Is there life on Mars? Meteorites may be destroying the evidence

As the search to find signs of life on Mars continues, researchers have suggested that a good place to find organic compounds native to the planet would be deep underground — from rocks that have been blasted to the surface by meteorite impacts. The theory goes that such rocks have been sheltered from the sun’s harmful radiation and from chemical processes on the surface that would degrade organic remains. But is this really the case?

Scientists from Imperial College London and the University of Edinburgh have now replicated meteorite blasts in the lab in order to see if organic compounds encased in rock could survive the extreme conditions associated with them being blasted to the surface of Mars by meteorites. The team carried out their research by subjecting different types of organic matter to extreme pressure and temperature in a piston cylinder device. They then did a chemical analysis using pyrolysis-gas chromatography mass spectrometry.

Replicating blast impacts of meteorites of around 10 m in size, the researchers found that the types of organic compounds found in microbial and algal life — long chain hydrocarbon-dominated matter — were destroyed by the pressures of impact. Meanwhile, the types of organic compounds found in plant matter — dominated by aromatic hydrocarbons — underwent some chemical changes, but remained relatively resistant to impact pressures. Meteorites often contain organic matter not created by life, which have some similarities in their organic chemistry to land plants. The team infer that they also should also be resistant to blast impacts.

The study, published in the journal Scientific Reports, therefore suggests that rocks excavated through meteorite impacts may incorrectly suggest a lifeless early Mars, even if indicators of life were originally present. The good news is that this could help future missions to Mars determine the best locations and types of blast excavated rocks to examine to find signs of life. For example, it may be that meteorite impacts of a certain size may not destroy organic compounds or scientists may need to concentrate on rocks excavated from a certain depth.

“The study is helping us to see that when organic matter is observed on Mars, no matter where, it must be considered whether the sample could have been affected by the pressures associated with blast impacts,” said Dr Wren Montgomery, a co-author on the study from Imperial College London. “We still need to do more work to understand what factors may play an important role in protecting organic compounds from these blast impacts. However, we think some of the factors may include the depths at which the rock records are buried and the angles at which meteorites hit the Martian surface.”

The next steps will see the team investigating a broader range of pressures and temperatures, which would help them understand the likely effects of a greater range of meteorite impacts. This would enable them to identify the specific conditions under which organic material may escape the destructive effects of blasts — even when excavated from deep underground by violent events. This could help future Mars missions further refine the types and locations of rocks that they can analyse for signs of past or present life.

This is a modified version of a news item published by Imperial College London under an Attribution-NonCommercial-ShareAlike Creative Commons licence (CC BY-NC-SA 4.0). This version is similarly licensed under CC BY-NC-SA 4.0

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