BD+20 594 b - a Neptune-mass pure rock planet?

A Neptune-sized Exoplanet Consistent with a Pure Rock Composition
http://arxiv.org/abs/1601.07608

Quote :

We report the discovery of BD+20594b, a Neptune-sized exoplanet consistent with a pure rock composition, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission. The host star is a bright (V=11.04, Ks=9.37), slightly metal poor ([Fe/H]=−0.15±0.05 dex) solar analogue located at 152.1+9.7−7.4 pc from Earth, for which we find a radius of R∗=0.928+0.055−0.040R⊙ and a mass of M∗=0.961+0.032−0.029M⊙. A joint analysis of the K2 photometry and HARPS radial velocities reveal that the planet is in a ≈42 day orbit around its host star, has a radius of 2.23+0.14−0.11R⊕, and a mass of 16.3+6.0−6.1M⊕. The data at hand are most consistent with a pure rock composition with a low volatile content, potentially making it a rare exception among Neptune-sized exoplanets discovered so far.

Good news after hesitation with mass of k 10 c.We have planet which has low insolation and could not loose its envelope so it never had it. All parameters strikingly similar to k 10 c. I expect we will find small % of such planet among volatile rich.

BD 20594 b is not alone Kepler 131 b seems smaller
http://exoplanetarchive.ipac.caltech.edu//data/KeplerData/005/005695/005695396/dv/kplr005695396-001-20141002224145_dvs.pdf

The error bars still allow for substantial volatile content in the planet (see figure 8), especially if the planet has a metallic core in addition to the rocky component. Still, interesting discovery!

As regards Kepler-131b, the mass estimate is not in tommi59's link - but according to Marcy et al. (2014) the mass is 16.13±3.5 M_Earth. The lower radius of 2.17 R_Earth versus 2.41±0.20 R_Earth in Marcy et al. (2014) would push the density up somewhat from the value there.