The Emergence of Habitable Conditions in the Solar System

太阳系是如何从原行星盘的暴力中脱颖而出，成为适合生命生存的环境的？尽管人们非常关注太阳系中目前天体的可居住性，但对于太阳系天体是如何随着时间的推移而进化的，以及导致潜在可居住的水环境的起始条件是什么，人们的理解却非常少。如果我们了解了导致太阳系走向或远离宜居条件的因素，我们才能真正评估宇宙中是否存在宜居条件（STFC科学优先事项的一个关键目标）。这是我们在这里提出的工作的基本目标。一个主要的挑战是了解早期太阳系的挥发物清单，以及早期太阳系天体中有哪些挥发物可能导致可居住的水环境。为了解决这个问题，我们需要更好地掌握早期太阳系物质的组成。彗星是这类天体中非常重要的一类。在这项工作中，我们将大大提高我们对彗星的分类和组成的理解。虽然彗星不是早期太阳系中挥发物的唯一提供者，但它们提供了对太阳系构成物质的关键见解，并定义了早期挥发物和潜在流体的边界条件。一旦这些挥发物合并成行星体，它们就形成了我们今天在太阳系中观察到的许多水环境（早期的火星、木卫二、土卫二，甚至像谷神星这样的小行星）。然而，这些水环境是如何演变的。当早期挥发物的溶液冻结时会发生什么？结果是什么？关键的挥发物，如降低冰点的氨，是如何改变这些溶液的？最关键的是，在这些不断进化的液体中，宜居性是如何改变的？我们将通过将行星科学与天体生物学（微生物学）联系起来来解决这些问题，以调查和推进我们对早期太阳系解决方案的可居住性如何随着时间的推移而演变的理解。就行星宜居性而言，房间里一个看不见的大象是重力。它在所有环境中无处不在，即使它的影响是由于它几乎不存在造成的。在国际空间站的生物小行星实验中，我们将利用我们的太空飞行实验传统，利用我们为太空飞行开发的设备，研究生物在原始小行星物质（球粒物质）上的生长。与我们之前使用玄武岩进行的biorrock实验中收集的数据进行比较，将使我们能够研究早期太阳系天体和材料的生长和可居住性，特别是在低重力条件下的球粒状太阳系小型天体的可居住性。这项工作将为我们提供重要的新见解，让我们了解引力在定义太阳系天体的可居住性方面的作用。STFC的首要任务是找出地球上是否只有生命，但为了最终在可居住的环境中寻找生命，我们必须能够将其与非生命区分开。众所周知，化学过程会产生伪生物特征——看起来像生命的形态和化学特征。然而，我们对早期的太阳系环境，如冰冷的卫星和早期的火星，是如何产生生命的错误信号知之甚少。如果我们要避免被误认为我们已经发现了生命，那么了解早期太阳系是如何产生类生命物质的特征是至关重要的。我们将大大提高我们对早期太阳系产生这种伪生物特征的能力的理解。总之，我们提出的项目是一个连贯而系统的研究项目，旨在了解早期太阳系是如何演变成适宜居住的环境的，以及我们如何在适宜居住的行星环境中可靠地寻找生命的迹象。

How do solar systems emerge from the violence of the protoplanetary disc to be habitable environments for life? Although there is much focus on the present-day habitability of bodies in our Solar System, there is remarkably little understanding of how Solar System bodies have evolved over time and what the starting conditions were that led to potentially habitable aqueous environments. We can only really assess whether habitable conditions might be common in the Universe (one key objective of STFC's science priorities) if we understand the factors that canalise a Solar System towards or away from habitable conditions. This is the fundamental aim of the work we propose here.One major challenge is understanding the volatile inventory of the early Solar System and what volatiles were available in early Solar System bodies that could have led to habitable aqueous environments. To address this problem we need to have a better grasp of the composition of early Solar System materials. One enormously important class of such bodies is comets. In this work, we will significantly advance our understanding of the taxonomy and composition of comets. Although comets are not the only providers of volatiles in the early Solar System, they provide key insights into the materials from which solar systems are made and that define the boundary conditions for early volatiles and potential fluids. Once these volatiles coalesced into planetary bodies, they led to the many aqueous environments we observe in the Solar System today (early Mars, Europa, Enceladus, even asteroids such as Ceres). However, how have these aqueous environments evolved. What happens when solutions of early volatiles freeze and what solutions result? How do key volatiles, such as ammonia, which depress the freezing point, alter these solutions? Most crucially, how does habitability alter in these evolving fluids? We will address these questions by linking planetary sciences with astrobiology (microbiology) to investigate and advance our understanding of how the habitability of early Solar System solutions have evolved over time.An unseen elephant in the room in terms of planetary habitability is gravity. It is pervasive in all environments, even if its influence is caused by its near absence. Using our heritage of flying space experiments, we will use equipment we have developed for spaceflight to study the growth of organisms on primitive asteroidal material (chondritic material) in the BioAsteroid experiment on the International Space Station. Comparisons with data gathered in our previous BioRock experiment using basalt will allow us to investigate the growth and habitability of early Solar System bodies and materials and, in particular, the habitability of chondritic small Solar System bodies under low gravity regimes. This work will give us important new insights into the role of gravity in defining the habitability of solar system bodies.STFC has a scientific priority to find out if life is unique to Earth, but to eventually look for life in habitable environments, we have to be able to distinguish it from non-life. Chemical processes are known to generate pseudo-biosignatures - morphologies and chemical signatures that look like life. Yet we know very little about how early Solar System environments, such as in icy moons and early Mars, might have generated false signatures of life. Understanding how early solar systems might generate signatures of life-like materials is essential if we are to avoid being misled into thinking we have found life. We will significantly advance our understanding of the ability of the early Solar System to produce such pseudo-biosignatures.In summary, our proposed projects fit together into a coherent and systematic programme of study to understand how the early Solar System evolved into habitable conditions and how we might reliably seek signatures of life within habitable planetary environments.