Methane, an organic molecule, is found in Earth's atmosphere. It is most commonly produced by living organisms. The most famous example being farting cows. For planetary scientists, however, it has been a strange mystery to discover that methane was found on Mars.
NASA's Curiosity rover picked up methane traces on Mars numerous times in recent years. These emissions could be due to geological processes, but it is possible that they indicate the existence of some kind of life on Mars (unlikely to include cows).
Scientists are excited about the prospect. However, data are not clear. The European Space Agency's orbiting technology has not detected methane at any concentration higher in the atmosphere.
This is strange because plumes of methane could dissolve in the Martian atmosphere. However, our instruments can still detect that hint of briny.
"[W]hen it announced that it saw no methane," Chris Webster, a NASA planetary scientist from NASA's Jet Propulsion Laboratory, said.
So what's the reason for this discrepancy? Webster and his coworkers went back to examine the data, excluding any factor that could have contributed to the discovery of methane by the rover.
Webster explained that they looked into the correlations between the pointing of a rover, ground, crushing of rocks, wheel degradation, and other factors.
"I can't overstate the amount of effort that the team put into ensuring those measurements were correct.
It turns out that the plumes of methane measured at Curiosity weren't flukes. The Sun is the reason for the disparity in measurements. The team discovered that methane found on Mars can fluctuate in flow and temperature depending on the time of the day. Curiosity's power-intensive instrument for detecting methane is best used at night.
Because the Martian atmosphere is still at night, methane doesn’t rise to the surface and diffuse into the atmosphere as it does during the heat of day. Researchers believe that the gas stays near the surface of Mars at night. However, during the day, it is diluted so that ESA's orbiting instrument (which requires sunlight) can't detect the gas at a distance.
The research team took high-precision measurements on Martian methane to confirm their prediction. This was the first time Curiosity had done so in daylight. They also measured the night in between.
The methane that was seeping into the atmosphere at night dissolved in the atmosphere, as expected.
"John [E. Moores] predicted that methane would effectively drop to zero during the day. Our two daytime measurements supported that prediction," says Paul Mahaffy, a NASA planetary scientist at NASA's Goddard Space Flight Center.
"So that's how you put to rest this huge discrepancy."
However, it's not clear why methane isn't building up over time in Martian atmosphere - the researchers believe that it should last at least 300 years before being destroyed by radiation from the Sun.
Gale crater is unlikely to be the sole source of planet-micro-seepages of methane, as Gale crater isn't very special geologically. They believe that something has to be doing something to destroy or sequester all methane from the atmosphere before it gathers.
Now, the team is testing whether there could be an excess of oxygen or dust.
While some of the mysteries may be solved, we now have more questions. Curiosity lives up to its name.
Astronomy and Astrophysics published the study.