Year: 2014
Type: article
Abstract: We study the masses and radii of 65 exoplanets smaller than 4 R ⊕ with orbital periods shorter than 100 days. We calculate the weighted mean densities of planets in bins of 0.5 R ⊕ and identify a density maximum of 7.6 g cm −3 at 1.4 R ⊕ . On average, planets with radii up to R P = 1.5 R ⊕ increase in density with increasing radius. Above 1.5 R ⊕ , the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core. Including the solar system terrestrial planets with the exoplanets below 1.5 R ⊕ , we find ρ P = 2.43 + 3.39( R P / R ⊕ ) g cm −3 for R P < 1.5 R ⊕ , which is consistent with rocky compositions. For 1.5 ⩽ R P / R ⊕ < 4, we find M P / M ⊕ = 2.69( R P / R ⊕ ) 0.93 . The rms of planet masses to the fit between 1.5 and 4 R ⊕ is 4.3 M ⊕ with reduced χ 2 = 6.2. The large scatter indicates a diversity in planet composition at a given radius. The compositional diversity can be due to planets of a given volume (as determined by their large H/He envelopes) containing rocky cores of different masses or compositions.
Authors: Lauren M. Weiss, Geoffrey W. Marcy
Institution: University of California, Berkeley
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1967414563