Title pageLife on Mars?Using Geant4 to model the subsurface

radiation environment

Lewis DartnellCoMPLEX (Centre for Mathematics and Physics in the

Life Sciences and Experimental Biology)

University College London, UK

Supervisors: Andrew Coates, MSSL John Ward, Biochemistry

SPENVIS-GEANT4 workshop. Leuven, 3-7 October 2005

Summary

• Refugial life on Mars?• My research & computer model

Why Mars?

• Most Earth-like body in the solar system• Known to have once been warm and

wet, with a thick atmosphere andmagnetic field

• The original home of life?

Mars today• 6 mbar atmosphere, freezing surface temperatures, bone-dry

surface sterilised by UV, bathed in solar energetic and cosmicradiation particles

Refugial Life

• Could extremophile life persist beneaththe surface, within pockets of liquidwater…?

• Deep hot Biosphere on Earth.• Methane plumes detected seeping out of

ground.

ExtremophilesMicrobes on Earth survive extremes of:

Temperature:113ºC superheated water --> -18ºC ice pockets

pH:pH 0 sulphuric acid --> pH 11 soda lakes

Salinity:saturated brine --> pure distilled water

Pressure:1,000 atm --> vacuum

As well as entire ecosystems independentof energy from the sun - 5km deep ‘rock-eaters’ and hydrothermal ventcommunities

Space radiation

Radioresistant bacteria

Survival curves of D. radiodurans, B. subtilis, and E. coliDeinococcus radiodurans

The Model

Crustal Anomalies

• Failure of global magnetic field ~4Gya, withsubsequent loss of atmosphere and environmentalcollapse.

• Remnant magnetism stored in rocks. Effect onincoming radiation?

Final Goal

• Which sitesshould we sendour landers to?

• How deep wouldthey need to drill?