HOW ROCKY ARE THEY? THE COMPOSITION DISTRIBUTION OF KEPLER’S SUB-NEPTUNE PLANET CANDIDATES WITHIN 0.15 AU

By A. Wolfgang, E. Lopez. 2014

142 citations recorded by the source corpus.

The Kepler Mission has found thousands of planetary candidates with radii between 1 and 4 R ⨁ ?> . These planets have no analogues in our own solar system, providing an unprecedented opportunity to understand the range and distribution of planetary compositions allowed by planet formation and evolution. A precise mass measurement is usually required to constrain the possible composition of an individual super-Earth-sized planet, but these measurements are difficult and expensive to make for the majority of Kepler planet candidates (PCs). Fortunately, adopting a statistical approach helps us to address this question without them. In particular, we apply hierarchical Bayesian modeling to a subsample of Kepler PCs that is complete for P < 25 ?> days and R pl > 1.2 ?> R ⨁ ?> and draw upon interior structure models that yield radii largely independent of mass by accounting for the thermal evolution of a gaseous envelope around a rocky core. Assuming the envelope is dominated by hydrogen and helium, we present the current-day composition distribution of the sub-Neptune-sized planet population and find that H+He envelopes are most likely to be ∼1% of these planets’ total masses with an intrinsic scatter of ±0.5 dex. We address the gaseous/rocky transition and illustrate how our results do not result in a one-to-one relationship between mass and radius for this sub-Neptune population; accordingly, dynamical studies that wish to use Kepler data must adopt a probabilistic approach to accurately represent the range of possible masses at a given radius.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0d9f982a3b2b9120ffba61e722b1760fd9c01ef5

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In Astronomy and Astrophysics

1. D. Charbonneau
2. Timothy Morton
3. J. Johnson
4. Andrew W. Howard
5. J. Winn
6. E. Petigura
7. G. Marcy
8. J. Owen

Citations in the corpus

• Core-powered mass-loss and the radius distribution of small exoplanets (2017, background): “A commonly suggested structure that explains the low densities of these planets is a rocky core engulfed by a voluminous gas atmosphere of several percent in mass (e.g. Lopez et al. 2012; Lissauer et al. 2013; Wolfgang & Lopez 2015).”
• Identifying Exoplanets with Deep Learning: A Five-planet Resonant Chain around Kepler-80 and an Eighth Planet around Kepler-90 (2017, background): “…et al. 2016; Thompson et al. 2017; Rowe et al. 2014; Morton et al. 2016), and significantly improved our understanding of the population of small planets in the inner parts of planetary systems (Marcy et al. 2014; Howard et al. 2012; Youdin 2011; Dressing et al. 2015; Wolfgang & Lopez 2015).”
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets (2017, background): “For this reason, it has been suggested that the radii of sub-Neptune-size planets, along with knowledge of the irradiation history, would be sufficient to estimate bulk composition without additional information (Lopez & Fortney 2013; Wolfgang & Lopez 2015).”
• Atmospheric characterization of Proxima b by coupling the Sphere high-contrast imager to the Espresso spectrograph (2016, background): “Despite many recent advances (e.g. Rogers 2015; Dressing et al. 2015; Wolfgang & Lopez 2015), there is no generally-accepted average mass-radius relation for exoplanets.”
• Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation (2017, result): “A clear compositional gradient with increasing planet radius is seen, similar to earlier studies (e.g., Marcy et al. 2014; Rogers 2015; Wolfgang & Lopez 2015): for R .”
• The California-Kepler Survey. V. Peas in a Pod: Planets in a Kepler Multi-planet System Are Similar in Size and Regularly Spaced (2017, background): “…there is large scatter in the planet masses with respect to these mean empirical relations (Marcy et al. 2014; Weiss & Marcy 2014; Rogers 2015; Wolfgang & Lopez 2015; Chen & Kipping 2017), we have no reliable basis for deciding which planet masses should be higher or lower than the mean, and…”
• The CARMENES Search for Exoplanets around M Dwarfs: A Low-mass Planet in the Temperate Zone of the Nearby K2-18 (2018, result): “This is in agreement with Rogers (2015) and Wolfgang & Lopez (2015), who showed that most planets with radii larger than 1.6 R⊕ are not rocky.”
• CHARACTERIZING K2 PLANET DISCOVERIES: A SUPER-EARTH TRANSITING THE BRIGHT K DWARF HIP 116454 (2014, result): “We note that this envelope fraction is consistent with the population of Kepler super-Earth/sub-Neptune sized planets studied by Wolfgang & Lopez (2014), who found the envelope fraction of these candidates to be distributed around 1% with a scatter of 0.5 dex.”
• THE MASS OF Kepler-93b AND THE COMPOSITION OF TERRESTRIAL PLANETS (2014, methodology): “These planets appear to have a diversity of compositions that is not well-explained by a single mass-radius relation (Wolfgang & Lopez 2014).”
• The California-Kepler Survey. I. High-resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets (2017, background): “Marcy et al. (2014) measured the masses of 49 planets and found evidence for a transition from rock- to gas-dominated compositions with increasing planet size (Weiss & Marcy 2014; Rogers 2015; Wolfgang & Lopez 2015).”
• PROBABILISTIC MASS–RADIUS RELATIONSHIP FOR SUB-NEPTUNE-SIZED PLANETS (2015, methodology): “…should exist: thermally evolved rock-hydrogen sub-Neptune internal structure models yield radii mostly indepen- dent of mass (Lopez & Fortney 2014), which produces significant mass-radius scatter when a distribution of gaseous mass fractions is present in the population (Wolfgang & Lopez 2015).”
• BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS (2015, background): “Kepler super-Earths have core masses large enough to nucleate gas giants, yet have atmospheres that are modest by mass (e.g., Lopez & Fortney 2014; Wolfgang & Lopez 2015).”
• TERRESTRIAL PLANET OCCURRENCE RATES FOR THE KEPLER GK DWARF SAMPLE (2015, background): “The integral range of 20% is within the expectations for the regime of rocky terrestrial planets (Rogers 2015; Wolfgang & Lopez 2014).”
• The California-Kepler Survey. II. Precise Physical Properties of 2025 Kepler Planets and Their Host Stars (2017, background): “…Fressin et al. 2013; Petigura et al. 2013) and planetary architectures (Lissauer et al. 2011; Fabrycky et al. 2014), and when coupled with spectroscopy, enabled determination of planet masses, densities, and interiors (Marcy et al. 2014; Weiss & Marcy 2014; Rogers 2015; Wolfgang & Lopez 2015).”