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In Nature Geoscience's article Independent confirmation of a methane spike on Mars and a source region east of Gale Crater is announced that the reported methane spike on sol 305 by the Tunable Laser Spectrometer-Sample Analysis at Mars (TLS-SAM) on Curiosity was confirmed by Planetary Fourier Spectrometer (PFS) observations onboard the Mars Express spacecraft in the spot-tracking mode. The combination of PFS and TLS-SAM observations strongly suggested that the emission took place outside the crater.

Using wind fields simulations with a general circulation model (GCM) and independently from this trying to find potential methane release structures around Gale crater led the authors to conclude that the Aeolis Mensae region a few hundred km east of the crater was the most likely source of the methane spike.

In this article the authors used the Mars Regional Atmospheric Modeling System for methane transport simulations and concluded that a methane source just outside Gale crater could be excluded to explain the observed methane spikes and even the lower background methane levels.

In the recent article Mars Methane Sources in Northwestern Gale Crater Inferred From Back Trajectory Modeling the authors used new modeling techniques to identify upstream methane emission regions at an unprecedented spatial resolution. The outcome supports surface emission sites in the vicinity of the Curiosity rover. Only if fast methane removal mechanisms would exist, emission sites could be outside Gale crater, most likely to the north.
From the Conclusions chapter:

Methane concentration data from future in situ measurements, especially those collected in consecutive measurements performed within a few hours, could further improve the emission site identification.

So, after having examined the sulfate unit, instead of going further up Mount Sharp, could not Curiosity turn around and head for the northern plains in Gale crater ?

Travelling just 50 m a day, while doing TLS-SAM measurements every day and/or night, it could reach the northern rim in less than 4 years.

Could the scientific value of going up Mount Sharp and that of intensive methane measurements while going north be quantified scientifically and be weighed against each other ?
And if not, could not the fact that the Curiosity rover will be the only one for a long, long time that can do in situ methane measurements on Mars be an extra motive to change to this new, main scientific objective ?

Cornelis
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    It would be cheaper, and quicker, and more likely to succeed, to design a new mission to do just that investigation and let Curiosity get on with its job. – CuteKItty_pleaseStopBArking Dec 30 '21 at 10:47
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    I tend to agree with @CuteKItty_pleaseStopBArking. Traveling 4 years to get to the supposed source of methane emissions is a long time & much can happen in that time. It's also 4 years of traveling & little ease. Does NASA have the budget for this? If Curiosity continues its existing schedule it can investigate a lot of other things & produce other data which would be useful nonetheless. – Fred Dec 30 '21 at 11:41
  • related Mars methane/rover questions: Will the Mars 2020 rover's sensitivity to methane be better than Curiosity's? and What new has come from the recent methane findings on Mars? – uhoh Dec 30 '21 at 12:33
  • I think, should NOT! Pretty tentative indications. Measured in a few parts per BILLION! And so what? There's methane everywhere, one of the simplest molecules there is. There's real planetary science to be done instead. This "hunt for life on Mars" gotta stop. – LocalFluff Dec 30 '21 at 12:35
  • @CuteKItty_pleaseStopBArking The reality is, there just will not be such a mission for a long, long time. – Cornelis Dec 30 '21 at 12:56
  • @Fred The supposed sources can be anywhere along the route to the northern plaines and rim of Gale crater, so indeed much can happen (i.e. detecting methane plumes) in that time. If NASA will have the budget to go further up Mount Sharp, why would it not have the budget for this important scientific objective ? Traveling to the north will not have to exclude operating the other instruments and produce other important data. – Cornelis Dec 30 '21 at 13:10
  • @LocalFluff This is no hunt for life at all, this is about subsurface geology. Would you like it to stop if a near surface gas field could be detected in the northern plains of Gale crater ? – Cornelis Dec 30 '21 at 13:53
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    @Cornelis Being a few parts per BILLION, rarely occasionally, I'd say that Curiosity is not suitable to make a hunt for that stuff into its main mission, but just carry on with what is was designed to do. Leave the methane issue to the ExoMars rover which will drill several meters into the ground. It might strike oil! ;-) – LocalFluff Dec 30 '21 at 14:16
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    @LocalFluff Like on Earth, subsurface methane will likely be regional, so there's a good chance the ExoMars rover will find nothing of that. The Tunable Laser Spectrmeter was designed to make a hunt for this stuff, as it did. Curiosity has the unique opportunity to do this search, meanwhile it can (occasionally) continue with using the other important instruments. – Cornelis Dec 30 '21 at 14:32

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The comments are degenerating into an opinion-fest, so I'm going with the facts: Curiosity has already been investigating methane apparently emerging from Gale Crater, finding nighttime background levels of 0.2-0.7 ppb with a peak over 20 ppb. Apparently Curiosity's data combined with that of the ESA's ExoMars orbiter are showing a diurnal cycle, with the methane appearing preferentially at night. See a more detailed description of the findings here.

Oscar Lanzi
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    From the linked article: 'Moore thinks we need more measurements from the ground. Curiosity has made about 16 measurements in a decade. "It's a very coarse data set and you can imagine it must be difficult to figure out what happens over the day if you only measure every six months ". I think since only Curiosity will be able to do such measurements on the ground for a long, long time that could justify to intensify them – Cornelis Feb 01 '22 at 23:43
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    ExoMars made a day-night-day series when the discrepancy emerged between ExoMars during the day and Curiosity during the night, leading to the finding of the daily cycle. – Oscar Lanzi Feb 01 '22 at 23:54
  • Apparently the methane case is not important enough for ESA to install a TLS on the Rosalind Franklin rover. But this rover should be able to detect carbon-bearing molecules in the subsurface where likely the methane comes from ! – Cornelis Feb 02 '22 at 11:40