Content:

The end of the introduction section's wording implies that the detected methane is, in fact, being rapidly removed by an "unknown process," and the prior sentence does not indicate instrumental error as a potential cause. The "History of detections" section does not provide a citation for the UV decomposition rate of methane on Mars. This section also includes irrelevant detection measurements (such as those for methane, ethane, etc.).

The first paragraph about Curiosity is not well structured (talks about the rover not being able to distinguish between methane isotopologues before switching to the TGO with no noted connection between the two instruments), and the flow of topic into the following paragraph does not work (goes back the Curiosity after just recently denigrating the rover and having already swapped topics to the TGO, as well as bringing up the TLS only now). The TLS paragraph is decent, but does not talk about the other sources of methane that interfered with the measurements and was highly biased towards the confirmation of a methane cycle. The final paragraph includes Mars missions that will not be measuring methane and are thus irrelevant.

In the Geophysical section, they do not name the term "serpinitization," only describe the general process. Additionally, too many of the proposed mechanisms have only positive claims and no counterpoints, making them see more likely (except for the volcanism and meteoric delivery sections). The results from the dust and electrical discharge source appear to be taken too directly from the source, simply including a number without providing context (conversion of units, how much is it related to the measurements from the actual Mars missions, etc.).

Too much is included about methanogens and biogenic sources, especially given that there is currently no evidence for their presence (which is stated in the first sentence of the section). The process of methanogenesis does not need to be included, since that should already be in another, more focused, Wikipedia article. However, hypotheses about how methanogens could survive on Mars, in my opinion, could be kept (although, the lack of evidence of their presence as of yet should be emphasized).

The "Potential sinks" portion is simply too short relative to the "Potential sources" section and does not include enough support or counterpoints, especially since the rapid "consumption" of the methane is a big issue (because even if any of the sources are confirmed, the rapid loss would also require an acceptable explanation).

Overall, this article links to many Wikipedia articles, but are missing links to pages about types of spectroscopy and the observatories in the "History of detections" section.

Tone:

The writing is entirely in the present tense, even when referring to conclusions made in the 2000's, which do not necessarily hold up currently (such as the amount of methane being produced on Mars based on the Mars Express' PFS and the Earth telescopes, which is too hypothetical for a Wiki page in my opinion). Furthermore, the way the article is written is clearly biased towards there being methane on Mars, and that there is some mechanism causing the inconsistent measurements while failing to talk about potential instrumental failures. There needs to be more focus on the actual instruments and what exactly they measured and what their pitfalls were (no viewpoints regarding the data being unreliable were included).

Sources:

Neither source cited regarding the discrepancies in methane readings in the introduction mention instrumental error as a cause and instead focus on in situ causes. Overall, far too many sources are press releases, news articles, or magazine articles and not enough are the original journal articles, so much of the information is not properly supported. Additionally, critical sources were not sufficiently integrated into the article. In any case, the links used are functional.

Talk page:

There is a notice at the top of the page pointing out that part of the article is disputed. Specifically, it points out that the TGO's measurements cast doubt on the presence of methane as measured by previous instruments. This point was included, but only as a passing, one sentence note at the end of a paragraph about another instrument, despite referencing it earlier (which felt dismissive) and did not call into attention that any prior measurements could have been the result of error. Overall, the article was rated "C-class" and is included as a topic of interest for the astronomy and weather WikiProjects at a level of "mid-importance."

DCCProf agrees with my criticisms, in that they criticize the over-emphasis on explaining how methane on Mars can follow the trends observed, relying too much on older methane measurements and speculation into the seasonality of methane, rather than on the most reliable date (that from the TGO). Furthermore, they point out that some research has been misrepresented and does not properly refer to criticisms. Camil7 counters their stance with an explanation for the discrepancy between Curiosity and the TGO measurements, where methane is destroyed before reaching the orbiter. However, DCCProf counters that be pointing out the paper they cited is outdated and further includes more critical sources.

