Assessing the viability of biochemical networks across planets

Abstract

The concept of the origin of life implies that initially, life emerged from a non-living medium. If this medium was Earth's geochemistry, then that would make life, by definition, a geochemical process. The extent to which life on Earth today could subsist outside of the geochemistry from which it is embedded is poorly quantified. By leveraging large biochemical datasets in conjunction with planetary observations and computational tools, this research provides a methodological foundation for the quantitative assessment of our biology's viability in the context of other geospheres. Investigating a case study of alkaline prokaryotes in the context of Enceladus, we find that the chemical compounds observed on Enceladus thus far would be insufficient to allow even these extremophiles to produce the compounds necessary to sustain a viable metabolism. The environmental precursors required by these organisms provides a map for the compounds which should be prioritized for detection in future planetary exploration missions. The results of this framework have further consequences in the context of planetary protection, and hint that forward contamination may prove infeasible without meticulous intent.It is probable that the geochemical process known as life had already commenced when 2 today's oldest minerals began to crystallize. While there is widely accepted evidence 3 that the process of life has been present on Earth continuously for the past 3.4Gy [1], 4 the lack of evidence prior to this date has more to do with the paucity of 5 fossil-preserving rocks than concrete evidence of life's absence [14,32]. Despite the 6 biosphere's apparent interminable coexistence with the geosphere, there remain many 7 open questions on the matter of life persisting in Earth's absence [3,35], not to mention 8 the questions of Earth persisting in life's absence [21,23,24]. For example, Visionaries 9 dream of terraforming planets while program officers fret over "contaminating" 10 them [25,31,34]. While the terraformers tend to believe that seeding another planet 11 1/16 would require careful human or robotic (and usually Earth-assisted) cultivation, 12 planetary protection officers take the more conservative stance that a small, 13 semi-sterilized spacecraft of Earth origin could cause life to spill onto a planet in the 14 same way that a small perturbation to a super cooled liquid would cause the entire 15 volume to quickly crystallize. In both cases, there is the predominately implicit 16 assumption that Earth-life would be viable outside of the Earth. 17When life is viewed as a geologic process, this is a somewhat surprising assumption. 18 In the words of Morowitz et al., "the metabolic character of life is a planetary 19 phenomenon, no less than the atmosphere, hydrosphere, or geosphere" [30]. If this 20 "metabolic character of life" is truly a planetary phenomenon, does that imply that life 21 is inextricable from the planet through which it emerged? Or is it possible that an 22 97We ran the network expansion algorithm on the subs...