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Interstellar Comet 3I/ATLAS Reappears After Sun Swing as Observatories Confirm Water Outgassing

Researchers are mobilizing major observatories to explain its unusual blue color with confirmed water outgassing.

Overview

  • New post‑perihelion images captured from Oct. 31 to early November, including by Qicheng Zhang at Lowell Observatory, show the comet’s unexpectedly blue appearance and renewed brightness.
  • NASA’s Neil Gehrels Swift Observatory detected hydroxyl emission, a proxy for water, indicating active outgassing at unusually large distances from the Sun.
  • NASA and ESA report a hyperbolic, high‑speed trajectory of over roughly 210,000 km/h with no impact risk, with the closest Earth approach expected around Dec. 19 at about 270 million kilometers.
  • Hubble, Swift and ESA’s JUICE are conducting coordinated observations through November to study composition and activity, while estimates of nucleus size remain wide, from hundreds of meters to several kilometers.
  • Claims that the object could be artificial remain disputed by most researchers, as agencies describe behavior consistent with a natural comet.