Bayesian evidence for the prevalence of waterworlds

TL;DR

This paper uses Bayesian analysis to argue that Earth's balanced land-water surface is unusual and that most habitable planets are likely waterworlds with over 90% ocean coverage, influenced by anthropic selection effects.

Contribution

It introduces a simple Bayesian model to assess the likelihood of Earth's surface conditions and predicts most habitable planets are water-dominated, supported by observational and simulation data.

Findings

Bayesian evidence supports anthropic selection effects on Earth's surface.

Most habitable planets are predicted to have over 90% ocean coverage.

Earth's balanced land-water surface is an outlier compared to typical habitable worlds.

Abstract

Should we expect most habitable planets to share the Earth's marbled appearance? For a planetary surface to boast extensive areas of both land and water, a delicate balance must be struck between the volume of water it retains and the capacity of its perturbations. These two quantities may show substantial variability across the full spectrum of water-bearing worlds. This would suggest that, barring strong feedback effects, most surfaces are heavily dominated by either water or land. Why is the Earth so finely poised? To address this question we construct a simple model for the selection bias that would arise within an ensemble of surface conditions. Based on the Earth's ocean coverage of 71%, we find substantial evidence (Bayes factor K ~ 6) supporting the hypothesis that anthropic selection effects are at work. Furthermore, due to the Earth's proximity to the waterworld limit, this model predicts that most habitable planets are dominated by oceans spanning over 90% of their surface area (95% credible interval). This scenario, in which the Earth has a much greater land area than most habitable planets, is consistent with results from numerical simulations and could help explain the apparently low-mass transition in the mass-radius relation.