Chemical Complexity and Prevalence of Life in the Universe: A New Method for the Estimation of Key Terms of Drake Equation

TL;DR

This paper introduces a novel method to estimate the prevalence of life in the universe by relating chemical complexity to cosmic matter hierarchy, providing new quantitative predictions for the number of life-bearing planets.

Contribution

It presents a new approach linking chemical complexity to the likelihood of life, offering quantitative estimates for life prevalence in the Milky Way.

Findings

Inverse logarithmic relationship between chemical complexity and cosmic environment mass fraction

Estimated 1.3 to 1.6 x 10^4 planets with minimal life in the Milky Way

Defined minimal chemical complexity for life based on experimental studies

Abstract

I describe a new method of estimating the prevalence of life in the Universe, based on the fact that more chemically complex environments are more rare. The paper makes three main claims: (1) There is a statistically significant (inverse) relationship between chemical complexity (quantified as the number of different types of molecules present in a given environment) and mass fraction for the successively smaller environments in the hierarchy of cosmic matter (extragalactic medium, interstellar clouds, dense cores, planetary systems, their icy fraction etc.) that is well described by a logarithmic law. (2) Minimal chemical complexity of life can be roughly defined, based on existing studies in vitro and in silico, both bottom-up (designing increasingly complex chemical systems) and top-down (simplifying minimal organisms). (3) Thus, one can estimate the fraction of the total mass density of the Universe that resides in reservoirs of chemical complexity estimated as being minimal for life. This is then translated, through simple statistical models of planetary systems, into the number of planets in a single Milky Way-sized galaxy that have, on their surface, reservoirs of biogenic chemical complexity. Two best models give the estimates of 1.6 (more complex minimal life) and 1.3e4 (slightly less complex minimal life) as the predicted upper bound for the number of instances of life per our Galaxy.