Semi-empirical Estimates of the Cosmic Planet Formation Rate

TL;DR

This paper presents a semi-empirical, data-driven model to estimate the cosmic rate of planet formation, the distribution of habitable planets, and their potential to host civilizations across the universe.

Contribution

It introduces a novel semi-empirical framework combining galaxy evolution with planet formation recipes to estimate the cosmic planet formation rate and habitability.

Findings

Estimated 10^20 Earth-like planets in the universe.

Approximately 10^18 habitable Earths exist in the past lightcone.

A few 10^17 planets are older than Earth, suggesting low odds for extraterrestrial civilizations.

Abstract

We devise and exploit a data-driven, semi-empirical framework of galaxy formation and evolution, coupling it to recipes for planet formation from stellar and planetary science, to compute the cosmic planet formation rate, and the properties of the planets' preferred host stellar and galactic environments. We also discuss how the rates and formation sites of planets are affected when considering their habitability, and when including possible threatening sources related to star formation and nuclear activity. Overall, we conservatively estimate a cumulative number of some $10^{20}$ Earth-like planets and around $10^{18}$ habitable Earths in our past lightcone. Finally, we find that a few $10^{17}$ are older than our own Earth, an occurrence which places a loose lower limit a few $10^{-18}$ to the odds for a habitable world to ever hosting a civilization in the observable Universe.