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NASA published past June high methane concentrations were measured at Mars.

This week, NASA's Curiosity Mars rover found a surprising result: the largest amount of methane ever measured during the mission — about 21 parts per billion units by volume (ppbv).

However, this news in the spanish press surprised me today as it is titled: "There is no methane on Mars or there has been in the last 350 years".

They point to this paper about ESA Exomars, published on Nature, where they say ESA has not detected any methane:

"We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections" (Korablev et al.,2019).

In the interview, the spanish scientifist of ESA put on doubt NASA's measure:

"I would be delighted to find methane on Mars. And if it were of biological origin, better than better. But if there had been in the last 350 years, it would be all over the planet and NOMAD would have detected it. None of the Curiosity measurements is able to confirm the origin of the methane they say they have registered. What the observations made from terrestrial telescopes have detected is an asymmetry, an irregularity that they have interpreted as Martian methane. But the published measurements contradict the most elementary atmospheric physics since it is impossible that it is only concentrated in one area", warns López Moreno.

The scientist of the European and Russian team believes that it could be an error in reading the spectography or that they have not identified that the source of the gas is the Curiosity rover itself, since it can concentrate up to 1,000 times more methane than it could exist in the atmosphere.

Translation by Google from spanish article

Is it possible that Curiosity measured his own trace or failed at the spectrometry, as the ESA scientifist sugest, when NASA claimed they found methane on Mars?

-Korablev, O. et al. (2019):"No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations." Nature 568, pages 517–520

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    $\begingroup$ The swiss newspaper article nzz.ch/wissenschaft/… (in German) speculates that martian soil contains a certain amount of methane hydrate, which is released (by mechanical compression) by the rover when it drivers over a spot that has it. This very local source, combined with quick dilution in the martian atmosphere, could explain the spiky nature of the measurements and the fact that orbital detectors don't detect anything. $\endgroup$
    – Guntram Blohm
    Commented Jul 1, 2019 at 19:17
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    $\begingroup$ Similar question was posed back in 2013 about why the terrestrial based mehane observations were higher than what Curiosity was measuring from the surface: space.stackexchange.com/questions/2133/… $\endgroup$
    – Shorlan
    Commented Jul 1, 2019 at 20:45
  • $\begingroup$ @guntram interesting, but then where does the methane hydrate come from? Such questions imply that we have to look beyond the immediate mechanism to get to the bottom of the matter. $\endgroup$
    – Oscar Lanzi
    Commented Jul 1, 2019 at 20:54
  • $\begingroup$ @Oscar Lanzi. Methane clatrates can be formed inorganically. That needs water and a source of hydrolisys that can be earthquakes. The fact Mars loosed his water doesn't mean there is not CH4 on the soil. $\endgroup$
    – user32129
    Commented Jul 2, 2019 at 9:08
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    $\begingroup$ If anyone wants to read the paper that discusses this: orfeo.kbr.be/bitstream/handle/internal/7247/… $\endgroup$
    – ANone
    Commented Jul 2, 2019 at 9:28

3 Answers 3

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There's a lot to unpack here, so let's look at the various discoveries of methane on Mars.

The first discovery came from multiple groups in 2003-2004 using first Mars Express, followed by Earth based instruments. The measured amounts were small, and being from Earth, could be tricky to know for sure. Mars Global Surveyor data was studied, and it seemed to find methane on a different band, which supported the hypothesis, although they later redacted that statement, meaning that Mars Express and Curiosity are the only two spacecraft which claim detection of methane.

Curiosity has seen many times plumes of Methane from the surface. It does this via a tunable laser spectrometer, which allows it to look for the specific signature of methane in its samples.

ESA's Trace Gas Orbiter (TGO) so far hasn't seen any evidence of methane on Mars at all from orbit.

So all of this basically leads to one of a few conclusions.

  1. TGO is somehow broken, and can't detect methane at all. Unlikely.
  2. Curiosity is somehow broken, and is getting false results. Unlikely.
  3. The methane spikes are very small in nature, and TGO doesn't have the resolution to do so at all. Not very likely, as methane will spread.
  4. Some unknown mechanism is taking methane out of the atmosphere quickly, and it is produced at or near Gale Crater. There are actually a few possible sources for this, including dust devils and wind.
  5. Curiosity is the source of methane- See below.

