# The Mars methane puzzle > NASA's Curiosity rover has measured methane at Gale crater for over a decade: a background of about 0.4 parts per billion, higher at night, and… Source: https://mysteriesdept.com/mysteries/mars-methane Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-27T17:47:46+00:00 --- **MYS** 0D7EXRJT3793·Mystery · signal # The Mars methane puzzle **0** [Follow][Ask a question](https://mysteriesdept.com/questions/key-questions?mystery=mars-methane) The Mars methane puzzle ![Photograph: The Mars methane puzzle](https://mysteriesdept.com/media/folio/mars-methane-lead) NASA/JPL-Caltech, SAM/GSFC · NASA media (generally not copyrighted; check the credit line) Rover background 0.41 ± 0.16 ppbv mean, varying 0.24–0.65 ppbv (2012–2017)⁠[[6]] Largest spike 20.5 ± 4 ppbv, June 2019⁠[[7]] Day versus night 0.05 ± 0.22 ppbv by day against 0.52 ± 0.10 ppbv at night, same season⁠[[7]] Orbital limit About 20 pptv annual mean of best limits, 640 occultations over 1.44 Mars years⁠[[10]] Instrument Tunable Laser Spectrometer of the SAM suite on Curiosity, Gale crater⁠[[5]] Latest April 2025 re-analysis proposes leaks from the instrument's foreoptics chamber⁠[[12]] Status Unexplained Questions 0 of 5 answered People [**David C. Catling** University of Washington; co-author of the statistical and instrumental critiques](https://mysteriesdept.com/mysteries/mars-methane/people/FIG0D7EXSA851ME/david-c-catling)[**Kevin Zahnle** NASA Ames; co-author of the 2011 and 2025 critiques](https://mysteriesdept.com/mysteries/mars-methane/people/FIG0D7EXSJ27CS1/kevin-zahnle)[**Sébastien Viscardy** Royal Belgian Institute for Space Aeronomy; lead author of the 2025 re-analysis](https://mysteriesdept.com/mysteries/mars-methane/people/FIG0D7EXS2E0XQW/sebastien-viscardy)[**Christopher R. Webster** JPL; lead of the TLS methane measurements](https://mysteriesdept.com/mysteries/mars-methane/people/FIG0D7EXRTM292B/christopher-r-webster) Catalog key**MYS** 0D7EXRJT3793 Methane on Mars matters because on Earth more than 90 per cent of atmospheric methane is made by living things and the rest by geochemistry⁠[[1]]. Sunlight destroys it slowly, so on Mars, standard photochemistry gives it a lifetime of centuries, long enough to spread evenly around the planet⁠[[2]]. Any methane that comes and goes, or is found in one place and not another, needs both a source and an unknown fast sink. Reports began in 2004. The Planetary Fourier Spectrometer on Mars Express found about 10 parts per billion on average, varying over the planet⁠[[3]], and telescopes on Earth reported plumes of thousands of tonnes in 2003⁠[[1]]. These claims were questioned⁠[[4]]. From 2012 Curiosity's Tunable Laser Spectrometer measured methane directly in air drawn into the rover at Gale crater: a background of a few tenths of a part per billion, a seasonal cycle, higher values at night, and spikes of 7 and later 20 parts per billion⁠[[5]]⁠[[6]]⁠[[7]]. The ExoMars Trace Gas Orbiter, whose objectives include the search for methane⁠[[8]], has looked since 2018 with two spectrometers whose limits are 10 to 100 times below the earlier detections, and has found nothing, to a limit of about 20 parts per trillion, a twentieth of Curiosity's background⁠[[9]]⁠[[10]]. If both are right, methane must seep out near the surface at night and vanish within the day, by a process not known⁠[[11]]⁠[[7]]. If the rover is wrong, the detections are an artefact of the instrument: a 2025 re-analysis found methane in the instrument's foreoptics chamber thousands of times the reported atmospheric levels, enough to explain the readings by tiny leaks⁠[[12]]. Of the 5 questions on this site, 0 are answered. ### Key questionsset by the editors [**If the methane is real, where does it come from?** ](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXXF26RFA/if-the-methane-is-real-where-does-it-come-from)No answer ahead yet [**Is there methane in the air at Gale crater?