Using the technique of gravitational microlensing, Fukui et al. (2015) present the discovery of a Saturn-mass planet with ~0.34 times the mass of Jupiter orbiting an M dwarf star with ~0.39 times the Sun’s mass at a projected separation of either ~0.74 AU (close model) or ~4.3 AU (wide model). The planet is identified as OGLE-2012-BLG-0563Lb and it is the 5th sub-Jupiter-mass (i.e. between 0.2 to 1.0 times the mass of Jupiter) to be found around an M dwarf star through gravitational microlensing. Although it is clear that there is a population of sub-Jupiter-mass planets around M dwarf stars, there appears to be a paucity of Jupiter-mass planets (i.e. planets with ~1 to 2 times the mass of Jupiter) around the same type of star. This suggests that planet formation via the core-accretion mechanism rarely produces Jupiter-mass planets around M dwarf stars due to the lack of material in the protoplanetary disk.
Fukui et al. (2015), “OGLE-2012-BLG-0563Lb: a Saturn-mass Planet around an M Dwarf with the Mass Constrained by Subaru AO imaging”, arXiv:1506.08850 [astro-ph.EP