Investigations on the Interplanetary Transfer of Microorganisms

PPARC使命对生物体从一个星球转移到另一个星球的两种可能方式：自然的（在岩石上和岩石中）和人工的（在航天器上）都非常感兴趣。首先，了解微生物在太空实验中的生存情况使我们能够第一次从经验上检验开尔文勋爵关于岩石上的生命从一个星球转移到另一个星球的开创性想法。在第二种情况下，样本返回或出站航天器的污染对PPARC参与Aurora、Rosetta和其他空间飞行任务至关重要。我们最近的工作表明，重要的基础科学问题可以在这些调查过程中得到解决。我们在这里提出的工作将继续我们的调查，旨在了解什么分散过滤器（障碍）作用于微生物从一个星球到另一个星球的转移。我们将采取四个欧空局空间实验-石头-模拟陨石坠落和这一过程对微生物的影响，BIOPAN -一个16天的空间暴露实验，和EXPOSE -两个1年的空间暴露实验。我们建议进行的实验主要集中在光合生物上，原因有几个：1）为了活跃，光合生物必须靠近岩石表面，从阳光中收集能量。这种习性通常表现为石内生长（在岩石表面下生长的生物体的离散层）。这使得它们在进入大气层时受到消融，因此使用它们可以深入了解在转移过程中对不同代谢组起作用的各种选择压力（“分散过滤器”），2）其中许多细胞具有静息状态，这将允许一些细胞在代谢不活跃状态下在岩石中更深处存活。这些实验帮助我们了解这些生物如何在转移中生存下来，它们可以作为所有其他类型的生活在岩石深处的生物的替代品，3）光合作用是最具生产力的新陈代谢形式，产生了我们今天在地球上看到的生命的多样性。了解这种在行星之间转移的代谢模式的潜力是天体生物学的兴趣，因为它将产生对星星承载多个生产性生物圈的能力的见解。一个潜在的批评是，光合生物不会被期望在航天器上。然而，这些生物体可用作模型系统，以了解空间条件对任何细胞材料和生物分子命运的影响。我们的工作将引起天文学家、行星科学家和生物学家的兴趣。

Both of the potential ways in which organisms could be transferred from one planet to another; natural (on and in rocks) and artificial (on spacecraft) are of great interest to the PPARC mission. In the first instance, understanding the survival of microorganisms in space experiments allows us, for the first time, to empirically test Lord Kelvin's pioneering ideas on the transfer of life on rocks from one planet to another. In the second case, contamination of sample return or outbound spacecraft is of crucial interest to PPARC's involvement in Aurora, Rosetta and other space missions. Our recent work has shown that important fundamental science questions can be addressed during the course of these investigations. The work we propose here will continue our investigations aimed at understanding what dispersal filters (barriers) act on the transfer of microorganisms from one planet to another. We will take advanatge of four ESA space experiments - STONE - to simulate meteoritic infall and the effects of this process on microorganisms, BIOPAN - a 16 day space exposure experiment, and EXPOSE - two 1 year space exposure experiments. The experiments we propose to undertake focus on photosynthetic organisms for several reasons: 1) To be active, photosynthetic organisms must be near the surface of a rock to gather energy from sunlight. Frequently this habit is manifest as endolithic growth (discreet layers of organisms growing just under the rock surface). This makes them subject to ablation during atmospheric entry and thus using them yields insights into the various selection pressures ('dispersal filters') that act against different metabolic groups during transfer, 2) many of them have resting states that would allow some cells to survive buried deeper in the rock in a metabolically inactive state. These experiments help us to understand how these organisms might survive transfer and they can be used as a proxy for all other types of organisms that live buried deep in rocks, and 3) photosynthesis is the most productive form of metabolism, yielding the great diversity of life we see on Earth today. Uderstanding the potential of this mode of metabolism to be transferred between planets is of astrobiological interest because it would yield insights in to the ability of a star to host multiple productive biospheres. One potential criticism is that photosynthetic organisms would not be expected on spacecraft. However, these organisms can be used as model systems to understand the effects of space conditions on any cellular materials and the fate of biomolecules. Our work will be of interest to astronomers, planetary scientists and also biologists.