** ](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXWQM6TWB/is-there-methane-in-the-air-at-gale-crater)No answer ahead yet [All 5 questions ](https://mysteriesdept.com/questions/key-questions?mystery=mars-methane) ## What happened The early detections were remote. Mars Express reported 10 ± 5 ppbv as a global average, ranging from 0 to 30 ppbv⁠[[3]]. Ground-based infrared spectroscopy reported methane the same year⁠[[13]] and, in a 2009 paper on 2003 data, plumes from discrete regions, the largest holding about 19,000 tonnes⁠[[1]]. Lefèvre and Forget showed that such variations are incompatible with known chemistry unless methane lasts under 200 days, 600 times shorter than predicted⁠[[2]]. [![Ground-based infrared spectra of Mars, 2003 (IRTF CSHELL and Keck NIRSPEC)](https://mysteriesdept.com/files/v/55e93d785dacf720802e2ecbfaca09f93909b8f974ffa30e1895e48b219e2a95/w800)](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY9DW6Z79/ground-based-infrared-spectra-of-mars-2003-irtf-cshell-and) Ground-based infrared spectra of Mars, 2003 (IRTF CSHELL and Keck NIRSPEC)NASA/Trent Schindler, 2003. Public domain[Artifact ](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY9DW6Z79/ground-based-infrared-spectra-of-mars-2003-irtf-cshell-and) Curiosity landed in Gale crater in August 2012. Its first 20 months gave a background of 0.69 ± 0.25 ppbv and four measurements over 60 sols averaging 7.2 ± 2.1 ppbv⁠[[5]]. Five years of data gave a background of 0.41 ± 0.16 ppbv with a seasonal cycle⁠[[6]]. The Trace Gas Orbiter began science operations in 2018; its first months found no methane, to about 0.05 ppbv⁠[[9]]. In June 2019 Curiosity recorded its largest spike, 20.5 ± 4 ppbv, and in the same season found methane at night but not by day⁠[[7]]. The orbiter's limit fell to about 20 pptv by 2021⁠[[10]]. In April 2025 Viscardy, Catling and Zahnle published a re-analysis questioning the rover's detections⁠[[12]]. ### Timeline **Timeline** Squeezed where little happened. Each mark is a published claim, by how it stands:AcceptedMost likelyStill possibleDisputedRuled out ## The accounts The rover's record is presented by the TLS team in a series of papers that report every measurement with its enrichment protocol and confidence interval⁠[[5]]⁠[[6]]⁠[[7]]. The team has also answered objections, for example showing that ozone cannot be mistaken for methane at the instrument's resolution⁠[[14]]. The orbital record is presented by the ACS and NOMAD teams⁠[[9]]⁠[[10]]. The sceptical accounts are by Zahnle, Catling and colleagues, from the 2011 critique of the remote detections to the 2025 critique of the rover data⁠[[4]]⁠[[15]]⁠[[12]]. ## What was recorded Curiosity's Tunable Laser Spectrometer measures methane absorption in a sample cell filled with Martian air, either directly or after enrichment, in which carbon dioxide is removed by a scrubber to concentrate methane about 25 times⁠[[14]]. Each measurement fits three closely spaced lines (the R3 triplet)⁠[[12]]. The SAM data are archived in the Planetary Data System, with raw products held but not formally certified and derived products released in numbered batches, the latest covering sols up to March 2026⁠[[16]]. [![Curiosity SAM-TLS methane measurements, Gale crater](https://mysteriesdept.com/files/v/cbe3617943428cff56c478813d094971528826ee8a20997d1922f62ae5ab1e51/w800)](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY7Z04A03/curiosity-sam-tls-methane-measurements-gale-crater) Curiosity SAM-TLS methane measurements, Gale craterNASA/JPL-Caltech, 2012. Public domain[Artifact ](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY7Z04A03/curiosity-sam-tls-methane-measurements-gale-crater) The Trace Gas Orbiter records solar occultations: spectra of sunlight passing through the atmosphere at the limb; its limits apply above a few kilometres from the surface⁠[[10]]⁠[[11]]. Its NOMAD calibrated data are in ESA's Planetary Science Archive; ACS data there are raw only⁠[[8]]. The Mars Express PFS spectra behind the 2004 detection and the 2019 