Kepler-289 / PH3, Multi-planet system with measured densities

Planet Hunters VII. Discovery of a New Low-Mass, Low-Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)
http://arxiv.org/abs/1410.8114

Quote :

We report the discovery of one newly confirmed planet (P=66.06 days, RP=2.68±0.17R⊕) and mass determinations of two previously validated Kepler planets, Kepler-289 b (P=34.55 days, RP=2.15±0.10R⊕) and Kepler-289-c (P=125.85 days, RP=11.59±0.10R⊕), through their transit timing variations (TTVs). We also exclude the possibility that these three planets reside in a 1:2:4 Laplace resonance. The outer planet has very deep (∼1.3), high signal-to-noise transits, which puts extremely tight constraints on its host star's stellar properties via Kepler's Third Law. The star PH3 is a young (∼1 Gyr as determined by isochrones and gyrochronology), Sun-like star with M∗=1.08±0.02M⊙, R∗=1.00±0.02R⊙, and Teff=5990±38 K. The middle planet's large TTV amplitude (∼5 hours) resulted either in non-detections or inaccurate detections in previous searches. A strong chopping signal, a shorter period sinusoid in the TTVs, allows us to break the mass-eccentricity degeneracy and uniquely determine the masses of the inner, middle, and outer planets to be M=7.3±6.8M⊕, 4.0±0.9M⊕, and M=132±17M⊕, which we designate PH3 b, c, and d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low density, ρ=1.2±0.3 g/cm3 for a planet of its mass, requiring a substantial H/He atmosphere of 2.1+0.8−0.3 by mass, and joins a growing population of low-mass, low-density planets.

Nevertheless planet b is quite dense receiving much smaller stellar insolation than kepler 11 b

Another case of nomenclature mismatch, PH3 d=Kepler-289 c. Not sure why they didn't bring the designations in line before publishing the paper.

Unsurprisingly it has been added to the NASA archive as Kepler-289 d.