Exoplanets & Exomoons

Resonant Sub-Neptunes Are Puffier

By Keith Cowing
Status Report
June 28, 2024
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Resonant Sub-Neptunes Are Puffier
Full sample of 133 sub-Neptunes used in this study. The top-left panel shows the mass-radius relation. The (nearly)-resonant population is defined as ∆MMR <0.05 (see Eq. 1), while the non-resonant population is defined as ∆MMR >0.05. The black line is the sub-Neptune mass-radius relation from Parc et al. (2024). Other panels show the cumulative distributions for parameters of the planets or their host star. The pvalue given for each parameter is the probability that the distribution of that parameter is drawn form the same underlying distribution for the (nearly) resonant and non-resonant populations. The potential 2D correlation between parameters is explored in Fig. B.1. — astro-ph.EP

A systematic, population-level discrepancy exists between the densities of exoplanets whose masses have been measured with transit timing variations (TTVs) versus those measured with radial velocities (RVs).

Since the TTV planets are predominantly nearly resonant, it is still unclear whether the discrepancy is attributed to detection biases or to astrophysical differences between the nearly resonant and non resonant planet populations. We defined a controlled, unbiased sample of 36 sub-Neptunes characterised by Kepler, TESS, HARPS, and ESPRESSO.

We found that their density depends mostly on the resonant state of the system, with a low probability (of 0.002+0.010−0.001) that the mass of (nearly) resonant planets is drawn from the same underlying population as the bulk of sub-Neptunes.

Increasing the sample to 133 sub-Neptunes reveals finer details: the densities of resonant planets are similar and lower than non-resonant planets, and both the mean and spread in density increase for planets that are away from resonance. This trend is also present in RV-characterised planets alone. In addition, TTVs and RVs have consistent density distributions for a given distance to resonance.

We also show that systems closer to resonances tend to be more co-planar than their spread-out counterparts. These observational trends are also found in synthetic populations, where planets that survived in their original resonant configuration retain a lower density; whereas less compact systems have undergone post-disc giant collisions that increased the planet’s density, while expanding their orbits.

Our findings reinforce the claim that resonant systems are archetypes of planetary systems at their birth.

Adrien Leleu, Jean-Baptiste Delisle, Remo Burn, André Izidoro, Stéphane Udry, Xavier Dumusque, Christophe Lovis, Sarah Millholland, Léna Parc, François Bouchy, Vincent Bourrier, Yann Alibert, João Faria, Christoph Mordasini, Damien Ségransan

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.18991 [astro-ph.EP] (or arXiv:2406.18991v1 [astro-ph.EP] for this version)
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Submission history
From: Adrien Leleu
[v1] Thu, 27 Jun 2024 08:33:18 UTC (3,855 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