Interplanetary transfer of photosynthesis: an experimental demonstration of a selective dispersal filter in planetary island biogeography.

We launched a cryptoendolithic habitat, made of a gneissic impactite inoculated with Chroococcidiopsis sp., into Earth orbit. After orbiting the Earth for 16 days, the rock entered the Earth's atmosphere and was recovered in Kazakhstan. The heat of entry ablated and heated the rock to a temperature well above the upper temperature limit for life to below the depth at which light levels are insufficient for photosynthetic organisms ( approximately 5 mm), thus killing all of its photosynthetic inhabitants. This experiment shows that atmospheric transit acts as a strong biogeographical dispersal filter to the interplanetary transfer of photosynthesis. Following atmospheric entry we found that a transparent, glassy fusion crust had formed on the outside of the rock. Re-inoculated Chroococcidiopsis grew preferentially under the fusion crust in the relatively unaltered gneiss beneath. Organisms under the fusion grew approximately twice as fast as the organisms on the control rock. Thus, the biologically destructive effects of atmospheric transit can generate entirely novel and improved endolithic habitats for organisms on the destination planetary body that survive the dispersal filter. The experiment advances our understanding of how island biogeography works on the interplanetary scale.

The microbiology of spacecraft hardware: lessons learned from the planetary protection activities on the Beagle 2 spacecraft.

We consider the aseptic assembly of the Beagle 2 Mars probe and how the requirements of COSPAR planetary protection category IVa were achieved. Several areas for future investigation became apparent. An ESA mission is outlined in which a microbial bioburden is recovered after Earth orbit to assess viability following re-entry through the atmosphere.

Atmospheric entry simulations of Mars lander bioload--experiments in support of Beagle 2.

Simulations of the temperature and vacuum effects of Martian atmospheric entry upon Bacillus atrophaeus (formerly Bacillus subtilis var niger; 8058; NCIMB) endospores were carried out inside a purpose-built vacuum chamber. The work formed part of the study in support of planetary protection for the Beagle 2 Mars lander and investigated to what extent the outer surface of the lander's back heat shield would be sterilised during Mars atmospheric entry. The spores were heated to peak temperatures up to 300 degrees C over 30 s under vacuum conditions (10(-3) mbar). There was no effect on spore viability until peak temperatures reached 180-200 degrees C (12-15 s of heat exposure). Spore viability then fell rapidly with increasing temperature. Once peak temperatures exceeded 300 degrees C, no further spore viability was detected. The average heating rate was rapid (10 degrees C s(-1)); thus spores were exposed to peak temperatures for less than a second. These data inform on the process of determining bioburden reduction and control steps necessary for external surfaces of spacecraft which are non-sterile at launch, as well as providing new information about the ability of a model resistant organism to survive rapid, short-duration heating.