MASSES, RADII, AND ORBITS OF SMALL KEPLER PLANETS: THE TRANSITION FROM GASEOUS TO ROCKY PLANETS

Abstract

We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm −3 , suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than ∼2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H 2 O).

SECURE MASS MEASUREMENTS FROM TRANSIT TIMING: 10 KEPLER EXOPLANETS BETWEEN 3 AND 8 M ⊕ WITH DIVERSE DENSITIES AND INCIDENT FLUXES

“…Tables 12 and 13 list the planetary masses and radii used in Figure 25. Note that the Marcy et al (2014) sample includes many nondetections and upper limits, which we do not plot. …”

“…Radial velocity (RV)spectroscopy has provided the bulk of mass measurements of transiting exoplanets (Batalha et al 2011;Winn et al 2011;Fressin et al 2012;Gillon et al 2012;Gautier et al 2012;Howard et al 2013;Pepe et al 2013;Weiss et al 2013;Haywood et al 2014;Marcy et al 2014;Dressing et al 2015). However, among subNeptune-mass planets, RV mass detections are limited to planets on short orbital periods, because the RV signal depends on the strength of planet-star interactions and declines with orbital distance.…”

“…However, among subNeptune-mass planets, RV mass detections are limited to planets on short orbital periods, because the RV signal depends on the strength of planet-star interactions and declines with orbital distance. Marcy et al (2014) conducted an RV survey of "bright" stars with short-period sub-Neptune-size planets in the Kepler field, and among planets below 10 M ⊕ they found strong detections up to around 16 days for Kepler-102 e (KOI-82.01) and , as well as useful upper limits within this mass range as far out as 69 days (Kepler-409 b, KOI-1925.01). Using the known sample of exoplanets characterized with RV, Rogers (2015) found that most planets larger than 1.6 R ⊕ with orbital periods up to ∼50 days are likely volatile rich.…”

An extreme planetary system around HD 219828

“…The figure shows that most multi-planet systems have mass ratios below 10, and only very few cases present mass ratios above 200. Except for HD 219828, other systems with a mass ratio above 200 include our solar system (not included in the plot), with a Jupiter-to-Mercury mass ratio of almost 4000 7 , GJ 676 A, an M-dwarf where Anglada-Escudé & Tuomi (2012) announced the presence of 2 + 2 super-Earths+jovian planets (see also Forveille et al 2011;Bonfils et al 2013a) with the highest mass ratio of 353, Kepler-94, with a hot Neptune and a moderately long-period (P ∼ 820 days) jovian companion (Marcy et al 2014, a mass ratio of 288, assuming co-planar orbits), and Kepler-454, a system composed of a short-period transiting super-Earth, one jovian gas giant with a period of 524 days, and an additional possible longer period gas giant (Gettel et al 2016, mass ratio of 207 assuming co-planar orbits). We note, however, that at least one of the low-mass planets in the Gl 676 A system has recently been disputed (e.g.…”

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

“…Most subNeptunes detected to date were discovered by the prime Kepler mission (2009)(2010)(2011)(2012)(2013). While Kepler provided a detailed measure of the distribution of planet radii, only a few tens of stars hosting sub-Neptunes were bright enough for secure mass measurements by current-generation precision radial velocity (RV) facilities (e.g., Marcy et al 2014). Many other planets have masses measured from transit timing variations (Agol et al 2005;Holman & Murray 2005), a technique that is limited to compact, multiplanet systems (e.g., Carter et al 2012;Hadden & Lithwick 2014).…”