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Astronomers Weigh First Free-Floating Planet Using Gaia–Earth Parallax

The result validates a technique that upcoming Roman surveys could use to build a robust census of rogue worlds.

Overview

  • Published in Science on January 1, 2026, the study reports the first simultaneous mass and distance measurement for a rogue planet.
  • The object, designated KMT-2024-BLG-0792 / OGLE-2024-BLG-0516, is about 22% of Jupiter’s mass and lies roughly 9,785 light-years away near the Galactic center.
  • Ground networks (KMTNet and OGLE) and ESA’s Gaia observed the May 3, 2024 microlensing event from separated vantage points, with Gaia’s view offset by about two hours.
  • Microlens parallax from the Earth–Gaia baseline broke the longstanding mass–distance degeneracy, confirming a Saturn-mass free-floating planet.
  • The planet’s mass favors an origin in a planetary system followed by ejection, and researchers expect NASA’s Roman Telescope, planned for 2027, to enable many more such measurements.