For the first time in the history of space exploration, scientists measure the seasonal changes in gases that fill the air just above the surface of Mars' Galle Crater. As a result, they noticed something disturbing: oxygen, the gas that many terrestrial creatures use to breathe, is behaved in ways that scientists have not yet been able to explain through known chemical processes.
For three years on Mars (or nearly six Earth years), an instrument at the portable Mars Chemical Sampling Laboratory (SAM) inside the abdomen of a NASA Curiosity boat is breathing in Galle Crater's air and analyzing its composition. SAM sputtering results confirmed the composition of the Martian atmosphere at the surface: 95% by volume of carbon dioxide (CO 2 ), 2.6% molecular nitrogen (N 2 ), 1
In this environment, scientists find that nitrogen and argon follow a predictable seasonal pattern, waxing and decreasing in concentration at Galle Crater throughout the year, depending on how much CO 2 is in the air. They expected oxygen to do the same. But it didn't. Instead, the amount of gas in the air rose by as much as 30% in the spring and summer, and then dropped to levels predicted by known chemistry in the fall. This pattern is repeated every spring, though the amount of oxygen added to the atmosphere varies, suggesting something produces it and then consumes it.
"The first time we saw him was just mind-blowing," said Sushil Atreia, a professor of climate and space science at the University of Michigan at Ann Arbor. Atreia co-authored an article on this topic, published November 12 in Journal of Geophysical Research: Planets.
As soon as the scientists discovered the oxygen conundrum, Mars specialists began to work, trying to explain it. They first double and triple check the accuracy of the SAM instrument they used to measure gases: a quadrupole mass spectrometer. The tool was fine. They consider the ability of CO 2 or water (H 2 O) molecules to release oxygen when disintegrated into the atmosphere, resulting in a short rise. But it would take five times as much water over Mars to produce the extra oxygen, and CO (19459014] 2 decomposes too slowly to generate it in such a short time. How about reducing oxygen? is solar radiation splitting oxygen molecules into two atoms that have exploded into space? No, scientists have concluded, since it will take at least 10 years for oxygen to disappear through this process.
"We are struggling to explain this, "says Melissa Trainer, a planetary scientist at NASA's Goddard Space Flight Center in Greenbel t, Maryland, who led this study. "The fact that oxygen behavior does not repeat itself perfectly every season makes us think that this is not a problem with the dynamics of the atmosphere. There must be some chemical source and sinking, which we still cannot account for. " For scientists studying Mars, the history of oxygen is curiously similar to that of methane. Methane is constantly found in the air inside Galle Crater in such small quantities (0.00000004% on average ) that is barely detectable even by M's most sensitive instruments ars. Still, it was measured with an SAM adjustable laser spectrometer. The tool revealed that as methane rises and falls seasonally, it increases in abundance by about 60% during the summer months for unexplained reasons. (In fact, methane is also randomly dropped and dramatic. Scientists are trying to figure out why.)
With the new discoveries of oxygen in his hand, the Coach team wonders if chemistry similar to natural seasonal variations of methane can also propel oxygen. At least occasionally, the two ranges seem to be in tandem.
"We are beginning to see this excruciating dependence on methane and oxygen for much of the year of Mars," Atreia said. "I think there's something about it. I just don't have the answers yet. Nobody does."
Oxygen and methane can be produced both biologically (for example from germs) and abiotic (from water and rock chemistry). Scientists are considering all options, though they have no convincing evidence of Mars' biological activity. Curiosity has no tools that can definitively say whether Mars' methane or oxygen source is biological or geological. Scientists expect that non-biological explanations are more likely and they work hard to fully understand them.
The coach's team considers Martian soil as a source of supplemental oxygen in the spring. It is ultimately known to be rich in the element in the form of compounds such as hydrogen peroxide and perchlorates. A Viking experiment showed decades ago that heat and humidity could release oxygen from Martian soil. But this experiment took place in conditions quite different from the Martian spring environment, and did not explain the drop in oxygen, among other problems. Other possible explanations have not yet been added. For example, high-energy soil radiation can produce an additional amount of O 2 in the air, but it will take millions of years to accumulate enough oxygen in the soil to account for the gain measured in just one spring, researchers report in their article.
"We have not yet been able to devise a process that produces the required amount of oxygen, but we think it must be something in the soil surface that changes seasonally because there are not" enough oxygen atoms in the atmosphere to created the behavior we see, "says Timothy McConchy, a research assistant at the University of Maryland College College and another co-author of the article.
The only previous spacecraft with instruments capable of measuring the composition of Martian air near the ground were the NASA twins that arrived on the planet in 1976. However, the Viking experiments covered only a few Martian days, so they could not I do not detect seasonal patterns of different gases. The new SAM measurements are the first to do this. The SAM team will continue to measure atmospheric gases so scientists can collect more detailed data each season. Meanwhile, Coach and her team hope other Mars experts will work to resolve the oxygen mystery.
"This is the first time we have seen this interesting behavior in many years. We don't fully understand it, ”Coach said. "To me, it's an open call to all smart people who are interested in this: See what you can think of."
A step closer to solving the methane mystery of Mars
Melissa G. Trainer et al. Seasonal changes in atmospheric composition as measured in Gale Crater, Mars, Journal of Geophysical Research: Planets (2019). DOI: 10.1029 / 2019JE006175
NASA's Gosdard Space Flight Center
With Mars's methane secret undisclosed, Curiosity Serves Scientists New: Oxygen (2019, November 12)
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