Investigations on the Interplanetary Transfer of Microorganisms

生物体可以从一个星球转移到另一个星球的两种潜在方式：自然的(在岩石上和在岩石上)和人造的(在航天器上)都是PPARC任务非常感兴趣的。首先，了解微生物在太空实验中的生存情况，使我们第一次能够从经验上检验开尔文勋爵关于将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。在第二个案例中，样品返回或出站航天器的污染对PPARC参与极光、罗塞塔和其他空间飞行任务至关重要。我们最近的工作表明，在这些调查过程中，重要的基础科学问题可以得到解决。我们在这里提出的工作将继续我们的调查，旨在了解扩散过滤器(屏障)在微生物从一个星球转移到另一个星球上所起的作用。我们将利用欧空局的四个空间实验--STONE--模拟陨石坠落及其对微生物的影响，BIOPAN--一个16天的空间暴露实验，以及--两个为期一年的空间暴露实验。我们建议进行的实验主要集中在光合作用生物上，原因有几个：1)光合作用生物必须靠近岩石表面才能从阳光中收集能量，才能发挥作用。这种习性通常表现为石器时代内的生长(就在岩石表面下生长的分散的有机体层)。这使得它们在进入大气时容易被烧蚀，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(“扩散过滤器”)；2)它们中的许多具有休眠状态，允许一些细胞在新陈代谢不活跃的状态下在岩石深处存活。这些实验帮助我们了解这些生物是如何在转移中存活下来的，它们可以作为生活在岩石深处的所有其他类型生物的替代品，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巨大多样性。了解这种新陈代谢模式在行星之间转移的可能性具有天体生物学意义，因为它将产生对恒星拥有多个生产性生物圈的能力的洞察。一个潜在的批评是，宇宙飞船上不会有光合作用的有机体。然而，这些生物可以作为模型系统来理解空间条件对任何细胞材料的影响和生物分子的命运。天文学家、行星科学家和生物学家都会对我们的工作感兴趣。

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.