S.A.M. (the Sample Analysis at Mars)
A mineral was identified which, when heated, destroys organic compounds. The discovery, published in Astrobiology, could have consequences for the NASA’s rover, Curiosity for future missions, like ExoMars, dedicated to the search for traces of life on the Red Planet.
The culprit is called SAM. It had been sent to Mars to hunt for signs of past life. Until now the loot was a bit disappointing.
Credit: NASA GSFC
SAM is the Sample Analysis at Mars: the greatest among the instruments on board the NASA’s rover, Curiosity. To reconstruct what happened, it is necessary first to know how, the sophisticated chemical laboratory on wheels, to study the samples collected and to identify the substances they contain. In short, they overheat. When they reach temperatures of around one thousand degrees, the samples liberate gas that can be analyzed in situ with gas chromatography and mass spectrometry, techniques widely proven able to recognize the molecules present in the gas and, in particular, to realize if among these are present also of organic compounds.
And that’s where it comes in, the sleek jarosite, a mineral of the family of ferric sulfates. Here on Earth, minerals such as jarosite, we meet mostly in hostile environments, typically in acidic water leaking from rocks rich in sulfur. Hostile environments for us but ideal for certain bacteria that feed the ions dissolved in the sulfuric waters. This characteristic makes the jarosite a valuable witness for scientists looking for traces of extraterrestrial life: where it meets jarosite, say, once there had to be acidic water, water that could offer a favorable environment to accommodate ancient forms of microbial life.
Well, the jarosite on Mars is not lacking. In some ways there is also too much, as it was discovered to its cost one of the predecessors of Curiosity, the little robot Spirit, who in May 2009 was just covered up in a patch of soft powder ferric sulfate. A powder with a seal so low that the wheels were never been able to pull out the rover.
In short, that the jarosite could be an ugly beast, it already had been experienced. Instead, what it was not put into account is that, when heated by SAM, the jarosite releases sulfur dioxide and oxygen. And the oxygen, wrote researchers at Imperial College London on Astrobiology, destroys any organic compounds present in the sample without a trace.
A “perfect crime” that could clarify one of the most daunting of Martians puzzles. “The destructive properties of some iron sulfates, such as perchlorate, towards organic compounds may explain why current and past missions are not up to now failed to provide conclusive evidence of the presence of organic matter on the soil of Mars,” observes Mark Sephton, one of the authors of the study. “And this despite the fact that scientists know from previous studies that organic compounds on Mars were deposited along the entire course of its history: from comets, meteorites and interplanetary dust.”
Fortunately, all is not lost. A trace, in fact, could remain, the article suggests: if the sensors of SAM, during the analysis of a sample containing jarosite, were to detect an abnormal spike in the level of carbon dioxide, this could mean that a process of destruction of organic compounds is in progress. An indirect indication of which we can take into account both for the next steps of Curiosity and the prospective hunters Martian life, first of all ExoMars.