New clues to life on Mars? Curiosity detects mysterious methane spikes

Tuesday, December 16, 2014, 4:53 PM - NASA's Curiosity rover has been tasked with investigating whether Mars had a habitable environment in its past, and two discoveries announced Tuesday are increasing that likelihood.

For years now, spacecraft orbiting the planet Mars have been detecting methane - an organic greenhouse gas, composed of atoms of carbon and hydrogen (CH₄), that can be produced by both geochemical and biological processes. Some of the first measurements taken by NASA's Curiosity rover appeared to rule out the observations from space, as researchers working with the data it provided saw no methane detections in Gale Crater.

However, over the past 20 months, the rover has taken a dozen samples of the air in Gale Crater, and it has found a trace 'background' amount of methane, amounting to less than 0.7 parts per billion of Mars' atmosphere. However, while those low levels are present during most of the measurements, at four different points, in late 2013 and early 2014, methane levels spiked to over ten times that amount.

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"This temporary increase in methane - sharply up and then back down - tells us there must be some relatively localized source," Sushil Atreya, a member of the Curiosity rover science team, said in a NASA JPL press release. "There are many possible sources, biological or non-biological, such as interaction of water and rock."

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Organics, not just in the air, but in the rocks too

In another study of the Martian environment, Curiosity drilled into rocks of a formation called Cumberland, and when it returned a portion of the rock dust to its Sample Analysis at Mars (SAM) instrument, the result was the discovery of organic chemicals trapped in the rocks.

According to NASA:

While it's been some time since these samples were taken (Curiosity was at Cumberland in May and June of 2013), it's taken that long for the scientists to be sure that these organic molecules were indeed from Mars. Other sources could have been meteorite dust, comet material, or even the rover itself. However, careful study of Curiosity's data give the scientists a good indication that these aren't from some foreign source.

A further complication to figuring out exactly what they're dealing with is the highly-reactive perchlorate minerals that are found in Martian soil. It's these same minerals that confounded measurements taken by the Viking lander, which was also looking for organic molecules in the soil back when it landed in June of 1976. After initially getting at least one promising result from a soil sample test (looking for organics and life), Viking heated the soil, which released perchlorates. This not only altered the composition of the organic molecules in the sample, but it would likely have killed anything that might have been alive in there as well. Curiosity is dealing with the same perchlorate problem with its samples, so exactly which organic molecules its dealing with are still unknown.

"This first confirmation of organic carbon in a rock on Mars holds much promise," said Roger Summons a participating scientist on the Curiosity team from MIT, according to the NASA JPL press release. "Organics are important because they can tell us about the chemical pathways by which they were formed and preserved. In turn, this is informative about Earth-Mars differences and whether or not particular environments represented by Gale Crater sedimentary rocks were more or less favorable for accumulation of organic materials. The challenge now is to find other rocks on Mount Sharp that might have different and more extensive inventories of organic compounds."

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A Taste of Martian Water

One other 'chemical' released from the rocks during Curiosity's investigation of this sample was H₂O, or water. There's nothing new about there being water on Mars, of course. They've been finding evidence of water ice for years now and Curiosity's investigations keep increasing the accepted amount of water on Mars' surface in the past. However, examining the specific properties of this water yielded some interesting results.

All water, whether it's on Earth, on Mars or other planets, or locked away in asteroids or comets, contains a certain number of molecules that are heavier than normal. Rather than being H₂O, these have one or both hydrogen atoms replaced by 'heavy hydrogen' or deuterium. Counting the number of hydrogen atoms vs the number of deuterium atoms in the water can tell you a lot about that particular water, including building a timeline of exactly when that water was trapped away in rocks. In this case, if Mars' original water had the same deuterium-to-hydrogen ratio that Earth started out with, the water trapped in the Cumberland rocks was found to have roughly three times that ratio, but only half of what the tiny amount of water vapour in Mars' atmosphere has today. This reveals that the rocks at Cumberland were laid down (and thus the water trapped inside their crystal structure) sometime after the planet lost its original water supply, but before it lost the majority of its subsequent water.

While NASA's MAVEN mission arrived at Mars back in October, to study how the planet lost most of its atmosphere, these latest measurements by Curiosity are helping with that mystery too.

"It's really interesting that our measurements from Curiosity of gases extracted from ancient rocks can tell us about loss of water from Mars," said Paul Mahaffy, the principal investigator of Curiosity's SAM instrument, and lead author of a report in the journal Science, detailing the rover's latest discovery.