A population of free-floating planets is known from gravitational microlensing surveys. None have a directly measured mass, owing to a degeneracy with the distance, but the population statistics indicate that many are less massive than Jupiter. We report a microlensing event -- KMT-2024-BLG-0792/OGLE-2024-BLG-0516, which was observed from both ground- and space-based telescopes -- that breaks the mass-distance degeneracy. The event was caused by an object with 0.219^{+0.075}_{-0.046} Jupiter masses that is either gravitationally unbound or on a very wide orbit. Through comparison with the statistical properties of other observed microlensing events and predictions from simulations, we infer that this object likely formed in a protoplanetary disk (like a planet), not in isolation (like a brown dwarf), and dynamical processes then ejected it from its birth place, producing a free-floating object.
@article{arxiv.2601.00057,
title = {A free-floating-planet microlensing event caused by a Saturn-mass object},
author = {Subo Dong and Zexuan Wu and Yoon-Hyun Ryu and Andrzej Udalski and Przemek Mroz and Krzysztof A. Rybicki and Simon T. Hodgkin and Lukasz Wyrzykowski and Laurent Eyer and Thomas Bensby and Ping Chen and Sharon X. Wang and Andrew Gould and Hongjing Yang and Michael D. Albrow and Sun-Ju Chung and Cheongho Han and Kyu-Ha Hwang and Youn Kil Jung and In-Gu Shin and Yossi Shvartzvald and Jennifer C. Yee and Weicheng Zang and Dong-Jin Kim and Chung-Uk Lee and Byeong-Gon Park and Radoslaw Poleski and Jan Skowron and Michal K. Szymanski and Igor Soszynski and Pawel Pietrukowicz and Szymon Kozlowski and Dorota M. Skowron and Krzysztof Ulaczyk and Mariusz Gromadzki and Milena Ratajczak and Patryk Iwanek and Marcin Wrona and Mateusz J. Mroz and Guy Rixon and Diana L. Harrison and Elme Breedt},
journal= {arXiv preprint arXiv:2601.00057},
year = {2026}
}
Comments
Published in Science. This is the authors' version. See the ancillary file for an animation associated with Fig. 2