Triple Microlens OGLE-2008-BLG-092L: Binary Stellar System with a Circumprimary Uranus-type Planet

TL;DR

This paper reports the discovery of a Uranus-like planet orbiting a star via gravitational microlensing, highlighting its significance as the first such analog and discussing implications for planetary detection and dynamics.

Contribution

It presents the first microlensing detection of a Uranus-mass planet orbiting a star, expanding the known types of exoplanets accessible through this method.

Findings

Discovered a 4 Earth-mass Uranus-like planet at ~18 AU from its star.

Identified a binary stellar system with a potential brown dwarf companion.

Discussed how such planets may influence the interpretation of short microlensing events.

Abstract

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.