coincidence with a rover spike are in the same archive⁠[[17]]⁠[[18]]. The 2025 re-analysis drew on housekeeping data and unreported experiments as well as published spectra. It found that the foreoptics chamber, through which the laser passes before the sample cell, typically held methane three to four orders of magnitude above the levels reported for the cell, with unexpected pressure changes⁠[[12]]. In five experiments with fuller data, the three triplet lines gave discrepant methane values, with a probability of about one in a thousand if the errors were as reported⁠[[12]]. ## The explanations Local seepage with a fast sink is the explanation that keeps both records. Methane seeps from the ground at a low steady rate; at night, when the air near the surface is stable and the crater's winds converge, it builds up within metres of the ground where the rover samples it; by day, mixing dilutes it below the rover's limit and the orbiter, which sees only higher layers, never detects it⁠[[11]]⁠[[7]]. The day-night difference measured in 2019 supports this⁠[[7]]. It does not remove the problem: if seepage is widespread, the methane must still be destroyed or locked away far faster than any known process does, or the orbiter would see it accumulate⁠[[7]]⁠[[10]]⁠[[11]]. Transport modelling finds that air in the crater mixes in about a sol, so measurement timing matters⁠[[19]]. [![ExoMars Trace Gas Orbiter solar-occultation spectra (ACS and NOMAD)](https://mysteriesdept.com/files/v/3328f2c867ab0628e3bd69713fe8c88c9ac50b7d0189421ed9f86527c37dd773/w800)](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EYA5A2BZF/exomars-trace-gas-orbiter-solar-occultation-spectra-acs-and) ExoMars Trace Gas Orbiter solar-occultation spectra (ACS and NOMAD)ESA, 2018. CC BY-SA 3.0 IGO[Artifact ](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EYA5A2BZF/exomars-trace-gas-orbiter-solar-occultation-spectra-acs-and) Instrumental artefact is the explanation that keeps the orbiter's record and drops the rover's. Viscardy and colleagues estimate that leaks of less than 0.1 per cent of the foreoptics methane into the sample cell would produce the reported atmospheric levels and would not show in the housekeeping data, and that the way the three triplet lines are averaged understates the uncertainty⁠[[12]]. An earlier statistical analysis found the data as a whole not consistent with a seasonal cycle⁠[[15]]. The rover team has rejected specific confusions, such as ozone⁠[[14]], and reported day-night differences that a constant leak would not obviously produce⁠[[7]]. If the methane is real, its source could be geological, such as gas from water-rock reactions or old reservoirs escaping through seeps, or biological, such as microbes below the surface⁠[[20]]⁠[[21]]. The abundances measured so far do not distinguish them⁠[[20]]. ### Published claims **Published claims and their status** | Year | Who | Claimed | Status | Reason | |---|---|---|---|---| | 2004 | Vittorio Formisano and the Mars Express PFS team⁠[3] | Mars's atmosphere holds about 10 parts per billion of methane on average, varying from 0 to 30 over the planet. | Disputed | The Trace Gas Orbiter, 10 to 100 times more sensitive, finds none, and critics doubt the early detections were secure⁠[9]⁠[4]. | | 2004 | Vladimir Krasnopolsky and colleagues⁠[13] | Telescope spectra from Earth show methane in the Martian atmosphere, which could point to life. | Disputed | Ground-based detections must separate Martian lines from Earth's own methane, which critics say was not done securely⁠[4]. | | 2009 | Michael Mumma and colleagues⁠[1] | In northern summer 2003, plumes of methane holding up to about 19,000 tonnes rose from discrete regions of Mars. | Disputed | Never repeated, and criticised for its handling of telluric methane; the orbiter now sets limits far below it⁠[4]⁠[10]. | | 2009 | Franck Lefèvre and François Forget⁠[2] | The reported variations in Martian methane require it to be destroyed 600 times faster than