Mars: Methane puzzle continues

Curiosity rover registers surprisingly high methane levels but only briefly

The methane readings of the Marsrovers Curiosity puzzle planetary scientists. © NASA / JPL-Caltech / MSSS
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Mysterious Phenomenon: Just last week, the Mars rover Curiosity measured the highest ever recorded methane level on the red planet - but now methane has disappeared. Apparently it was a temporary outgassing. However, where this gas comes from and whether it is of geochemical or biological origin still remains enigmatic.

Planetary researchers have been puzzling over the "capricious" methane of Mars for years. For while some spacecraft have detected locally and seasonally fluctuating levels of this gas in the Martian atmosphere, other, especially sensitive "snoopers" such as the ESA's Trace Gas Orbiter (TGO) have so far found nothing. This is exciting because methane is considered a potential indicator of microbial life. However, methane can also be produced geochemically, for example by the UV irradiation of rock material.

The highest ever measured methane value ...

Now, new readings are causing more confusion. The NASA Mars rover Curiosity measured surprisingly high levels of methane last week - the highest ever recorded on Mars. The laser spectrometer of the "rolling chemical laboratory" determined a value of 21 parts per billion (ppb). This concentration is 20 times higher than the background level of one ppb normally found in the Gale crater, NASA reports.

Previously, Curiosity had temporarily measured elevated methane levels in the Martian crater - in 2013. But even this peak was only one-third as high as the current one. Where this gas comes from so suddenly and how long these methane plumes last is unknown. "With our current measurements, we have no way of knowing if the source of the methane is biological or geological. We do not even know if the gas was ancient or new, "explains Paul Mahaffy of NASA's Jet Propulsion Laboratory (JPL).

... and then everything is gone

But it gets even stranger: After the surprisingly high methane value of last week, the NASA researchers let the rover perform a follow-up experiment on the weekend. This time, however, the measurement returned almost nothing: The methane value has fallen back to less than one ppb and thus almost to the background level in the Gale Crater. This makes it clear that somewhere there must have been a temporary outgassing. But where exactly can not determine Curiosity's instruments. display

A possible explanation for the mysterious appearance and disappearance of the methane peaks could be many small outgassings that cover the surface of Mars. If then each of these miniblips only occasionally ausst zut small amounts of gas, although the Rover can prove this, because he has his "nose" almost directly over the vent. For the orbital probes, however, these gas swells are too small and weak to be noticed.

"The methane riddle continues, " states Ashwin Vasavada of the JPL. "We are more motivated than ever to stick to the measurements. We want to find out how the methane gets into the Martian atmosphere and how it behaves there. "Next, the researchers now want to evaluate the readings taken by the TGO probe during the last week when flying over the Gale crater.

Source: NASA / JPL

- Nadja Podbregar