Lifeless Martian Samples and Their Significance

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Although a major objective in Mars exploration is the search for life, there are many scenarios that could lead to the recovery of lifeless samples. What could lifeless samples tell us about Mars and its habitability?

Mars is today a cold desert world whose surface is thought to be largely uninhabitable1. However, the planet hosts abundant evidence for a more hydrologically active past2,3 particularly in the Noachian (circa 4.1 to 3.7 billion years ago). These observations raise the question of how widespread habitable environments were and whether they hosted life.
Investigations of Gale Crater by the NASA Mars Science Laboratory (MSL) suggest that Martian lakes of moderate pH and salinity were redox-stratified and contained iron and sulfur in multiple oxidation states with the potential to yield energy for microbial metabolism ~3.7 billions of years ago4,5. Habitable conditions have also been suggested for the Phoenix landing site in Vastitas Borealis in the north polar region of Mars during past obliquity variations6. These findings support the hypothesis that Mars hosted conditions favourable for life and have revived interest in missions focused on the detection of preserved biosignatures7. The possibility of stable liquid water in surface and subsurface environments continues to motivate speculation about whether the planet hosts habitable conditions at the present-day8,9.
Although approaches to finding evidence of life in Martian samples have been discussed extensively, little consideration has been given to the significance of recovering lifeless samples, i.e. samples devoid of any discernible trace of past or present biological activity. Lifeless samples would provide significant insights into the habitability and biological trajectory of Mars. We discuss scenarios that might lead to lifeless samples, how those scenarios could be tested, and what research directions they motivate.
Original languageEnglish
JournalNature Astronomy
Publication statusPublished - 3 Jun 2019


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