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

Angie Wolfgang*, Eric Lopez

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The Kepler Mission has found thousands of planetary candidates with radii between 1 and 4 R-circle plus. 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-circle plus 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 similar to 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.

Original languageEnglish
Article number183
Number of pages22
JournalAstrophysical Journal
Volume806
Issue number2
DOIs
Publication statusPublished - 20 Jun 2015

Keywords

  • methods: statistical
  • planets and satellites: composition
  • POTENTIAL TRANSIT SIGNALS
  • FALSE-POSITIVE RATE
  • SUPER-EARTHS
  • EXTRASOLAR PLANETS
  • ECCENTRICITY DISTRIBUTION
  • GJ 1214B
  • RADIUS RELATIONSHIPS
  • TERRESTRIAL PLANETS
  • THERMAL EVOLUTION
  • STRUCTURE MODELS

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