2021ApJ...920L..34M -
Astrophys. J., 920, L34-L34 (2021/October-3)
Split peas in a pod: intra-system uniformity of super-Earths and sub-Neptunes.
MILLHOLLAND S.C. and WINN J.N.
Abstract (from CDS):
The planets within compact multiplanet systems tend to have similar sizes, masses, and orbital period ratios, like "peas in a pod." This pattern was detected when considering planets with radii between 1 and 4 R⊕. However, these same planets show a bimodal radius distribution, with few planets between 1.5 and 2 R⊕. The smaller "super-Earths" are consistent with being stripped rocky cores, while the larger "sub-Neptunes" likely have gaseous H/He envelopes. Given these distinct structures, it is worthwhile to test for intra-system uniformity separately within each category of planets. Here, we find that the tendency for intra-system uniformity is twice as strong when considering planets within the same size category than it is when combining all planets together. The sub-Neptunes tend to be 1.7–0.3+0.6 times larger than the super-Earths in the same system, corresponding to an envelope mass fraction of about 2.6% for a 5 M⊕ planet. For the sub-Neptunes, the low-metallicity stars are found to have planets with more equal sizes, with modest statistical significance (p ∼ 0.005). There is also a modest (∼2σ) tendency for wider-orbiting planets to be larger, even within the same size category.
Abstract Copyright:
© 2021. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Exoplanets - Super Earths - Mini Neptunes - Exoplanet systems
Simbad objects:
48
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