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3I/ATLAS Reappears After Solar Pass With Striking Blue Hue and Fresh Activity

Scientists are ramping up a coordinated observing campaign ahead of its safe December 19 flyby at about 270 million kilometers from Earth.

Overview

  • Post-perihelion images captured by astronomer Qicheng Zhang with the Lowell Discovery Telescope and a small personal reflector confirm the interstellar object's return and increased brightness.
  • NASA-affiliated observers using the Neil Gehrels Swift Observatory report ultraviolet hydroxyl emissions that trace water, indicating unusual activity far from the Sun at an estimated tens of kilograms per second.
  • China’s Tianwen-1 orbiter imaged 3I/ATLAS from roughly 30 million kilometers away, returning high-resolution pictures and an animation of its motion, according to the CNSA.
  • Hubble observations set an upper limit of about 5.6 kilometers for the nucleus diameter, though some outlets cite larger 10–30 kilometer estimates, underscoring ongoing uncertainty about its size.
  • On a hyperbolic path exceeding 210,000 km/h and showing atypical features such as a blue-dominated appearance, a reported sunward tail, and post-perihelion brightening, the object remains a target for intensive, multi-mission study.