MOSCOW (MIPT) — The quest to find methane on Mars may well be the most exciting line of research focusing on the red planet in this century. On Earth, methane is primarily produced by living beings, so its traces in the Martian atmosphere could point to the presence of life.
Alexander Rodin is an expert on planetary climates in the solar system. He heads the infrared spectroscopy lab at the Moscow Institute of Physics and Technology (MIPT) and has worked on the Mars Express and ExoMars projects. Rodin is available to comment on the recent methane spike measured by NASA’s Curiosity rover, including the following questions.
Q: Why is everyone so excited about methane on Mars?
A: Both researchers and laypeople are really intrigued, since the presence of methane would be fairly hard to explain without resorting to some biological activity. This is a psychological factor one has to bear in mind: People want to find methane on Mars.
Q: Haven’t they? Isn’t the latest measurement by Curiosity definitive?
A: I think we still cannot rule out the possibility that such methane spikes are some kind of an equipment artifact. The Earth-based, Mars-based, and orbital measurements appear contradictory.
Q: What is the main contradiction?
A: In April, Nature published a paper reporting the analysis of the first measurements by the Russian spectrometers carried on board of the ExoMars orbiter. It conducts remote sensing of the atmospheric layers that lie as low as about 35 kilometers above the ground. The equipment is geared toward detecting methane. It is some 100 times more sensitive to that gas than the instruments we had before. Here comes the contradiction: The orbiter has spotted no methane so far, or at least 100 times less compared with the spikes detected by Curiosity.
Q: Could the methane be somehow evading the orbiter?
A: The orbital spectrometer cannot penetrate into the atmospheric layer below 30 kilometers or so. That said, the way we understand the atmosphere dynamics on Mars, it would be very hard to come up with a mechanism that produces several parts per billion of methane at the surface and yet this concentration would somehow fade a hundredfold by 30 kilometers above the ground. This appears highly unlikely, because the Martian atmosphere is relatively homogeneous.
Q: Does that mean something is wrong with Curiosity’s measurements?
A: The rover samples Martian air and analyzes it in a special compartment. I realize that the process has been thoroughly scrutinized for possible flaws, but one cannot quite eliminate the possibility that some plastic component in the rover could undergo degassing under the harsh conditions of Mars. This could theoretically release gasses that could undergo a reaction producing trace amounts of methane.
Q: What about the Earth-based observations?
A: Methane on Mars was originally reported in 2003 by Russian astronomer Vladimir Krasnopolsky, at that time working in the United States, on the Canada-France-Hawaii Telescope. He reported an average methane concentration of about 8 ppb for the planet. However, by checking for possible errors, Krasnopolsky found his measurements in fact allowed for a 20% chance that there was no methane at all on Mars. In fact, he reported no methane detection in 2010.
Q: Didn’t Mars Express independently confirm the 2013 methane spike?
A: I am fairly skeptical about that. The thing is that the Planetary Fourier Spectrometer carried by Mars Express has a much lower spectral resolution than the Atmospheric Chemistry Suite onboard ExoMars’ Trace Gas Orbiter. PFS is arguably not sensitive enough to make a definitive measurement, considering the tiny concentrations involved.
So the mystery behind the transient methane plumes observed by the Martial rover Curiosity remains. Hopefully, new data coming in from the European-Russian ExoMars collaboration could shed more light on it.
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