There's not much air on Mars – atmospheric pressure is less than a hundredth of what we breathe on Earth – but what little it has is clueless planetary scientists.
Oxygen, which represents about 0.13 percent of the Martian atmosphere, is the latest mystery.
In a newspaper published this month in the Journal of Geophysical Research: Planets, scientists working with data collected in a curious NASA vehicle reported that oxygen levels unexpectedly varied depending on the seasons of Mars, at least in the neighborhood, which curiosity
This stems from the fact that earlier this year, after a rover reading, there was a large explosion of methane, another gas emitted on Earth by living things, which disappeared almost immediately.
"It's confusing, but exciting," said Sushil K. Atreya, professor of climate and space science at the University of Michigan, working on Atmospheric Curiosity Measurements. "That keeps us on our feet." Mars is certainly not boring. "
The Mars year lasts 687 days, so scientists studying oxygen variations were able to investigate behavior for nearly three Martian years until December 2017.
Oxygen Level " It rises relatively higher in spring, "Melissa said G. Trainer, research fellow at NASA's Goddard Space Flight Center in Greenbelt, MD, and lead author of the new document, "and then sinks below what we would expect later this year." “
Carbon dioxide is a major component of Martian air, and scientists have for decades understood its tides. At the poles in winter it falls out of the air and freezes on ice and then returns to the atmosphere in the spring.
High in the Martian atmosphere, ultraviolet light breaks down carbon dioxide into carbon monoxide and oxygen. atoms and then closer to earth, interactions with water release oxygen atoms into molecular pairs. Because oxygen molecules should be fairly stable and persist for about ten years, scientists expected that the number of oxygen molecules would remain almost constant
Atmospheric curiosity measurements showed exactly that pattern of nitrogen and argon, the other two trace gases in the Mars atmosphere. But for oxygen, spring concentrations were increased by a third.
"It was a very unexpected outcome, an unexpected phenomenon ," Dr. Trainer. “We don't know much about the oxygen cycle on Mars. This becomes obvious. “
The cycle was not the same every year, and scientists could not find a clear explanation – such as temperature, dust dust storms or ultraviolet radiation – which changed. from year to year.
On Earth, most of the oxygen is generated by photosynthesis of plants. But meanwhile, for scientists from Mars, it is far on the list of explanations.
"You must exclude all other processes before you go there," Atreya.
More likely sources are chemicals such as hydrogen peroxide and perchlorates known to be on Martian impurities. "It is quite clear that you need flow from the surface," Dr. Atreya. “Nothing in the atmosphere will create this kind of ascent.”
But as these chemicals can release and absorb enough oxygen to explain seasonal increase and decrease, it is difficult to detect, especially since there are only 19 oxygen measurements over five and a half years.
An interesting possibility is that the mystery of oxygen could be associated with another trace gas, methane, which also acts strangely in the Martian atmosphere.
"It is not entirely clear whether there is a correlation or not," Dr. Trainer.
Since 2003 several scientists have reported large methane explosions based on measurements from terrestrial telescopes, orbiting a spacecraft and a rover of curiosity. Other times, methane was largely absent.
The presence of methane was a surprise to scientists because the known gas generation processes are either biological – methane producing microbes – or geothermal, which would be a promising environment for life on today's Mars.
Now scientists want to know not only about how methane is formed on Mars, but how quickly it disappears. In June, the curiosity experienced a particularly strong explosion of methane – 21 ppm by volume. However, when the experiment was repeated a few days later later it came out empty – less than 1 part per billion.
The European Space Agency's Mars Express spacecraft crossed Gale Crater, instead of a rover. , only about five hours after the curiosity measured the dose – and found nothing. (The same tool confirmed a methane explosion in 2013 that observed curiosity.)
"I would say this point measured by curiosity seems very short and local," said scientist Marco Giuranna. at the Italian National Institute of Astrophysics, in charge of Mars Express.
Even between the explosions, methane on Mars is a secret. Curiosity measured the low but persistent presence of methane, approximately 410 particles per trillion, which increases and decreases over time. But the newer European circular, the ExoMars Trace Gas Orbiter, which has the ability to measure as little methane as 50 particles per trillion, has to see methane ever since it started measuring in April last year. The orbiter looks at an area a few kilometers above the ground and curiosity makes measurements on the surface. However, scientists thought that methane near the ground would be mixed in a higher atmosphere in a few weeks.
"The scientific logic puzzle is that these two lines of evidence simply cannot be reconciled," Oleg Korablev of the Space Research Institute. in Russia wrote an e-mail . dr Korablev is also the chief researcher of one of the two Trace Gas Orbiter instruments that measure methane.
Håkan Svedhem, researcher at the Trace Gas Orbiter, said: “We do not know any mechanism that can completely destroy methane in such a short time. time. It is truly a secret unless curiosity sits directly over a single local resource on the planet, and even if it does, that resource must be small. "
Scientists working on these three missions plan to close Gale Crater observations on December 15, and again in late December, Giuranna.
Four missions towards Mars are planned to begin next year. Three of them – built by NASA, China and jointly by the European Union and Russia – will try to place new levels on the planet's surface. The fourth spacecraft of the United Arab Emirates enters orbit.
However, none of them will have methane or oxygen meters.