For the first time in the history of space exploration, scientists have measured the seasonal changes in the gases filling the air directly above the surface of the Gale crater on Mars. As a result, they noticed something confusing: Oxygen, the gas with which many Earth dwellers breathe, behaves in a way that scientists have never been able to explain with any known chemical process.
Over the course of three Mars years (or nearly six Earth years), an instrument from the Sample Analysis at Mars (SAM) portable chemical laboratory in the belly of NASA's Curiosity SUV inhaled the air of Gale Crater and analyzed its composition. The results that SAM spewed out confirmed the composition of the Martian atmosphere on the surface: 95 vol% carbon dioxide (CO 2 ), 2.6% molecular nitrogen (N 2 ), 1
In this environment, scientists found that nitrogen and argon follow a predictable seasonal pattern and increase in concentration and decrease in the Gale Crater all year round in proportion to the amount of CO 2 in the air. They expected oxygen to do the same thing. But that was not the case. Instead, the amount of gas in the air rose by up to 30% in spring and summer, then dropped back to levels predicted by the known chemistry in the fall. This pattern repeated itself every spring, although the amount of oxygen added to the atmosphere was different, implying that something produced it and then took it away.
"The first time we saw this was just amazing," said Sushil Atreya, professor of climate and space sciences at the University of Michigan at Ann Arbor. Atreya is co-author of a paper on the subject that was published on November 12 in the Journal of Geophysical Research: Planets (19459016).
As soon as scientists discovered the oxygen mystery, Mars experts set to work to explain it. They first checked twice and thrice for the accuracy of the SAM instrument they used to measure the gases: the quadrupole mass spectrometer. The instrument was ok. They considered the possibility that CO 2 or water molecules (H 2 O) could have released oxygen when dissolved in the atmosphere, resulting in a short-lived increase. But it would take five times more water over Mars to produce the extra oxygen, and CO 2 decays too slowly to produce it in such a short time. What about oxygen depletion? Could solar radiation have decomposed oxygen molecules into two atoms that were blown up into space? No, scientists concluded, since it would take at least 10 years for the oxygen to disappear through this process.
"We have trouble explaining this," said Melissa Trainer, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt Maryland, who led the research. "The fact that oxygen behavior is not perfectly reproducible in every season suggests that it is not an atmospheric problem, it must be a chemical source and sink that we can not yet explain." 19659005] Strangely enough, for scientists studying Mars, the history of oxygen is similar to that of methane. Methane in Gale Crater is constantly in such small amounts in the air (averaging 0.00000004%) that it is barely noticeable even by the most sensitive instruments on Mars. Nevertheless, it was measured with the tunable laser spectrometer from SAM. The instrument showed that methane rises and falls seasonally, but increases by about 60% in the summer months for inexplicable reasons. (In fact, methane also increases randomly and dramatically, and scientists are trying to figure out why.)
Given the new oxygen discoveries, the coaching team wonders if a chemistry similar to that used to drive the natural seasonal variability of methane drives oxygen , At least occasionally, the two gases seem to fluctuate in tandem.
"We see this tantalizing correlation between methane and oxygen for much of the Martian year," Atreya said. "I think there's something in there, I just do not have any answers, nobody knows."
Oxygen and methane can be produced both biologically (for example from microbes) and abiotic (from the chemistry of water and rocks)). Scientists are considering all options, though they have no convincing evidence of biological activity on Mars. Curiosity has no tools that can definitely tell if the source of methane or oxygen on Mars is biological or geological. Scientists expect non-biological explanations to be more likely and work diligently to fully understand them.
The coaching team considered Martian soil as a source of extra oxygen in spring. It is known to be rich in elements in the form of compounds such as hydrogen peroxide and perchlorates. An experiment on the Viking countries decades ago showed that heat and moisture can release oxygen from the Martian soil. However, this experiment took place under conditions different from those of the Martian source and does not explain, among other things, oxygen depletion. Other explanations are not quite right for the time being. For example, additional energetic radiation of the soil could produce additional O 2 in the air. However, it would take a million years for enough oxygen to accumulate in the soil to account for the thrust measured in only one source. The researchers report in their work.
"We still could not develop a process that produces the amount of oxygen we need, but we think it has to be something in the surface soil that changes seasonally because there are none." There are not enough oxygen atoms in Available to the atmosphere to create the behaviors we see, "said Timothy McConnochie, a senior research associate at the University of Maryland at College Park and co-author of the work Curiosity Helps Scientists Develop a New: Oxygen ” title=”Credit: Melissa Trainer/Dan Gallagher/NASA Goddard”/>