The presence of methane in the Martian atmosphere is a fascinating puzzle for planetary scientists. This is because, on Earth, methane is related to life but can also be produced geologically. Some of the best data on Mars methane originate from the rover ios curiosity, which landed on Mars after boldly landing in the atmosphere in August 2012. Now Curious has made another intriguing discovery: the oxygen at the rover's location behaves in ways that have not yet been explained by any known atmospheric or chemical process. Gasoline levels are rising much more in the spring and summer months than anticipated, similar to the still mysterious methane. The big question, of course, is why?
The results considered by the confusing parties were published in the November 12, 2019 issue Crash for Geophysical Research: Planets.
Sushil Atrea, a professor of climate and space science at the University of Michigan, said:
The first time we saw it, it was just pushing in the mind.
So just what happens?
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Curiosity analyzed the composition of the air in Crater Gale over three Mars years (about six years on Earth), using its sample analysis at the Mars Transfer Chemistry Laboratory (SAM). The results were roughly what was expected, and have been known for years: 95% carbon dioxide (CO2), 2.6% molecular nitrogen (N2), 1.9% argon (Ar), 0.16% molecular oxygen (O2) and 0.06% carbon monoxide (CO). (Methane is normal in much smaller quantities, about 0.00000004% on average).
Nitrogen and argon tend to follow a predictable pattern each year, increasing and decreasing in proportion to how much carbon dioxide there is. This is linked to the change in air pressure throughout the year, as carbon dioxide freezes like snow and ice over the planet's poles in winter, which reduces air pressure. The air pressure rises again when carbon dioxide evaporates in spring and summer.
This is where it gets weird. Scientists had expected oxygen to follow the same pattern as nitrogen and argon, but that was not the case. Oxygen levels rose much more in spring and summer – up to 30% – and then dropped to normal levels, even below, in the fall. This same process aroused ios curiosity every spring and summer.
What are the possible explanations? Researchers have looked at several possibilities, but none of them explain all the results.
Had a problem with SAM's lab? The researchers checked, but the instrument was good and working properly.
Can carbon dioxide or water molecules release oxygen when decomposed into the atmosphere due to solar radiation? Probably not, because it will take five times as much water vapor as there is to produce the amount of oxygen observed. Carbon dioxide would decompose too slowly to generate the same amount of oxygen in such a short period of time.
As for the reduction of oxygen that can be seen later, can it be caused by the solar radiation that separates the oxygen molecules? No, because it will be an even slower process, it will take up to 10 years.
The scientists involved also find it unlikely to be caused by atmospheric circulation patterns. According to Melissa Trainer, a planetary scientist at NASA's Goddard Space Flight Center (GFSC) who led the research:
We are struggling to explain this. The fact that oxygen behavior is not perfectly repetitive every season made us think that it is not a problem related to atmospheric dynamics. There has to be some chemical source and sink that we still can't count on.
As noted by Timothy McConough, an assistant researcher at the University of Maryland:
We still haven't been able to handle a process that produces the amount of oxygen we need, but we think it has to be something in the seasonally changing surface soil because there are not enough oxygen atoms in the atmosphere. the behavior we see.
The paper itself examines each of these hypotheses in more detail and how none of them adequately explains the results so far. However something it produces much more oxygen during the warmer months than it should have. Intriguingly, both oxygen and methane have been observed to vary in tandem like this at least on some occasions, suggesting that there may be a common source. As Atrea noted:
We are beginning to see this frightening correlation between methane and oxygen for much of the year on Mars. I think there's something to it. I don't have the answers yet. Nobody does that.
Earth, along with oxygen and methane, are considered biosignatures because they tend to destroy each other unless they are produced continuously and flow into the atmosphere at relatively high rates. Because of this, both gases are said to be in a state of thermodynamic imbalance.
By far, most of the oxygen and methane on Earth is generated and / or consumed by life. Could this really be what is happening on Mars? Or is there still some unknown chemistry going on? Curiosity data has shown that the background methane levels have decreased at the same time as the oxygen levels in the last half of each year, although oxygen has increased again earlier in the year of methane, and is variable from year to year. However, the larger "chic" in methane seen by Curiosity also occurred at about the same time as the increase in oxygen in the spring. What this all means is not yet clear, and more studies will be needed.
If there is really a correlation between oxygen and methane on Mars, that's it could be a potential biosignature. A previous study in 2014 by NASA's John Domagal-Goldman of the Goddard Space Flight Center found that although oxygen and methane can sometimes be produced by non-biological processes, exoplanets for example, but finding them together would be more convincing biosignature:
However, our research reinforces the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life. We tried really, really hard to make false positive signals for life, and we found a few, but only for oxygen, ozone or methane per se.
These unusual oxygen-level fluctuations in the Gale Crater – possibly linked to fluctuations in methane and spikes – are a fascinating new mystery for Mars scientists to try and solve. As the coach mentioned:
This is the first time we have seen this interesting behavior over many years. We don't totally understand it. For me, this is an open call to all the smart people who are interested in this: Look what you can come up with.
Bottom line: NASA's curiosity rover has discovered unusual increases and decreases in oxygen levels in the Crater Gale. In a way, these are similar to methane fluctuations, and may even be related.
Source: Seasonal Variations in Atmospheric Composition, Measured at Kate Galle, Mars