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

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.

Piero Madau

Comments: 14 pages, 8 figures, submitted to AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2309.11927 [astro-ph.EP] (or arXiv:2309.11927v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2309.11927
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Submission history
From: Piero Madau
[v1] Thu, 21 Sep 2023 09:42:19 UTC (1,982 KB)
https://arxiv.org/abs/2309.11927
Astrobiology