My UK Space Agency Aurora Fellowship was to study the effects of the cosmic radiation on Mars on our ability to detect signs of past martian life using Raman spectroscopy aboard the ExoMars rover. The full description of this fellowship proposal is as follows:


Is the Earth the only world in our solar system to harbour life?

This is one of the most fundamental questions asked throughout human history, and one that we are now becoming technologically capable of answering. Astrobiology is the field of science engaged with understanding the limits of life on Earth, and where else the conditions for biology might be met. Mars is believed to have provided the fundamental requirements for the emergence and maintenance of life, at least early in its history. Different lines of evidence, called biosignatures, for extinct, or perhaps even extant, hardy microorganisms may remain detectable in the martian surface. Raman spectroscopy is a promising technique for detecting biosignatures of hidden life and has been selected for the ExoMars-C rover mission, due for launch in 2018.

The martian surface today, however, is hostile to the survival of microorganisms and the preservation of organic biosignatures. A major hazard in the top metres of the martian ground is the penetration of high-energy ionising radiation particles – the cosmic rays. Unlike the Earth, Mars doesn’t receive any significant shielding against this destructive radiation from its thin atmosphere and lack of magnetic field. This irradiation over long timescales will sterilise populations of microbial life and also degrade the complex organic molecules that would remain as biosignatures of their prior existence. ExoMars will also have a drill and so importantly will be able to recover martian soil form a depth of up to 2m underground, where it would have received some protection from the cosmic radiation and harsh surface conditions.

The important questions that need to be answered, therefore, are:
1. How fast do the distinctive peaks of the Raman spectroscopic ‘fingerprint’ of different biosignature compounds decrease with exposure to radiation – i.e. what is the window of opportunity for detecting the biosignatures before they are erased, and so what might be the minimum drilling depth for successful detection?
2. How are the Raman spectroscopic fingerprints of different biosignatures distorted or modified as the compounds break-down under the radiation – i.e., which Raman biosignatures are the most reliable and will remain unambiguously recognisable?

I want to answer these questions by using Raman spectroscopy to study pure biosignature compounds and samples of Earthly microorganisms colonising extreme habitats after exposing them to increasing doses of gamma-rays. This will allow me to characterise how the Raman fingerprints of different biosignatures might change, and how quickly they are erased with radiation. I have already used computer models to calculate the radiation environment on the martian surface and at different depths underground. So using my modeling results I can link the total radiation doses used in these new experiments to the length of time that corresponds to in the cosmic radiation on the martian surface and at different depths underground.

By the end of this project, I’ll understand both the manner and the rate of biosignature degradation by ionising radiation, and how deep might be sufficient to expect persisting signs of life with the Raman spectrometer. This understanding will be crucial for the proper interpretation of Raman spectra taken by ExoMars and ensuring the success of this exciting space mission.

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