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Kepler planets: a tale of evaporation

25 Pith papers cite this work, alongside 766 external citations. Polarity classification is still indexing.

25 Pith papers citing it
766 external citations · Pith
abstract

(Abridged) Inspired by the Kepler planet discoveries, we consider the thermal contraction of planets close to their parent star, under the influence of evaporation. The mass-loss rates are based on hydrodynamic models of evaporation that include both X-ray and EUV irradiation. We find that only low-mass planets with hydrogen envelopes are significantly affected by evaporation, with evaporation being able to remove massive hydrogen envelopes inward of 0.1 AU for Neptune-mass objects. We construct a theoretical population of planets with varying core masses, envelope masses, orbital separations, and stellar spectral types, and compare these against the sizes and densities measured for low-mass planets, both in the Kepler mission and from radial velocity surveys. This exercise leads us to conclude that evaporation is the driving force of evolution for close-in Kepler planets. In fact, some 50% of the Kepler planet candidates may have been significantly eroded. Evaporation explains two striking correlations observed in these objects: a lack of large radius/low density planets close to the stars, and a bimodal distribution in planet sizes with a deficit of planets around 2R_E. Planets that have experienced high X-ray exposures are generally smaller than this size, and those with lower X-ray exposures are typically larger. A bimodal distribution is naturally explained by the evaporation model, where, depending on their X-ray exposure, close-in planets can either hold on to hydrogen envelopes 1% in mass, or be stripped entirely. To quantitatively reproduce the observed features, we argue that not only do low-mass Kepler planets need to be made of rocky cores overlaid with hydrogen envelopes, but few of them should have initial masses above 20 M_E, and the majority of them should have core masses of a few Earth masses.

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2026 25

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representative citing papers

The Effect of Adiabatic Index on Radius Evolution and the Mass Loss

astro-ph.EP · 2026-06-15 · unverdicted · novelty 4.0

Varying the adiabatic index from 1.2 to 1.4 in exoplanet evolution models shows that higher gamma produces puffier initial envelopes that contract faster with accelerated mass loss, so using gamma=1.4 overestimates mass-loss effects on young planets.

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Showing 25 of 25 citing papers.