DENSITIES AND ECCENTRICITIES OF 139KEPLERPLANETS FROM TRANSIT TIME VARIATIONS

Abstract

We extract densities and eccentricities of 139 sub-Jovian planets by analyzing transit time variations (TTVs) obtained by the Kepler mission through Quarter 12. We partially circumvent the degeneracies that plague TTV inversion with the help of an analytical formula for the TTV. From the observed TTV phases, we find that most of these planets have eccentricities of order a few percent. More precisely, the r.m.s. eccentricity is 0.018 +0.005 −0.004 , and planets smaller than 2.5R ⊕ are around twice as eccentric as those bigger than 2.5 R ⊕ . We also find a best-fit density-radius relationship ρ ≈ 3 g/cm 3 × (R/3R ⊕ ) −2.3 for the 56 planets that likely have small eccentricity and hence small statistical correction to their masses. Many planets larger than 2.5R ⊕ are less dense than water, implying that their radii are largely set by a massive hydrogen atmosphere.

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

“…An even narrower eccentricity distribution (of characteristic width σ = 0.02) was found for a sample of compact multiplanet systems with TTVs by Hadden & Lithwick (2014). While this is the most relevant sample for our purposes, we adopt the wider prior to test where the TTVs can provide tight constraints on eccentricity.…”

“…These are accurate to firstorder in planet-star mass ratios, firstorder in eccentricity, and assume co-planarity. Accuracy to first order in eccentricities is satisfied if 9 http://exoplanetarchive.ipac.caltech.edu/ eccentricities are 0.1, which is likely given the narrow dispersion in eccentricities among Kepler's multiplanet systems Hadden & Lithwick 2014). Where there is a second-order dependence on eccentricity, e.g., nearsecond-order mean motion resonances, the solutions of Deck & Agol (2015b) provide an even more general analysis of TTV frequencies.…”

“…Two transiting planets with anticorrelated TTVs are known to orbit Kepler-57 (Steffen et al 2012b;Hadden & Lithwick 2014). Given their proximity to the first-order 2:1 mean motion resonance, their expected TTV period of 456 days is easily seen in Figure 8.…”

Synergies Between Asteroseismology and Exoplanetary Science

“…Traditionally, eccentricities can be measured through Doppler velocities, secondary transits, or transit-timing variations. However, these methods are either only applicable for relatively large gas-giant planets, or a small subset of multiplanet systems for which effects of eccentricity and mass can be successfully disentangled (e.g., Lithwick et al, 2012;Hadden & Lithwick, 2014).…”

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

“…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).…”