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Mineral may destroy organics that Curiosity is seeking

Paul Sutherland, Feature writer
Feb 21, 2015, 17:50 UTC

Sen—A NASA robotic rover on Mars may be inadvertently destroying the very signs of life it is searching for by cooking it, scientists have warned.

The Curiosity rover, which landed in August 2013, is exploring an old lake bed in Gale Crater on the Red Planet, to find out if it has ever been inhabited by martian microbes.

In a key experiment, it blasts samples of martian soil with intense bursts of heat to break them down into the chemicals that they are made of, in a quest to find organic compounds. These are not evidence of life in themselves, they are its vital ingredients.

But a UK team of scientists warn that if a particular mineral is present, then both it and the organic material will be destroyed by this flash-heating technique. It means that Curiosity’s zapper could be destroying any evidence of aliens.

The discovery was made by researchers from Imperial College London and the Natural History Museum. They replicated an experiment called the Sample Analysis at Mars (SAM) instrument on Curiosity, otherwise known as Mars Science Laboratory, which looks for evidence of organic compounds by heating samples up to around 1,000° C to release gases.

These gases are then analysed to see if any organic material is present. However, the scientists found that an iron sulphate mineral called jarosite breaks them down if it is present, destroying them and itself.

Jarosite is one of several minerals for which NASA is searching as its presence could indicate that an environment was habitable in the past. But the team’s tests revealed that flash-heating breaks jarosite down into sulphur dioxide and oxygen, and that the oxygen then destroys the organic material, leaving no trace of it.

They fear that this may be happening on Mars if Curiosity is collecting samples of martian soil that have jarosite in them.

Co-author of the new study, published in the journal Astrobiology, was Professor Mark Sephton, from Imperial College’s Department of Earth Science and Engineering, who previously identified another mineral, perchlorate, that can cause similar problems in detecting organic compounds.

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The SAM experiment being fitted to Curiosity before its launch. Image credit: NASA

He said in a statement: “The destructive properties of some iron sulphates and perchlorate to organic matter may explain why current and previous missions have so far offered no conclusive evidence of organic matter preserved on Mars’ surface. This is despite the fact that scientists have known from previous studies that organic compounds have been delivered to Mars via comets, meteorites and interplanetary dust throughout its history.”

On Earth, iron sulphate minerals like jarosite form in acidic waters that flow from rocks rich in sulphur. Despite the harsh environment, these waters are home to certain bacteria, which makes these minerals of great interest to scientists studying Mars. The jarosite samples used in the experiments came from Brownsea Island in Dorset, England.

All is not lost if jarosite is found to be in the Mars samples. Professor Sephton believes that if organic material is broken down by the heating, then Curiosity’s SAM instrument could detect a sudden spike in the level of carbon dioxide present.

And despite the new concerns, Curiosity has already detected organic material in some of its samples, including a spike in methane from a drilled rock dubbed Cumberland in 2013. Members of the mission team point out that it does not rely on SAM alone to detect organics.