Seeding Biochemistry on Other Worlds: Enceladus as a Case Study

Abstract

The Solar System is becoming increasingly accessible to exploration by robotic missions to search for life. However, astrobiologists currently lack well-defined frameworks to quantitatively assess the chemical space accessible to life in these alien environments. Such frameworks will be critical for developing concrete predictions needed for future mission planning, both to determine the potential viability of life on other worlds and to anticipate the molecular biosignatures that life could produce. Here, we describe how uniting existing methods provides a framework to study the accessibility of biochemical space across diverse planetary environments. Our approach combines observational data from planetary missions with genomic data catalogued from across Earth and analyzed using computational methods from network theory. To demonstrate this, we use 307 biochemical networks generated from genomic data collected across Earth and “seed” these networks with molecules confirmed to be present on Saturn's moon Enceladus. By expanding through known biochemical reaction space starting from these seed compounds, we are able to determine which products of Earth's biochemistry are, in principle, reachable from compounds available in the environment on Enceladus, and how this varies across different examples of life from Earth (organisms, ecosystems, planetary-scale biochemistry). While we find that none of the 307 prokaryotes analyzed meet the threshold for viability, the reaction space covered by this process can provide a map of possible targets for detection of Earth-like life on Enceladus, as well as targets for synthetic biology approaches to seed life on Enceladus. In cases where biochemistry is not viable because key compounds are missing, we identify the environmental precursors required to make it viable, thus providing a set of compounds to prioritize for detection in future planetary exploration missions aimed at assessing the ability of Enceladus to sustain Earth-like life or directed panspermia.

Scaling laws in enzyme function reveal a new kind of biochemical universality

“…In network expansion, one starts from a “seed set” of handfuls of compounds and reacts them; the products produced are then added to the list of possible reactants, and the algorithm is iteratively repeated until no new products are formed. It has been used to study early life ( 23 , 24 ) and the evolution of Earth’s biochemistry over geological timescales ( 22 ), as well as on other planetary bodies ( 25 ).…”

A Cosmological Neuroscientific Approach to the Soul of Multiverse

“…Such broadened cosmology would consider Rabindranath Tagore (1931)'s note on evolution that "…A multitude of cells were bound together into a larger unit, not through aggregation, but through a marvelous quality of complex interrelationship…the creative principle of unity, the divine mystery of existence…" Then, admitting that this "mystery" is difficult to explain with abiogenesis theories, the discipline would turn to the Crick & Orgel (1973) idea on Directed Panspermia and examine its claim that "…It is a little surprising that organisms with somewhat different codes do not coexist. The universality of the code follows naturally from an 'infective' theory of the origins of life…" In fact, we on Earth are already thinking about "seeding biochemistry" into the subsurface ocean of Saturn's moon Enceladus (Smith et al, 2021).…”

Metabolic compatibility and the rarity of prokaryote endosymbioses

“…In addition to modeling systems that can be experimentally validated, they have also been used to address questions that extend beyond our knowledge of and application to extant life. For example, metabolic models coupled with the network expansion method have been used to propose possibilities for early metabolism on Earth [31], network structure scaling with size [32], and what metabolisms are likely to exist in distinct planetary conditions [33]. Such generality and flexibility is ideal for our interest in exploring the challenges of an event that is possible but rarely seen.…”