Analytical Chemistry in Astrobiology

Astrobiology as a field of science aims to answer three fundamental, yet complex questions humans have been asking in various forms for generations: “Does life exist elsewhere in the universe? How did life begin and evolve? What is life’s future on Earth and beyond?” For nearly all of human history, these questions were in the realm of philosophy and science fiction. Now, with significant advancements in science and technology and the ability to enter space, we can finally begin answering these questions through scientific investigations. At-tempting to understand the origins and distribution of life in the universe requires a general understanding of the nature of life, but arriving at a working definition for life has historically proven difficult, due in part to the fact that we have a sample size of one. The NASA Astrobiology Institute has defined life as: “A self-sustaining chemical system capable of Darwinian evolution”.1 While this definition serves as a provisional guide in our search for extraterrestrial life and the study of terrestrial life’s origin, the exact nature of life on other worlds may vary significantly from what we observe on Earth due to the different chemical inventories and selective pressures present in these environments. Thus, when searching for life, it is important that we not only search for life as we know it, but also for life as we do not. Determining the origin of life is among the most profound and challenging questions in all of biology. How-ever, it is necessary that we work towards understanding the conditions in which life emerged on Earth to in-form our search for habitable environments and life elsewhere. The famous Urey Miller experiment2 verified that basic chemical ingredients for life could be produced under abiotic conditions, however the specific condi-tions on Earth in which life emerged is widely debated. There are multiple theories on where and in what con-ditions life developed, as well as many potential environments that could have contributed to the chemical in-ventory at the origin of life. As early as 1871, Charles Darwin proposed the idea of a “warm little pond” on early Earth’s surface containing an array of different chemical species, which could have resulted in the formation of the first biopolymers.3 UV light and dehydration/condensation reactions present in these systems would pro-mote conditions required for synthesizing molecules utilized in prebiotic chemistry.3-8 The concept that life originated around submarine hydrothermal vents has also gained traction, as there are striking similarities be-tween redox chemistry in these systems and the metabolism of modern living organisms.9-12 For an in-depth review on hydrothermal vent systems and their potential role in life’s origins, the reader is directed to William Martin et al. 2008.13 To aid in understanding these types of environments on Earth in an origin-of-life context, it is important that these environments be well-characterized, as scientists use these sites as analogues for extraterrestrial environ-ments due to their similarities with some conditions present on certain planetary bodies in our solar system.14 Successfully characterizing these environments requires appropriate analytical methodologies and instrumenta-tion, which presents a challenge to analytical chemists, as these environments are often chemically complex and present significant matrix effects (i.e., the Lost City hydrothermal system is alkaline and warm wet pools are hypersaline). Although analytical chemistry plays a key role across various sub-disciplines in astrobiology and planetary science, its role in effectively characterizing and understanding these terrestrial analogue envi-ronments is critical to informing the instrumentation we design and send to extraterrestrial bodies if we aim to one day detect life outside of Earth.15Our motivation in writing this Feature is to provide those interested in astrobiology an introduction to the history of and state of the art in analytical chemistry throughout our solar system from an astrobiological per-spective. We begin by briefly introducing the concepts of habitability and biosignatures, then present and dis-cuss the discoveries made throughout our solar system using analytical instrumentation and their implications in this context. We then present current plans for future missions throughout our solar system and discuss the challenges we face as analytical chemists in performing these investigations.