The Influence of Age on the Relative Frequency of Super-Earths and Sub-Neptunes

TL;DR

This study investigates how the ratio of super-Earths to sub-Neptunes changes with stellar age, providing insights into atmospheric loss processes affecting small exoplanets over billions of years.

Contribution

It presents observational evidence of the age-dependent increase in super-Earth to sub-Neptune ratio, constraining atmospheric loss timescales with a large Kepler dataset.

Findings

Super-Earth to sub-Neptune ratio increases monotonically from 1-10 Gyr.

Results agree with models including photoevaporation effects.

Trend persists after accounting for observational biases.

Abstract

There is growing evidence that the population of close-in planets discovered by the Kepler mission was sculpted by atmospheric loss, though the typical timescale for this evolution is not well-constrained. Among a highly complete sample of planet hosts of varying ages the age-dependence of the relative fraction of super-Earth and sub-Neptune detections can be used to constrain the rate at which some small planets lose their atmospheres. Using the California-Kepler Survey (CKS) sample, we find evidence that the ratio of super-Earth to sub-Neptune detections rises monotonically from 1-10 Gyr. Our results are in good agreement with an independent study focused on stars hotter than the Sun, as well as with forward modeling simulations incorporating the effects of photoevaporation and a CKS-like selection function. We find the observed trend persists even after accounting for the effects of completeness or correlations between age and other fundamental parameters.