2011). "A stringent upper limit to SO2 in the Martian atmosphere". Astronomy and Astrophysics. 530: 37. Bibcode:2011A&A...530A..37E. doi:10.1051/0004-6361/201116820.
  54. ^ "Hunting for young lava flows". Geophysical Research Letters. Red Planet. June 1, 2011. Archived from the original on October 4, 2013.
  55. ^ Keppler, Frank; Vigano, Ivan; MacLeod, Andy; Ott, Ulrich; Früchtl, Marion; Röckmann, Thomas (Jun 2012). "Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere". Nature. 486 (7401): 93–6. Bibcode:2012Natur.486...93K. doi:10.1038/nature11203. PMID 22678286. S2CID 4389735. Published online 30 May 2012
  56. ^ Court, Richard; Sephton, Mark (8 December 2009). "Life on Mars theory boosted by new methane study". Imperial College London. Retrieved 9 December 2009.
  57. ^ Court, Richard W.; Sephton, Mark A. (2009). "Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars". Earth and Planetary Science Letters. 288 (3–4): 382–5. Bibcode:2009E&PSL.288..382C. doi:10.1016/j.epsl.2009.09.041. Lay summary – (December 8, 2009).
  58. ^ Keppler, Frank; Vigano, Ivan; McLeod, Andy; Ott, Ulrich; Früchtl, Marion; Röckmann, Thomas (2012). "Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere". Nature. 486 (7401): 93–6. Bibcode:2012Natur.486...93K. doi:10.1038/nature11203. PMID 22678286. S2CID 4389735.
  59. ^ a b Robledo-Martinez, A.; Sobral, H.; Ruiz-Meza, A. (2012). "Electrical discharges as a possible source of methane on Mars: lab simulation". Geophys. Res. Lett. 39 (17): L17202. Bibcode:2012GeoRL..3917202R. doi:10.1029/2012gl053255.
  60. ^ Atkinson, Nancy. "Could Dust Devils Create Methane in Mars' Atmosphere?". Universe Today. Retrieved 2016-11-29.
  61. ^ Urquhart, James (5 August 2009). "Martian methane breaks the rules". Royal Society of Chemistry. Retrieved 20 December 2014.
  62. ^ Burns, Judith (5 August 2009). "Martian methane mystery deepens". BBC News. Retrieved 20 December 2014.
  63. ^ Mumma, Michael J.; et al. (10 February 2009). "Strong Release of Methane on Mars in Northern Summer 2003" (PDF). Science. 323 (5917): 1041–1045. Bibcode:2009Sci...323.1041M. doi:10.1126/science.1165243. PMID 19150811. S2CID 25083438.
  64. ^ Franck, Lefèvre; Forget, François (6 August 2009). "Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics". Nature. 460 (7256): 720–723. Bibcode:2009Natur.460..720L. doi:10.1038/nature08228. PMID 19661912. S2CID 4355576.
  65. ^ Burns, Judith (5 August 2009). "Martian methane mystery deepens". BBC News. Archived from the original on 6 August 2009. Retrieved 7 August 2009.
  66. ^ Giuranna, Marco; Viscardy, Sébastien; Daerden, Frank; Neary, Lori; Etiope, Giuseppe; Oehler, Dorothy; Formisano, Vittorio; Aronica, Alessandro; Wolkenberg, Paulina; Aoki, Shohei; Cardesín-Moinelo, Alejandro; Julia; Merritt, Donald; Amoroso, Marilena (2019). "Independent confirmation of a methane spike on Mars and a source region east of Gale Crater". Nature Geoscience. 12 (5): 326–332. Bibcode:2019NatGe..12..326G. doi:10.1038/s41561-019-0331-9. S2CID 134110253.
  67. ^ a b c Oze, Christopher; Jones, Camille; Goldsmith, Jonas I.; Rosenbauer, Robert J. (7 June 2012). "Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces". PNAS. 109 (25): 9750–9754. Bibcode:2012PNAS..109.9750O. doi:10.1073/pnas.1205223109. PMC 3382529. PMID 22679287.
