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Astronomers Pin Down Mass and Distance of a Rogue Planet for the First Time

Simultaneous Earth–Gaia microlensing measurements reveal a Saturn‑mass wanderer nearly 10,000 light‑years away, validating a technique poised to map such worlds with Roman.

Overview

  • The finding appears in Science on January 1, 2026, marking the first simultaneous mass and distance determination for a free‑floating planet.
  • Analysis places the object at roughly 9,785 light‑years toward the Galactic bulge with a mass about 22% that of Jupiter, comparable to Saturn.
  • KMTNet and OGLE recorded the event from Earth while ESA’s Gaia at L2 saw the peak about two hours later, enabling a parallax measurement that broke the mass–distance degeneracy.
  • Designated KMT-2024-BLG-0792 (also OGLE-2024-BLG-0516), the lens sits in the so‑called “Einstein desert,” a sparsely sampled regime between low‑mass and super‑Jupiter lenses.
  • Researchers argue the Saturn‑like mass favors an origin within a planetary system followed by ejection, and say the validated method should scale with NASA’s Nancy Grace Roman Space Telescope planned for 2027.