Beyond the Drake Equation: A Time-Dependent Inventory of Habitable Planets and Life-Bearing Worlds in the Solar Neighborhood

TL;DR

This paper presents a time-dependent mathematical framework for studying exoplanet populations and potential life in the solar neighborhood, revealing episodic planet formation, abundance of habitable planets, and implications for life emergence.

Contribution

It introduces a novel differential equations-based model linking star formation, metallicity, and habitability over cosmic time, advancing exoplanet and astrobiology research.

Findings

Episodic formation of exoplanets starting 11 Gyr ago.

Approximately 11,000 Earth-size habitable planets within 100 pc.

Potential for life-bearing planets to be within 20 pc of Earth.

Abstract

We introduce a mathematical framework for statistical exoplanet population and astrobiology studies that may help directing future observational efforts and experiments. The approach is based on a set of differential equations and provides a time-dependent mapping between star formation, metal enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemo-population history of the solar neighborhood. Our results are summarized as follows: 1) the formation of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about 11 Gyr ago; 2) within 100 pc from the Sun, there are as many as 11,000 (eta/0.24) Earth-size planets in the habitable zone ("temperate terrestrial planets" or TTPs) of K-type stars. The solar system is younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and was triggered by an external agent; 3) the metallicity modulation of the giant planet occurrence rate results in a later typical formation time, with TTPs outnumbering giant planets at early times; 4) the closest, life-harboring Earth-like planet would be < 20 pc away if microbial life arose as soon as it did on Earth in > 1 % of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also old, as it would have emerged more than 8 Gyr ago in about one third of all life-bearing planets today. Older Earth analogs are more likely to have developed sufficiently complex life capable of altering the environment and producing detectable oxygenic biosignatures.