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2w ago

Hubble Refines Size and Confirms Cometary Plume on Fastest Interstellar Object

Observatories worldwide are coordinating multiwavelength campaigns ahead of the object’s closest approach inside Mars’s orbit in late October

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This image of interstellar comet 3I/ATLAS was captured by the Hubble Space Telescope's Wide Field Camera on July 21, 2025. Credit: NASA/ESA/UCLA/STScI
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Overview

  • Hubble observations released Aug. 12 have constrained 3I/ATLAS’s nucleus to between 320 meters and 5.6 kilometers and revealed a sunward dust plume with a faint tail.
  • Measurements verify that 3I/ATLAS is traveling at about 209,000 km/h (130,000 mph), marking it as the fastest interstellar visitor recorded.
  • As only the third confirmed interstellar object after ʻOumuamua and Borisov, 3I/ATLAS is estimated to be roughly eight billion years old and composed of ice, frozen gases and dust.
  • International facilities including JWST, TESS, Swift, the Rubin Observatory and ground-based telescopes are set to gather data across multiple wavelengths as the comet nears perihelion around Oct. 29–30.
  • Spacecraft retarget proposals such as a Juno flyby remain under review, and a minority hypothesis of artificial origin continues to be challenged by most researchers.