The First Neptune Analog or Super-Earth with a Neptune-like Orbit: MOA-2013-BLG-605Lb
Résumé
We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, 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, a snow, which is similar to Neptune's separation of 11 a snow 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 {M}{{p}}={21}-7+6{M}\oplus orbiting a low-mass M-dwarf with a mass of {M}{{h}}={0.19}-0.06+0.05{M}⊙ , (II) a mini-Neptune with {M}{{p}}={7.9}-1.2+1.8{M}\oplus orbiting a brown dwarf host with {M}{{h}}={0.068}-0.011+0.019{M}⊙ , and (III) a super-Earth with {M}{{p}}={3.2}-0.3+0.5{M}\oplus orbiting a low-mass brown dwarf host with {M}{{h}}={0.025}-0.004+0.005{M}⊙ , which is slightly favored. The 3D planet-host separations are {4.6}-1.2+4.7 au, {2.1}-0.2+1.0 au, and {0.94}-0.02+0.67 au, which are {8.9}-1.4+10.5, {12}-1+7, or {14}-1+11 times larger than a snow for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems.