Growth model interpretation of planet size distribution.

Area of Science:

• Exoplanetary Science
• Planetary Composition
• Astrophysics

Background:

• The Kepler mission precisely measured radii and orbital periods for over 4,000 exoplanets.
• Exoplanet radii exhibit a bimodal distribution, with peaks for smaller rocky and larger intermediate-size planets.
• Ground-based observations constrain densities, offering insights into bulk compositions and internal structures.

Purpose of the Study:

• To resolve the ambiguity in the internal composition of intermediate-size exoplanets (2-4 Earth radii).
• To determine if these planets are gas dwarfs or water worlds.

Main Methods:

• Utilized a planetary growth model.
• Conducted Monte Carlo simulations to analyze composition scenarios.
• Constrained gas envelope mass percentages for planets in the 2-4 Earth radii range.

Main Results:

• Planets with radii matching the second peak of the exoplanet radius distribution (approx. 2.5 Earth radii) and masses of 10-15 Earth masses are consistent with a half-ice, half-rock composition.
• Intermediate-size planets require minimal gas envelopes (a few mass percentage points) regardless of core composition.
• The study demonstrates that many intermediate-size planets are likely "water worlds".

Conclusions:

• The composition of intermediate-size exoplanets is predominantly water-rich.
• The findings challenge the prevalence of gas dwarfs in this size range.
• This research refines our understanding of exoplanet diversity and formation.