A COLD NEPTUNE-MASS PLANET OGLE-2007-BLG-368Lb: COLD NEPTUNES ARE COMMON

Abstract

We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet–star mass ratio of q = [9.5 ± 2.1] × 10−5 via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the Microlensing Observations in Astrophysics survey, real-time light-curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at Ml = 0.64+0.21 −0.26M andDl = 5.9+0.9 −1.4 kpc, respectively, so themass and separation of the planet areMp = 20+7 −8M⊕ and a = 3.3+1.4 −0.8 AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprises four cold Neptune/super-Earths, five gas giant planets, and another sub- Saturn mass planet whose nature is unclear. The discovery of these 10 cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dNpl/d log q ∝ q−0.7±0.2 with a 95% confidence level upper limit of n < −0.35 (where dNpl/d log q ∝ qn). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level.