We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = [ 9.5 \pm 2.1 ] \times 10 ^ { -5 } via gravitational microlensing .
The planetary deviation was detected in real-time thanks to the high cadence of the MOA survey , real-time light curve monitoring and intensive follow-up observations .
A Bayesian analysis returns the stellar mass and distance at M _ { l } = 0.64 _ { -0.26 } ^ { +0.21 } M _ { \sun } and D _ { l } = 5.9 _ { -1.4 } ^ { +0.9 } kpc , respectively , so the mass and separation of the planet are M _ { p } = 20 _ { -8 } ^ { +7 } M _ { \oplus } and a = 3.3 _ { -0.8 } ^ { +1.4 } AU , respectively .
This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing , which now comprise four cold Neptune/Super-Earths , five gas giant planets , and another sub-Saturn mass planet whose nature is unclear .
The discovery of these ten cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN _ { pl } / d \log q \propto q ^ { -0.7 \pm 0.2 } with a 95 % confidence level upper limit of n < -0.35 ( where dN _ { pl } / d \log q \propto q ^ { n } ) .
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 .