known chemistry allows. | Accepted | No known sink has been found that is fast enough, which is why variable methane remains hard to explain⁠[11]. | | 2011 | Kevin Zahnle, Richard Freedman and David Catling⁠[4] | None of the telescopic or orbital methane detections made up to 2011 is secure. | Most likely | The orbiter's later non-detections fit this view, though the early detections cannot now be retested⁠[9]. | | 2015 | Christopher Webster and the Curiosity SAM team⁠[5] | Air at Gale crater carries a background of about 0.7 ppbv of methane, with an episode of about 7 ppbv over 60 sols. | Disputed | Orbital limits are far lower, and a 2025 re-analysis argues the readings may come from methane leaking inside the instrument⁠[10]⁠[12]. | | 2018 | Christopher Webster and the Curiosity SAM team⁠[6] | Background methane at Gale rises and falls with the seasons, from about 0.24 to 0.65 ppbv. | Disputed | A statistical re-analysis found the data as a whole not consistent with a seasonal cycle⁠[15]. | | 2018 | Yuk Yung and colleagues⁠[20] | Geological, geochemical and biological processes could each produce the methane Curiosity reports, and specific measurements could tell them apart. | Still possible | None of the discriminating measurements, such as carbon isotopes or companion gases, has yet been made⁠[20]. | | 2019 | Oleg Korablev and the ExoMars TGO team⁠[9] | The Trace Gas Orbiter found no methane in its first months, to a limit of about 0.05 ppbv. | Accepted | Confirmed by two instruments and tightened to 20 pptv over 1.44 Mars years⁠[10]. | | 2019 | Marco Giuranna and colleagues⁠[18] | Mars Express saw methane over Gale a day after a Curiosity spike in June 2013, from a source east of the crater. | Still possible | A single coincident detection from an instrument whose earlier readings are disputed; no later orbital detection has matched it⁠[9]. | | 2019 | John Moores and colleagues⁠[11] | Methane seeps from the ground, gathers near the surface at night and is diluted by day, which reconciles the rover and the orbiter. | Still possible | It still needs an unknown fast sink, and the rover's night readings it rests on are themselves questioned⁠[11]⁠[12]. | | 2019 | Giuseppe Etiope and Dorothy Oehler⁠[21] | Gas seepage of the kind seen on Earth could produce Mars's spikes, seasonal background and orbital non-detections. | Still possible | An argument by analogy; no seep has been located on Mars⁠[21]. | | 2020 | Edward Gillen, Paul Rimmer and David Catling⁠[15] | The Curiosity data show no strong seasonal cycle beyond what noise or random variation would produce. | Disputed | The enriched measurements alone fit a seasonal or a random pattern equally, so the dispute with the rover team stands⁠[15]. | | 2020 | Christopher Webster and the Curiosity SAM team⁠[14] | Ozone cannot be mistaken for methane in the rover's measurements at the instrument's resolution. | Accepted | Not challenged; the later critique turns on leaks in the instrument, not on ozone⁠[12]. | | 2021 | Christopher Webster and the Curiosity SAM team⁠[7] | Methane at Gale is present at night but not by day, and reached 20.5 ppbv in June 2019. | Disputed | The orbiter cannot see the surface layer at night, but the 2025 re-analysis questions the rover readings themselves⁠[12]. | | 2021 | Franck Montmessin, Oleg Korablev and the ACS team⁠[10] | Over 1.44 Mars years the atmosphere above a few kilometres holds less than 20 parts per trillion of methane. | Accepted | Consistent with the earlier ACS and NOMAD non-detections and not contested⁠[9]. | | 2025 | Sébastien Viscardy, David Catling and Kevin Zahnle⁠[12] | Methane in the rover's foreoptics chamber, thousands of times the reported atmospheric level, could explain the detections through tiny leaks. | Still possible | A 2025 critique not yet tested on the instrument; no published reply from the rover team was found in October 2026⁠[12]. | ## What would settle it The 2025 paper proposes a two-step experiment on Curiosity's