Concern for Mars mission as mineral destroys organic compounds

As NASA’s Curiosity mission searches for various minerals on Mars, in the hope of finding evidence of ancient habitable environments, British scientists have found that one such mineral (jarosite) breaks down organic compounds when it is flash-heated. Their research has been published in the journal Astrobiology.

On Earth, iron sulfate minerals like jarosite form in the acidic waters flowing out of sulfur-rich rocks. Despite the adverse conditions, these waters are a habitat for bacteria that use these dissolved sulfate ions. This makes the minerals of interest to scientists studying Mars, as their presence provides evidence that acidic liquid water was present at the same time the minerals formed - which could have provided an environment favourable for harbouring ancient microbial Martian life.

On board the rover Curiosity, the Sample Analysis at Mars (SAM) instrument analyses soil samples for evidence of organic compounds by progressively heating samples up to around 1000°C (flash heating), which releases gases. These gases can then be analysed by gas chromatography and mass spectrometry, which can identify molecules in the gas and see if any organic compounds are present.

Researchers from Imperial College London and the Natural History Museum replicated the technique with a combination of jarosite and organic compounds. The team discovered that the instrument’s technique broke down jarosite into sulfur dioxide and oxygen, with the oxygen then utterly destroying the organic compounds. They noted that if jarosite is present in soil samples that Curiosity analyses, researchers may not be able to detect it because both the jarosite and any organic compounds could be destroyed by the flash-heating process.

Study co-author Professor Mark Sephton, from the Department of Earth Science and Engineering at Imperial College London, last year found a similar issue with the mineral perchlorate. Flash-heating causes the mineral to break down and to give off oxygen and chlorine gas, which in turn react with any organic compounds, breaking them down into carbon dioxide and water.

“The destructive properties of some iron sulfates 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,” Professor Sephton said. “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.”

But Professor Sephton has shown that though the reaction of perchlorate was problematic, scientists could potentially use the spike in carbon dioxide resulting from the experiment to detect the presence of organic compounds in the sample being analysed. The team suggests a similar approach may alert scientists to the presence of jarosite.

The next step will see the researchers using synthetic jarosite in their experiments, which will enable a cleaner decomposition process to occur when the mineral is flash-heated. This will allow for more precise measurements to be taken when the oxygen is released and will hopefully enable such measurements to be taken from potential mineral samples on Mars.

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