Signs of Martian life could be lurking deep below planet surface

Signs of life may be present deep inside the surface of Mars, rather that in rocks excavated by some meteorite impacts, a new study suggests.

Scientists analysing samples from Mars' surface have so far not conclusively detected organic compounds that are indigenous to the red planet, which would be indicators of past or present life.

The inconclusive results mean that researchers are now suggesting that a good place to find these organic compounds would be deep underground from rocks that have been blasted to the surface by meteor impacts.

This is because such rocks have been sheltered from the Sun's harmful radiation and from chemical processes on the surface that would degrade organic remains.

Scientists from Imperial College London and the University of Edinburgh in the UK has replicated meteorite blasts in the lab 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 study suggests that rocks excavated through meteorite impacts may incorrectly suggest a lifeless early Mars, even if indicators of life were originally present.

The team replicated blast impacts of meteorites of around 10 metres 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.

However, 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 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.

"Rocks excavated through meteorite impacts provide scientists with another unique opportunity to explore for signs of life, without having to resort to complicated drilling missions," said Mark Sephton, Professor at Imperial College London.

"Our study is showing us is that we may need to be nuanced in our approach to the rocks we choose to analyse," said Sephton.

"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 Wren Montgomery, from Imperial College London.

The study was published in the journal Scientific Reports.