instrument that would test whether methane leaks from the foreoptics chamber into the sample cell; its result would decide the artefact reading directly. A second, independent instrument measuring methane at the surface at night, at Gale or elsewhere, would test the seepage reading. From orbit, occultations or nadir observations reaching the lowest kilometre at night would test whether methane builds up near the ground. A measurement of the methane's carbon and hydrogen isotopes, if it is real, would point towards a geological or a biological source. ## Questions 0 of 5 questions are answered. **Key questions** [All 5](https://mysteriesdept.com/questions/key-questions?mystery=mars-methane) **0** [If the methane is real, where does it come from?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXXF26RFA/if-the-methane-is-real-where-does-it-come-from) 0 of 1 sub-questions answered·0 Open: 3 answers, none ahead **0** [Is there methane in the air at Gale crater?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXWQM6TWB/is-there-methane-in-the-air-at-gale-crater) 0 of 2 sub-questions answered·0 Open: 3 answers, none ahead ## Evidence 19 findings [Is there methane in the air at Gale crater?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXWQM6TWB/is-there-methane-in-the-air-at-gale-crater)9 findings [Methane is present near the surface at Gale at a background of a few tenths of a ppbv, with occasional…](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EXXYP7TFK/methane-is-present-near-the-surface-at-gale-at-a-background)Disputed +[Background 0.41 ± 0.16 ppbv over five years with spikes of about 7 ppbv.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXY6G39D8/background-0-41-0-16-ppbv-over-five-years-with-spikes-of)Supported +[Night-time values of 0.52 ± 0.10 ppbv against daytime 0.05 ± 0.22 ppbv in the same season.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXYEA5KCC/night-time-values-of-0-52-0-10-ppbv-against-daytime-0-05-0)Supported +[Ozone cannot be confused with methane at TLS resolution.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXYP45B8Y/ozone-cannot-be-confused-with-methane-at-tls-resolution)Supported +[Mars Express PFS recorded methane over the Gale region a day after a rover spike in 2013.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXYXY5XM0/mars-express-pfs-recorded-methane-over-the-gale-region-a-day)Suggestive −[The foreoptics chamber held methane three to four orders of magnitude above the sample cell; leaks under 0.1 per cent would explain the readings.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXZ5R0DK1/the-foreoptics-chamber-held-methane-three-to-four-orders-of)Suggestive −[Triplet-line discrepancies in five experiments have a probability of about 10⁻³ under the reported errors, indicating unaccounted systematics.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXZDJ40GJ/triplet-line-discrepancies-in-five-experiments-have-a)Suggestive [The rover's methane readings are an instrumental artefact, chiefly methane leaking from the foreoptics…](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EXZNC60BA/the-rovers-methane-readings-are-an-instrumental-artefact)Still possible +[Unreported diffusion experiments give a gas-transport coefficient that makes small leaks plausible.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EXZX64X5N/unreported-diffusion-experiments-give-a-gas-transport)Suggestive +[The orbiter's limits near Gale are up to four times below the rover's background for the same season.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY0500VW6/the-orbiters-limits-near-gale-are-up-to-four-times-below-the)Supported −[A strong day-night difference is not an obvious product of a leak.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY0CT140X/a-strong-day-night-difference-is-not-an-obvious-product-of-a)Speculative [If the rover is right, why does the orbiter see no methane?