We present the discovery of the first Neptune analog exoplanet or super-Earth with 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 $9\sim 14$ times the expected position of the snow-line, $a_{ \rm snow}$, which is similar to Neptune's separation of $ 11\,a_{ \rm snow}$ from the Sun. The planet/host-star mass ratio is $q=(3.6\pm0.7)\times 10^{ -4}$ and the projected separation normalized by the Einstein radius is $s=2.39\pm0.05$. 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 $M_{ \rm p}=21_{ -7}^{ +6} M_{ Earth}$ orbiting a low-mass M-dwarf with a mass of $M_{ \rm h}=0.19_{ -0.06}^{ +0.05} M_\odot$, (ii) a mini-Neptune with $M_{ \rm p}= 7.9_{ -1.2}^{ +1.8} M_{ Earth}$ orbiting a brown dwarf host with $M_{ \rm h}=0.068_{ -0.011}^{ +0.019} M_\odot$ and (iii) a super-Earth with $M_{ \rm p}= 3.2_{ -0.3}^{ +0.5} M_{ Earth}$ orbiting a low-mass brown dwarf host with $M_{ \rm h}=0.025_{ -0.004}^{ +0.005} M_\odot$ which is slightly favored. The 3-D 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 $a_{ \rm snow}$ for these models, respectively. The Keck AO observation confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbit are common. So processes similar to the one that formed Neptune in our own Solar System or cold super-Earth may be common in other solar systems.
Categories: astro-ph.EP