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Space–Ground Observations Pin Down Mass of a Rogue Planet

A parallax signal across Earth–Gaia baselines broke the microlensing degeneracy, indicating a Saturn-mass world roughly 3,000 parsecs distant.

Overview

  • The Science report finds a mass near 22% of Jupiter and a location about 3,000 parsecs from the Milky Way’s center.
  • Astronomers observed a hours-long microlensing event simultaneously from Gaia at L2 and multiple ground surveys, enabling a measurable parallax.
  • Combining parallax with finite-source point-lens modeling yielded direct mass and distance estimates, a rarity for free-floating planets.
  • Follow-up imaging detected no light from a host, supporting the classification as an unbound planet likely ejected from a planetary system.
  • Some coverage cites an Earth-mass estimate from alternative modeling, underscoring uncertainties that future coordinated surveys, including NASA’s Roman telescope, aim to reduce.