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXWZE752X/if-the-rover-is-right-why-does-the-orbiter-see-no-methane)3 findings [Methane seeps from the ground, is trapped near the surface at night, diluted by day, and removed by an…](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY0WE0WAD/methane-seeps-from-the-ground-is-trapped-near-the-surface-at)Still possible +[The day-night difference measured in 2019 fits night-time containment.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY1481209/the-day-night-difference-measured-in-2019-fits-night-time)Supported +[A steady seepage of 1.5 × 10⁻¹⁰ kg m⁻² per sol reconciles the data if only about 2.7 × 10⁴ km² emits, or if a fast sink exists.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY1C20SFP/a-steady-seepage-of-1-5-1010-kg-m2-per-sol-reconciles-the)Suggestive −[Standard photochemistry gives methane a lifetime of centuries; local variations need a loss 600 times faster.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY1KW48TA/standard-photochemistry-gives-methane-a-lifetime-of)Established [Does the background follow a seasonal cycle?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXX785WEM/does-the-background-follow-a-seasonal-cycle)2 findings [Background methane varies seasonally from about 0.24 to 0.65 ppbv.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY23G5D79/background-methane-varies-seasonally-from-about-0-24-to-0-65)Disputed +[A strong, repeatable seasonal variation over five years, larger than predicted from known processes.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY2BA435M/a-strong-repeatable-seasonal-variation-over-five-years)Suggestive [The data do not show a seasonal cycle beyond what noise or stochastic variation produces.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY2K40K95/the-data-do-not-show-a-seasonal-cycle-beyond-what-noise-or)Disputed +[Gaussian-process regression finds the 2018 data as a whole not consistent with seasonal variability.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY2TY4VQ5/gaussian-process-regression-finds-the-2018-data-as-a-whole)Suggestive [If the methane is real, where does it come from?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXXF26RFA/if-the-methane-is-real-where-does-it-come-from)2 findings [Geological sources, such as gas from water-rock reactions or stored reservoirs escaping through seeps.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY3AJ5KZ0/geological-sources-such-as-gas-from-water-rock-reactions-or)Still possible +[A source region east of Gale is inferred from the 2013 PFS detection and modelling.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY3JC4CZM/a-source-region-east-of-gale-is-inferred-from-the-2013-pfs)Speculative [Microbes below the surface.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY3T60CS7/microbes-below-the-surface)Still possible +[There is no evidence of life on the surface; microbes might reside beneath it.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY4206GZS/there-is-no-evidence-of-life-on-the-surface-microbes-might)Speculative [Were the remote detections of 2003–2006 real?](https://mysteriesdept.com/mysteries/mars-methane/questions/QST0D7EXXPW2F4B/were-the-remote-detections-of-20032006-real)3 findings [Methane was present at the reported levels in 2003–2006 and has since declined or become rarer.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY4HM4YRK/methane-was-present-at-the-reported-levels-in-20032006-and)Disputed +[PFS reported a global average of 10 ± 5 ppbv, varying from 0 to 30 ppbv.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY4SE56C4/pfs-reported-a-global-average-of-10-5-ppbv-varying-from-0-to)Suggestive +[Ground-based spectra showed plumes, the largest about 19,000 tonnes.