THE MASS-RADIUS RELATION FOR 65 EXOPLANETS SMALLER THAN 4 EARTH RADII
- B-20 Hearst Field Annex, Astronomy Department, University of California, Berkeley, CA 94720 (United States)
We study the masses and radii of 65 exoplanets smaller than 4 R {sub ⊕} with orbital periods shorter than 100 days. We calculate the weighted mean densities of planets in bins of 0.5 R {sub ⊕} and identify a density maximum of 7.6 g cm{sup –3} at 1.4 R {sub ⊕}. On average, planets with radii up to R {sub P} = 1.5 R {sub ⊕} increase in density with increasing radius. Above 1.5 R {sub ⊕}, 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 {sub ⊕}, we find ρ{sub P} = 2.43 + 3.39(R {sub P}/R {sub ⊕}) g cm{sup –3} for R {sub P} < 1.5 R {sub ⊕}, which is consistent with rocky compositions. For 1.5 ≤ R {sub P}/R {sub ⊕} < 4, we find M {sub P}/M {sub ⊕} = 2.69(R {sub P}/R {sub ⊕}){sup 0.93}. The rms of planet masses to the fit between 1.5 and 4 R {sub ⊕} is 4.3 M {sub ⊕} with reduced χ{sup 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.
- DOE Contract Number:
- Grant DGE 1106400
- OSTI ID:
- 22363961
- Journal Information:
- Astrophysical Journal Letters, Vol. 783, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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