While the presence of methane in Mars’ atmosphere is still debated, it is of interest to many geologists and astrobiologists^[1] as a potential indicator of geochemical process such as hydrogeochemical activity and possibly the presence of microbial life.^[2]

Since 2004, trace amounts of methane (ranging from 60 ppbv to under detection limit (< 0.05 ppbv)) have been reported in various missions and observational studies.^{[3][4][5][6][7]} 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][8][9] Furthermore, if these periodical methane detections are accurate, they would require rapid removal from the atmosphere. However, the process through which this could occur at the necessary rates is still uncertain.^[10][8][9]

1. Own paper and published criticism

In August 2012, the Curiosity rover landed on Mars, with its landing site being Gale crater. The rover's Tunable Laser Spectrometer (TLS) was capable of making precise abundance measurements.^[11] However, as it was unable to sufficiently distinguish between the different isotopologues of methane, it was unable to determine if the detected methane was geophysical or biological in origin.^[12]

The first measurements with Curiosity's TLS, published in 2013,^[13] were from sol 79 to 313. They detected an insignificant level of methane, originally reporting an upper limit of 1.3 ppbv (where the minimum signal the TLS was designed to detect was 0.3 ppbv). However, terrestrial methane present in the foreoptics chamber reduced the accuracy of measurements up through sol 292. Contrasting these early results, four measurements taken over two months from late 2013 to early 2014 averaged at 7.2 ppbv.^[5] This approximately ten-fold 'spike' in methane then dropped back down to one tenth of that level, suggesting that Mars may be episodically producing or releasing methane from an unknown source.^[5][13] In 2018, a cyclical seasonal variation in the background level of atmospheric methane was proposed based on these results.^[6] A little over a year later, in June 2019, a spike to 21 ppbv was detected, which was the largest concentration of methane detected in situ by the Curiosity rover by that time.^[14] However, the validity of the proposed seasonal methane cycles based on these TLS results have been subject to criticism. One critique, made by Gillen et al. in 2020,^[15] casts doubt on the statistical validity of such claims by pointing out how they were based on taking sparse TLS methane measurements spanning multiple Martian years and placing them on a timeline of a single year. Their reanalysis of the data using an approach unbiased by a shorter time frame resulted in no observation of seasonal variability. Furthermore, they noted that the reported measurements have been subject to significant changes in the removal of systematic error over time, casting further uncertainty on the accuracy of the reported measurements.

2.

Research suggests that the implied methane destruction lifetime is as long as ≈ 4 Earth years and as short as ≈ 0.5 Earth years.^[4][8]

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 300 years,^[2] 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".^[16] For example, in 2009 Lefèvre and Forget^[8] suggest that strong oxidants, such as hydrogen peroxide, present in the regolith could deplete methane resulting from episodic releases in localized areas. However, they calculated that it would require the atmospheric methane interfacing with the surface to have a lifetime of less than an hour in order to necessarily keep the total atmospheric lifetime of methane below 200 days, even with highly localized methane releases, thus implying a highly oxidizing environment incongruous with the presence of complex organics and therefore life,^[8] something that does not entirely follow observations by Curiosity's gas chromatography mass spectrometer (GC-MS).^[17] An alternative and more recent explanation from Moores et al. in 2019^[9] does not require a rapid sink for methane, permitting an atmospheric lifetime of methane of 300 years. They propose that the lower methane content observed during daytime (below an upper bound of 0.05 ppbv)^[7] can be reconciled with the higher content observed during nighttime (0.41 ppbv)^[6] as the increased surface temperature during the day leads to greater convection currents, mixing and diluting the methane with the bulk atmosphere. To fit these parameters, their modeling restrains methane releases to diurnal microseepages in fluxes averaging to 1.5 x 10^-10 kg•m^-2•sol^-1 originating from 2.7 x 10⁴ km² of the Martian surface, such as from locations like Gale crater.^[9]

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