Molecular complexity in astrophysical environments: From astrochemistry to “astrobiology”?

Abstract

A prebiotic molecule does not exist per-se, but only in a precise environmental contextAbstract. I present in this paper my own view about the intricate problem between the evolution of molecular complexity as observed from an astrophysicist point of view and its possible relation to the problem of the origin of life as we know it on Earth. Using arguments from observational astrophysics, I propose that life cannot really be based on other elements that the ones organizing our own so that other life forms based on totally different elemental and molecular processes are highly improbable. As a consequence terrestrial-type environments are probably the most favorable ones to life's "emergence" and subsequent evolution. Discussing molecular (organic) complexity, I show where this molecular complexity is located in astrophysical environments, mostly within inter/circumstellar solid state materials known as "grains" which, at least partly, end up in comets and asteroids and finally on planetary surfaces as meteorites. Considerations based on non directed laboratory simulations experiments, recent results regarding chiral asymmetry in potentially prebiotic matter and the possible explanation to the determinism about the choice of the L sign of the enantiomeric excesses in meteoritic amino acids, following a plausible astrophysical scenario, lead to the idea that the origin of life on Earth was indeed the result of a rather deterministic phenomenon, albeit difficult if not impossible to apprehend in its intimate mechanisms via a complete understanding of all the processes involved. Finally, the crucial point in supporting the idea of life's ubiquity and wide distribution in our Galaxy (or universe?) lies in the fact that planetary evolution, another astrophysical argument, is a major and very strong constraint for the development of life above its "minimal definition". Life, particularly the complex and evolved one, could be indeed very rare in our Galaxy, although the very large number of exoplanets may be a counter-argument to this statement. However, the deterministic nature of the processes at the origin of life on Earth, the only example we know, together with the progressively increased knowledge of the early conditions on telluric (exo)-planets and in particular those on our primitive Earth, where life did indeed appear, may render possible, in a near future, a semi-quantitative estimate of its occurrence in our Galaxy as well as major improvements in the field of prebiotic chemistry, possibly linked to the one of astrochemistry.

The Amino Acid Distribution in Laboratory Analogs of Extraterrestrial Organic Matter: A Comparison to CM Chondrites

“…The formation mechanisms and the evolution of organic matter in the solar system are still being debated (Aponte et al 2017). It is indeed uncertain if the organic material, or at least part of it, synthetized in the parent molecular cloud, survived throughout the protosolar disk phase and was later incorporated in the planetesimals that eventually formed comets and asteroids (Messenger 2000;d'Hendecourt 2011;Bertaux & Lallement 2017).…”

Data-Driven Astrochemistry: One Step Further within the Origin of Life Puzzle

“…The detected diverse set of molecules in space is statistically connected with the term molecular complexity [ 1 , 9 ]. As molecular complexity represents properties for a single molecular type, chemical diversity is proportional to the number of different compounds in a chemical system of interest.…”