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A free-floating-planet microlensing event caused by a Saturn-mass object

2025/12/31 by Subo Dong, Zexuan Wu, Yoon-Hyun Ryu +39 · 2 voices
Physics and Astronomy · #astro-ph.EP #astro-ph.GA #astro-ph.SR

paper · pdf · doi:10.1126/science.adv9266

Abstract

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.

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