Planetary protection is governed by the Outer Space Treaty and includes the practice of protecting planetary bodies from contamination by Earth life. Although studies are constantly expanding our knowledge about life in extreme environments, it is still unclear what the probability is for terrestrial organisms to survive and grow on Mars. Having this knowledge is paramount to addressing whether microorganisms transported from Earth could negatively impact future space exploration. The objectives of this study were to identify cultivable microorganisms collected from the surface of the Mars Science Laboratory, to distinguish which of the cultivable microorganisms can utilize energy sources potentially available on Mars, and to determine the survival of the cultivable microorganisms upon exposure to physiological stresses present on the martian surface. Approximately 66% (237) of the 358 microorganisms identified are related to members of the Bacillus genus, although surprisingly, 22% of all isolates belong to non-spore-forming genera. A small number could grow by reduction of potential growth substrates found on Mars, such as perchlorate and sulfate, and many were resistant to desiccation and ultraviolet radiation (UVC). While most isolates either grew in media containing ‡10% NaCl or at 4°C, many grew when multiple physiological stresses were applied. The study yields details about the microorganisms that inhabit the surfaces of spacecraft after microbial reduction measures, information that will help gauge whether microorganisms from Earth pose a forward contamination risk that could impact future planetary protection policy.
We use the Hoshen–Kopelman algorithm with the Nakanashi method of recycling redundant labels to measure the fraction of spanning configurations, R(pc), at and near pc, for random site percolation in two and three dimensions with different boundary conditions. For the square and cubic lattices we find that R(pc) is 0.50 and 0.28 for free edges and 0.64 (2-d) and 0.56 (3-d) for both helical and periodic boundary conditions. The error bars are of the order of ±0.01 for these results.
The result of equal parts serendipity, exploration, creativity, and the enduring persistence of a dedicated team of designers and its university client, Washington University's Living Learning Center, has quickly become a locus of sustainability. It is a deep green place filled with fresh air and daylight, an ongoing achievement in zero net waste, zero net water, and zero net energy design, a space that inspires higher learning about the natural world. The Center is also well on its way to certification as the first living building in the world.
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