An Accurate Mass Determination for Kepler-1655b, a Moderately Irradiated World with a Significant Volatile Envelope

摘要

We present the confirmation of a small, moderately irradiated (F = 155 ± 7 F⊕) Neptune with a substantial gas envelope in a P?=11.8728787?±?0.0000085 day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b’s radius to be 2.213?±?0.082 R⊕. We acquired 95 high-resolution spectra with Telescopio Nazionale Galileo/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0 2.8 M ?3.1 ? via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98% confidence. Kepler-1655b?falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further.