Which one is really hard to know. TGO theoretically should be the least likely to be wrong in these measurements, but that can be tricky to know for sure. No other instrument around Mars can detect this for sure.

If Curiosity was making its own methane somehow, it would need to be coming from one of three sources:

  1. The rover does actually contain a small amount of methane, which could have gotten in the sensor, but that is too small to really account for the differences.
  2. There might be some microbes that are living on Curiosity on Mars that came from Earth, and are producing the methane.
  3. It could also be coming from the soil in the area of Curiosity as it moves over the surface of the planet.

It is worth noting that the pattern of methane detection from Curiosity is VERY strange. One would expect somewhat even levels, while Curiosity has seen lots of peaks and dips. It would almost need both a methane producer and a methane sink to account for the variations, which seems odd. It seems to be higher in some areas than others, which is strange as methane should be distributed across the surface pretty evenly.

What will help resolve this is more instruments. Of course, there are no planned instruments to help resolve this difference at the moment.

Bottom line: We don't know exactly what is going on. TGO not working seems unlikely, as it is actually detecting other trace gasses, just not methane. Curiosity is certainly detecting methane, but the source of the methane is a bit unclear. Other instruments have detected it, but near the limits of their resolution, which makes it possible they produced a false alarm. Whichever source it is, we don't really know yet, but it is certainly a curiosity!

EDIT: I did a video on this subject, which goes in to a fair bit more detail. If you REALLY want to know EVERYTHING about this, check the video out, but the basics are all in this answer.

See also:

Pro methane

Against Methane

Mixed views on Methane

Explanations for where methane is going

Others

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    $\begingroup$ "There might be some microbes that are living on Curiosity on Mars that came from Earth, and are producing the methane." What's their food source? (The carbon and hydrogen must come from somewhere, after all.) $\endgroup$
    – RonJohn
    Commented Jul 2, 2019 at 3:44
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    $\begingroup$ @Universal_learner Dr. Moreno's response still didn't really say enough to show where the issue is. If the methane spikes are highly localized, for example, the spectrometer might not have the spatial characteristics to recognize a small area with a spike. Guntram Blohm's comment, for example, seems like a very plausible explanation for why both Curiosity and the ESA have seemingly contradictory results. $\endgroup$
    – JMac
    Commented Jul 2, 2019 at 12:32
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    $\begingroup$ @Universal_learner That would made #2 on this list correct then. Small amounts of methane are released through mechanical disturbances. It's not "analytical errors". It's a lack of resolution to be able to measure those levels of methane. The rover could read them because it was generating them, and thus much closer to the methane concentrations compared to an orbiter which would be measuring over a much larger average area. $\endgroup$
    – JMac
    Commented Jul 2, 2019 at 12:49
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    $\begingroup$ @Universal_learner: But Dr. Lopez Moreno is a member of the NOMAD team, and so perhaps biased in favor of his team's results. I do have problems understanding how an orbiting sensor would have the resolution to detect small, localized releases that a rover might detect. $\endgroup$
    – jamesqf
    Commented Jul 2, 2019 at 17:10
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    $\begingroup$ I'm working on REALLY understanding this whole issue deeply, likely reading every journal article published on the matter. NOMAD is a much better instrument to detect methane then any other, and I'm getting a lot of really good information on the subject. This might take a while, but I should have something interesting in a week or so. $\endgroup$
    – PearsonArtPhoto ♦
    Commented Jul 3, 2019 at 1:13
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I am Jose Juan Lopez Moreno, co-I (co-investigator) of TGO-NOMAD and I feel obliged to respond to PearsonArtPhoto's answer.

There is something real: TGO carries 2 independent instruments with a sensitivity high enough to detect methane with a low limit of 0.05 ppbv. Those independent instruments are led by different and independent teams. They are far from being broken, they are giving extraordinary results when measuring other compounds of the Martian atmosphere at levels never before reached.

The lifetime of methane in the atmosphere of Mars is more than 300 years, hence in view of the results that ACS and NOMAD are giving we can say with full confidence that if ANY of the published measurements of the Martian methane were real, both ACS and NOMAD should have detected methane in all and each of the observations made so far. However NO DETECTION so far. Hence?

