MOA-2013-BLG-605Lb: a Neptune Analog Around an M Dwarf

The First Cold Neptune Analog Exoplanet: MOA-2013-BLG-605Lb

Authors:

Sumi et al

Abstract:

We present the discovery of the first Neptune analog exoplanet, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at 9∼14 times the expected position of the snow-line, asnow, which is similar to Neptune's separation of 11asnow from the Sun. The planet/host-star mass ratio is q=(3.6±0.7)×10−4 and the projected separation normalized by the Einstein radius is s=2.39±0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy". The three models have (i) a Neptune-mass planet with a mass of Mp=21+6−7Mearth orbiting a low-mass M-dwarf with a mass of Mh=0.19+0.05−0.06M⊙, (ii) a mini-Neptune with Mp=7.9+1.8−1.2Mearth orbiting a brown dwarf host with Mh=0.068+0.019−0.011M⊙ and (iii) a super-Earth with Mp=3.2+0.5−0.3Mearth orbiting a low-mass brown dwarf host with Mh=0.025+0.005−0.004M⊙. The 3-D planet-host separations are 4.6+4.7−1.2 AU, 2.1+1.0−0.2 AU and 0.94+0.67−0.02 AU, which are 8.9+10.5−1.4, 12+7−1 or 14+11−1 times larger than asnow for these models, respectively. The Keck AO observation confirm that the lens is faint. This discovery suggests that Neptune-like planets orbiting at ∼11asnow are quite common. They may be as common as planets at ∼3asnow, where microlensing is most sensitive, so processes similar to the one that formed Uranus and Neptune in our own Solar System may be quite common in other solar systems.