We present the confirmation of a small , moderately-irradiated ( F = 155 \pm 7 F _ { \oplus } ) Neptune with a substantial gas envelope in a P =11.8728787 \pm 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 \pm 0.082 R _ { \oplus } .
We acquired 95 high-resolution spectra with TNG/HARPS-N , enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0 \pm ^ { 3.1 } _ { 2.8 } M _ { \oplus } 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 .