Therefore the negative results show that in the present Martian atmosphere there are no signs of methane and, with very little knowledge of atmospheric physics, we can assure that methane has not been present on Mars, at levels highest than 0.05 ppbv in the last 350 years.

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    $\begingroup$ With all due respect @JoseJuanLopwzMoreno, Curiosity's is not the first finding of methane. Mars Express found indications, ground based observations found indications as well, and now Curiosity. Understanding why Curiosity is reading methane and NOMAD isn't is what's important. Science often progresses by learning from failure, space science is no exception to this, and neither side should ignore that possibility. $\endgroup$
    – GdD
    Commented Jul 2, 2019 at 8:28
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    $\begingroup$ Thanks for that answer, but I strongly disagree with the last conclusion: "... we can assure that methane has not been present in Mars, ...". No, you can't! All you can say is, that there was no "free methane in the Martian atmosphere, given we know enough about the atmospheric physics of Mars". It sounds picky, but it's the difference between scientific facts and opinions. Do you disagree? $\endgroup$
    – Mayou36
    Commented Jul 2, 2019 at 11:48
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    $\begingroup$ I don't see how this answer is getting so many upvotes. While it does come from an authoritative source, the only concrete point being made is basically: We have two independent "zero" measurements, therefore it has to be zero, regardless of other evidence. Even RAID1 in enterprise-grade servers fail from time to time, let alone devices exposed to the radiation and vacuum of space. $\endgroup$
    – March Ho
    Commented Jul 2, 2019 at 11:53
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    $\begingroup$ What does co-l mean? Can you expand that abbreviation? $\endgroup$
    – rrauenza
    Commented Jul 2, 2019 at 18:53
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    $\begingroup$ How does this even attempt to answer the original question? It is essentially the same information that the OP doubts, coming from exactly the same source. $\endgroup$
    – Diego Sánchez
    Commented Jul 3, 2019 at 17:49
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July 2021 update: It's a daily variation, not an instrument problem

A NASA article explains that the difference between the methane measurements of Curiosity and the Trace Gas Orbiter is due to the time of day that each spacecraft performs it measurements:

Moores, as well as other Curiosity team members studying wind patterns in Gale Crater, hypothesized that the discrepancy between methane measurements comes down to the time of day they’re taken. Because it needs a lot of power, TLS operates mostly at night when no other Curiosity instruments are working. The Martian atmosphere is calm at night, Moores noted, so the methane seeping from the ground builds up near the surface where Curiosity can detect it.

The Trace Gas Orbiter, on the other hand, requires sunlight to pinpoint methane about 3 miles, or 5 kilometers, above the surface. “Any atmosphere near a planet’s surface goes through a cycle during the day,” Moores said. Heat from the Sun churns the atmosphere as warm air rises and cool air sinks. Thus, the methane that is confined near the surface at night is mixed into the broader atmosphere during the day, which dilutes it to undetectable levels. “So I realized no instrument, especially an orbiting one, would see anything,” Moores said.

This was tested by having Curiosity take a series of measurements during daytime, the following night, and the following day. The results confirmed that levels were higher at night.

Immediately, the Curiosity team decided to test Moores’ prediction by collecting the first high-precision daytime measurements. TLS measured methane consecutively over the course of one Martian day, bracketing one nighttime measurement with two daytime ones. [...]
TLS’ nighttime measurement fit neatly within the average the team had already established. “So that’s one way of putting to bed this big discrepancy,” Mahaffy said.

While this study suggests that methane concentrations rise and fall throughout the day at the surface of Gale Crater, scientists have yet to solve the global methane puzzle at Mars.

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  • $\begingroup$ However, this is completely contrary to the claim by Jose Juan Lopez Moreno above, that states that methane has a long lifetime in the Mars atmosphere and could not have been "at levels highest than 0.05 ppbv in the last 350 years". A daily emission that concentrates surface levels to 21 ppbv would quite rapidly saturate the atmosphere as a whole to levels greater than 0.05... One of the two claims is not just wrong, but completely wrong. $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 14, 2021 at 7:05
  • $\begingroup$ Curiouser & curiouser, there is a claim that the "rate of seepage of methane at Gale crater which we find equivalent to 2.8 kg per Martian day". $\endgroup$
    – Fred
    Commented Jul 14, 2021 at 10:58

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