Determining Favorable Environments for Endolithic Growth From Physics Considerations Doug Archer, Dr. David Allred Dept. of Physics and Astronomy Brigham Young University

What’s an Extremophile? Extremophile’s are organisms that can live in extreme environments Examples are Halophiles, Thermophiles, and Endoliths

Limits on Life Lack of Liquid Water Temperature extremes Ultraviolet Radiation Soil toxicity Sparse Energy Resources

Mars Had Water in the Past and Still Has Water Today

Temperature Concerns Mars’ Temperature range -123C to 20C Once thought a major concern, the discovery of Extremophiles metabolically active from -15C to 120C has changed our thinking. Active->Dormant cycle

Ultraviolet Radiation UVA = 400-315nm UVB = 315-280nm UVC = 280-200nm Below ~290nm, UV energy is very damaging to most biological systems. It affects proteins, lipids, and most importantly, DNA.

UV Flux, Earth vs. Mars UVC and B (W/m^2) UVA DNA effective irradiance Present Day Earth 1.86 52.81 .1 Present Day Mars 13.2 41.5 116.4 Early Earth 5.2 34.1 41 Early Mars 4.8 22.3 33.8

The Role of Ozone The Chapman Reaction describes ozone creation/reaction. Ozone absorbs between 200-360nm Mars’ ozone layer is <1% of earths at maximum

UV Damage

Surviving UV There are three primary methods: Avoidance: chemoautotrophs Repair: photolyase cuts thymine dimers. Present in modern branches of ancient archaebacteria. Protection: Matting, Substrate Production, Physical Environment Sheltering.

Why Endoliths? Endolithic communities, also known as cryptoendoliths, could provide protection from numerous life limiting conditions. We have ready access to endoliths in the Southern Utah Desert.

Physics Concerns Which compounds found in common minerals block UV? This is a function of band gap Is UV light preferentially absorbed or scattered out of certain materials? Rayleigh vs. Mie scattering Particle size (<1/10 wavelength=Ray.) Wavelength Dependence (λ^4 vs λ) How fast does the intensity drop as a function of depth and wavelength To what extent is color important and how is it produced?

Martian Minerology Sample Na2O MgO Al2O3 SiO2 SiO3 K2O CaO TiO2 Fe2O3 Near Yogi 3.7 8.1 8.9 46.8 6.3 0.2 5.5 1.4 15.6 Scooby Doo 1.9 6.9 50.3 5.2 0.5 7.1 1.1 14.5 Rocky Flates:crust  -- 7.4 7.2 44.1 10 0.9 5.9 0.6 18.3

Absorption Example

Correlate and Compare Minerals with Fe203: Hematite, Maghemite Compare to Martian minerals using spectography and terrestrial analogues. USGS Imaging Spectroscopy Have found abundant Olivene (Mg1.6Fe2+0.4(SiO4))

Remaining Questions Can microporosity and capillary action act to prevent or lessen dessication of the cryptoendoliths? How can we robotically detect the presence of Endoliths?

Conclusions Given what we know about the early history of Earth and Mars, it is not a stretch to theorize that life appeared simultaneously. Earth provided a more successful habitat, but conditions on Mars do not preclude the continued presence of life. Endolithic habitats provide a refuge from many of the limiting factors on life as we know it.