On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances

TL;DR

This paper explores how high radionuclide abundances can enable worlds outside traditional habitable zones to sustain liquid solvents like water or ethane over geological timescales, potentially detectable by JWST.

Contribution

It identifies conditions under which high radionuclide levels allow non-traditional habitable worlds to maintain liquid solvents for long periods.

Findings

Super-Earths with radionuclide abundances >10^3 times Earth's can host long-lived water oceans.

Less restrictive radionuclide levels (>10^2 times Earth's) may sustain ethane oceans.

Such worlds could be detectable by JWST within 10 days at 12.8 μm if they are younger than 1 Gyr.

Abstract

The presence of a liquid solvent is widely regarded as an essential prerequisite for habitability. We investigate the conditions under which worlds outside the habitable zones of stars are capable of supporting liquid solvents on their surface over geologically significant timescales via combined radiogenic and primordial heat. Our analysis suggests that super-Earths with radionuclide abundances that are $\gtrsim 10^3$ times higher than Earth can host long-lived water oceans. In contrast, the requirements for long-lived ethane oceans, which have been explored in the context of alternative biochemistries, are less restrictive: relative radionuclide abundances of $\gtrsim 10^2$ could be sufficient. We find that this class of worlds might be detectable ($10\sigma$ detection over $\sim 10$ days integration time at $12.8$ $\mu$m) in principle by the James Webb Space Telescope at distances of $\sim 10$ pc if their ages are $\lesssim 1$ Gyr.