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY5184TSS/ground-based-spectra-showed-plumes-the-largest-about-19-000)Suggestive [The early remote detections were not secure.](https://mysteriesdept.com/mysteries/mars-methane/answers/ANS0D7EY5924K5D/the-early-remote-detections-were-not-secure)Most likely +[The orbiter's 2018–2021 limits are 10 to 100 times below earlier detections.](https://mysteriesdept.com/mysteries/mars-methane/evidence/EVD0D7EY5GW7NZX/the-orbiters-20182021-limits-are-10-to-100-times-below)Suggestive ## Artifacts The films, photos, papers and objects this mystery rests on, each with its own key and its distance from the original. **Artifacts** [See all 14](https://mysteriesdept.com/mysteries/mars-methane/artifacts) Document2 steps from object [Curiosity SAM-TLS methane measurements, Gale crater](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY7Z04A03/curiosity-sam-tls-methane-measurements-gale-crater) NASA/JPL-Caltech · Public domain (US government work) Dataset1 step from object [Mars Express Planetary Fourier Spectrometer spectra](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY8Y85WFB/mars-express-planetary-fourier-spectrometer-spectra) PFS team · ESA PSA terms (acknowledge the PI and the PSA) Document2 steps from object [Ground-based infrared spectra of Mars, 2003 (IRTF CSHELL and Keck NIRSPEC)](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EY9DW6Z79/ground-based-infrared-spectra-of-mars-2003-irtf-cshell-and) Mumma and colleagues · publisher Document3 steps from object [ExoMars Trace Gas Orbiter solar-occultation spectra (ACS and NOMAD)](https://mysteriesdept.com/mysteries/mars-methane/artifacts/ART0D7EYA5A2BZF/exomars-trace-gas-orbiter-solar-occultation-spectra-acs-and) ESA · CC BY-SA 3.0 IGO [See all 14 artifacts](https://mysteriesdept.com/mysteries/mars-methane/artifacts) ## See also [ **Phosphine in the clouds of Venus** A 2020 report of phosphine gas in the clouds of Venus, not independently confirmed. ](https://mysteriesdept.com/mysteries/venus-phosphine) [ **HD 139139, the "Random Transiter"** A Sun-like star whose light dipped 28 times at random in 87 days of K2 data in 2017. ](https://mysteriesdept.com/mysteries/hd-139139-random-transiter) [ **Tabby's star (KIC 8462852)** A star in Cygnus that dimmed by up to 20 per cent at irregular times in Kepler data. ](https://mysteriesdept.com/mysteries/tabbys-star) [ **Wow! signal** A 72-second radio signal recorded by Ohio State's Big Ear telescope in August 1977. ](https://mysteriesdept.com/mysteries/wow-signal) ## References 1. 1.[Mumma, M., Villanueva, G., Novak, R. et al. 2009. Strong Release of Methane on Mars in Northern Summer 2003. Science 323(5917), 1041–1045.](https://mysteriesdept.com/sources/SRC0D7EXKER331J/strong-release-of-methane-on-mars-in-northern-summer-2003)[doi](https://doi.org/10.1126/science.1165243)cited 7 times here**SRC** 0D7EXKER331J 1. 2.[Lefèvre, F., Forget, F. 2009. Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics. Nature 460(7256), 720–723.](https://mysteriesdept.com/sources/SRC0D7EXKPJ0M3K/observed-variations-of-methane-on-mars-unexplained-by-known)[doi](https://doi.org/10.1038/nature08228)cited 2 times here**SRC** 0D7EXKPJ0M3K 1. 3.[Formisano, V., Atreya, S., Encrenaz, T. et al. 2004. Detection of Methane in the Atmosphere of Mars. 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No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations. Nature 568(7753), 517–520.](https://mysteriesdept.com/sources/SRC0D7EXMNT4W0Z/no-detection-of-methane-on-mars-from-early-exomars-trace-gas)[doi](https://doi.org/10.1038/s41586-019-1096-4)cited 6 times here**SRC** 0D7EXMNT4W0Z 1. 10.[Montmessin, F., Korablev, O., Trokhimovskiy, A. et al. 2021. A stringent upper limit of 20 pptv for methane on Mars and constraints on its dispersion outside Gale crater. Astronomy & Astrophysics 650, A140.](https://mysteriesdept.com/sources/SRC0D7EXPCG3CNM/a-stringent-upper-limit-of-20-pptv-for-methane-on-mars-and)[doi](https://doi.org/10.1051/0004-6361/202140389)cited 6 times here**SRC** 0D7EXPCG3CNM 1. 11.[Moores, J., King, P., Smith, C. et al. 2019. The Methane Diurnal Variation and Microseepage Flux at Gale Crater, Mars as Constrained by the ExoMars Trace Gas Orbiter and Curiosity Observations. 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