We present the gravitational microlensing discovery of a 4 M_Uranus planet
that orbits a 0.7 M_Sun star at ~18 AU. This is the first known analog of
Uranus. Similar planets, i.e., cold ice-giants, are inaccessible to either
radial velocity or transit methods because of the long orbital periods, while
low reflected light prevents direct imaging. We discuss how similar planets may
contaminate the sample of the very short microlensing events that are
interpreted as free-floating planets with an estimated rate of 1.8 per main
sequence star. Moreover, the host star has a nearby stellar (or brown dwarf)
companion. The projected separation of the planet is only ~3 times smaller than
that of the companion star, suggesting significant dynamical interactions.Comment: published in ApJ; the photometry and the code used for fitting the
double-lens extended-source (with limb darkening) microlensing model are
attached as ancillary file
