Natural Transfer of Viable Microbes in Space 1. From Mars to Earth and Earth to Mars

Planetary targets in the search for extrasolar oxygenic photosynthesis

“…Gladman (1997) suggested that 10 to 20% of the radius of small meteorites is destroyed. In computer calculations, Mileikowsky et al (2000) showed that a rock requires a diameter of more than 0.2 m to avoid being heated to above 100 °C throughout.…”

“…Mileikowsky et al (2000) calculated that behind 1 m of shielding Bacillus subtilis spores could survive for about a million years, with this survival period dropping to 300,000 years behind 10 cm of shielding caused by secondary radiation effects in the rock. Clark similarly finds that within a million years a meteorite would be sterilised to 1 m depth and that the top 3 cm of a rock, i.e.…”

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

“…The SNC meteorites from Mars have mineral assemblages that also suggest high-pressure magmatic processes (Frankel, 1996), implying that radioelements are similarly concentrated at shallower levels. Uranium and thorium contents in Martian meteorites are lower than in Earth crust samples (Mileikowsky et al, 2000), but the meteorites do not represent the rock types in which radioactive minerals become concentrated: a random sampling of twenty rocks from the Earth's crust would probably also show no evidence for uranium or thorium concentration. Gamma-ray spectrometry data from Phobos 2 (McLennan, 2001) and Mars Odyssey (Taylor et al, 2003) indicate higher levels in Martian soils than recorded in the meteorites, but still at lower concentrations than on Earth.…”

Ionizing Radiation and Life

“…More specifically in the interests of astrobiology, several modeling studies have involved calculation of the radiation dose profile generated by CR through the martian regolith to predict the likely survival times of spore-forming or radiation-resistant bacterial strains such as D. radiodurans in the subsurface (Mileikowsky et al, 2000;Pavlov et al, 2002;Kminek et al, 2003;Dartnell et al, 2007aDartnell et al, , 2007bDartnell et al, , 2010. While there are uncertainties in both the physics of high-energy particle transport and the biological response to irradiation, these studies broadly agree and have found that the top 20 cm of the martian surface is sterilized of even the most radiation-resistant microorganisms (based on terrestrial models such as D. radiodurans) within a million years or so, with greater survival found at increasing depths due to shielding, especially in ice deposits (Dartnell et al, 2007a).…”

“…While there are uncertainties in both the physics of high-energy particle transport and the biological response to irradiation, these studies broadly agree and have found that the top 20 cm of the martian surface is sterilized of even the most radiation-resistant microorganisms (based on terrestrial models such as D. radiodurans) within a million years or so, with greater survival found at increasing depths due to shielding, especially in ice deposits (Dartnell et al, 2007a). In material with a density of around 1 g/cm 3 , the more energetic GCR cascades begin to dominate over the average SEP flux within around 10 cm depth (Dartnell et al, 2007a), and radiation from the GCR cascades peaks at (the Pfotzer maximum) 25-50 cm deep and at a third of that depth within solid rock or regolith (Mileikowsky et al, 2000;Pavlov et al, 2002;Dartnell et al, 2007b). Beneath the penetration of GCR cascades, at 3-4 m depth, depending on surface properties, the remaining source of ionizing radiation is the decay of radionuclides in the surrounding regolith.…”