Oxygen-Free Biochemistry: The Putative CHN Foundation for Exotic Life in a Hydrocarbon World?

Abstract

Since Earth's biochemistry is carbon-based and water-borne, the main strategies for searching for life elsewhere are "follow the carbon" and "follow the water." Recently, however, there is a growing focus on the prospect that putative exotic life on other planets could rely on unearthly biochemistries. Here, we hypothesize a novel oxygen-free organic chemistry for supporting potential exotic biosystems, which is named CHN biochemistry. This oxygen-free CHN biochemistry starts from simple oxygen-free species (including hydrocarbons, hydrogen cyanide, and nitriles) and produces a range of functional macromolecules that may function in similar ways to terran macromolecules, such as sugars (cyanosugars), acids (cyanoacids), amino acids (amino cyanoacids), and nucleobases (cyanonucleobases). These CHN macromolecules could further interact with each other to generate higher "cyanoester" and "cyanoprotein" systems. In addition, theoretical calculations indicate that the energy changes of some reactions are consistent with their counterparts in Earth's biochemistry. The CHN biochemistry-based life would be applicable in habitats with a low bioavailability of oxygen, such as the alkane lakes of Titan and non-aquatic liquids on extrasolar bodies. Key Words: Oxygen-free biochemistry-Titan-Hydrocarbons-Hydrogen cyanide-Nitriles. Astrobiology 17, 1173-1181.

Defining Lyfe in the Universe: From Three Privileged Functions to Four Pillars

“…), if exobiology exists on Titan, it would have emerged and evolved in an environment incredibly dissimilar to Earth. Major environmental differences include: extremely low surface temperatures of ∼94 K (resulting in exotic Van der Waals-driven organic chemistry [100,101]); a lack of available oxygen for biochemistry (resulting in hypotheses for N-substituted biochemistries [102]); and a nonpolar CH 4 -C 2 H 6 solvent (resulting in speculations for alternative membrane structures).…”

Asymptotic burnout and homeostatic awakening: a possible solution to the Fermi paradox?

“…An analogy can be drawn to exo-biochemistries: Because 'chemical space' is huge, some astrobiologists have hypothesized that alien biochemistries could take many different forms, and that the particulars of our biochemistry were influenced by the specific chemical environment on the early Earth as well as historical contingencies of our single evolutionary path (e.g. [60][61][62][63]). Similarly, perhaps 'cultural space' is huge, resulting in technological civilizations whose self-organizing dynamics appear as foreign to us as a lyfe form that doesn't use H 2 O as its solvent.…”

Titan: Earth-like on the Outside, Ocean World on the Inside

“…Finally, Titan's lakes and seas of liquid hydrocarbons offer a unique opportunity to investigate whether the solvent necessary for biochemistry must be water. Theoretical considerations suggest alternative chemistries are possible (Benner et al 2004;Lv et al 2017) and the abundance of solid and liquid organic molecules available on the surface and lack of UV radiation make the surface of Titan an advantageous place for exploring the possibility of a true second genesis (Lunine & Lorenz 2009;Lunine 2010;McKay 2016). Theoretical investigations are exploring both the possibilities for lipid membrane-like structures in low temperature environments and whether cell membranes are even necessary (Palmer et al 2017;Stevenson et al 2015;Rahm et al 2016;Sandström & Rahm 2020).…”