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2w ago

Hubble Confirms 3I/ATLAS as Active Interstellar Comet, Refines Its Size and Speed

Mid-August imaging delivers refined nucleus size with dust-loss measurements ahead of the comet’s October perihelion behind the Sun

Image
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
Interstellar Object 3I/ATLAS Seen in Stunning New Hubble Image

Overview

  • Hubble’s new analyses confirm 3I/ATLAS as an active comet traveling at about 209,000 km/h, making it the fastest interstellar object ever recorded.
  • Observations constrain its nucleus diameter between roughly 320 meters and 5.6 kilometers, narrowing earlier size estimates.
  • Measured dust-emission rates of approximately 6 to 60 kg per second reveal a sunward plume visible at 3.8 AU from the Sun.
  • International teams are coordinating multi-wavelength follow-up with JWST, TESS, Swift and ground-based telescopes through September.
  • Minority artificial-origin theories and unapproved mission studies, such as a Juno Oberth maneuver, remain under review but face significant technical and budget hurdles.