  68. ^ Staff (25 June 2012). "Mars Life Could Leave Traces in Red Planet's Air: Study". Retrieved 27 June 2012.
  69. ^ Krasnopolsky, Vladimir A.; Maillard, Jean Pierre; Owen, Tobias C. (December 2004). "Detection of methane in the martian atmosphere: evidence for life?". Icarus. 172 (2): 537–547. Bibcode:2004Icar..172..537K. doi:10.1016/j.icarus.2004.07.004.
  70. ^ Kral, T. A.; Goodhart, T.; Howe, K. L.; Gavin, P. (2009). "Can Methanogens Grow in a Perchlorate Environment on Mars?". 72nd Annual Meeting of the Meteoritical Society. 72: 5136. Bibcode:2009M&PSA..72.5136K.
  71. ^ a b "Earth organisms survive under low-pressure Martian conditions". University of Arkansas. 2 June 2015. Archived from the original on June 4, 2015. Retrieved 2015-06-04.
  72. ^ Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center. NASA. Archived from the original on 2009-01-16. If microscopic Martian life is producing the methane, it probably resides far below the surface, where it's still warm enough for liquid water to exist
  73. ^ Levin, Gilbert V.; Straat, Patricia Ann (2009). "Methane and life on Mars". In Hoover, Richard B; Levin, Gilbert V; Rozanov, Alexei Y; Retherford, Kurt D (eds.). Instruments and Methods for Astrobiology and Planetary Missions XII. Instruments and Methods for Astrobiology and Planetary Missions Xii. 7441. pp. 12–27. Bibcode:2009SPIE.7441E..0DL. doi:10.1117/12.829183. ISBN 978-0-8194-7731-6. S2CID 73595154.
  74. ^ Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center. NASA. Archived from the original on 2009-01-17.
  75. ^ Aarhus University (2 July 2019). "Methane vanishing on Mars: Danish researchers propose new mechanism as an explanation - An interdisciplinary research group from Aarhus University has proposed a previously overlooked physical-chemical process that can explain the rapid disappearance of methane from Mars' atmosphere". EurekAlert!. Retrieved 2 July 2019.
  76. ^ Aoki, Shohei; Guiranna, Marco; Kasaba, Yasumasa; Nakagawa, Hiromu; Sindoni, Giuseppe (1 January 2015). "Search for hydrogen peroxide in the Martian atmosphere by the Planetary Fourier Spectrometer onboard Mars Express". Icarus. 245: 177–183. Bibcode:2015Icar..245..177A. doi:10.1016/j.icarus.2014.09.034.
  77. ^ Zahnle, Kevin; Freedman, Richard; Catling, David (2010). "Is there Methane on Mars? – 41st Lunar and Planetary Science Conference" (PDF). Retrieved 26 July 2010. Cite journal requires |journal= (help)
  78. ^ Jensen, Svend J. Knak; Skibsted, Jørgen; Jakobsen, Hans J.; Kate, Inge L. ten; Gunnlaugsson, Haraldur P.; Merrison, Jonathan P.; Finster, Kai; Bak, Ebbe; Iversen, Jens J.; Kondrup, Jens C.; Nørnberg, Per (2014). "A sink for methane on Mars? The answer is blowing in the wind". Icarus. 236: 24–27. Bibcode:2014Icar..236...24K. doi:10.1016/j.icarus.2014.03.036.
  79. ^ Thøgersen, Jan; et al. (22 June 2019). "Light on windy nights on Mars: A study of saltation-mediated ionization of argon in a Mars-like atmosphere". Icarus. 332: 14–18. Bibcode:2019Icar..332...14T. doi:10.1016/j.icarus.2019.06.025.
  80. ^ Saltation may be contributory in the depletion of methane on Mars. Per Nørnberg, Jan Thøgersen, Ebbe Nordskov Bak, Kai Finster, Hans Jørgen Jacobsen, and Svend J. Knak Jensen. Geophysical Research Abstracts. Vol. 21, EGU2019-13986, 2019. EGU General Assembly 2019.