Resonant sub-Neptunes are puffier
arxiv(2024)
摘要
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_-0.001^+0.010) 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.
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