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Interstellar Comet 3I/ATLAS Brightens Sharply and Shows Unexplained Acceleration Ahead of Dec. 19 Flyby

Major telescopes are queued to probe its makeup with dedicated observations in December.

Overview

  • MPC and NASA JPL reports note a roughly fivefold increase in visible-band brightness and a measurable non‑gravitational acceleration, raising new questions about the object's behavior.
  • Preliminary imaging has not revealed the massive gas coma expected if strong outgassing drove the acceleration, a key test scientists plan to pursue with December observations.
  • The comet’s closest approach is set for December 19 at about 270 million kilometers from Earth, offering a rare window for detailed study.
  • NASA’s Planetary Defense office reiterates there is no impact risk from 3I/ATLAS during its passage through the inner solar system.
  • Spectra from Hubble and ESA indicate vapor-phase nickel, water, and previously unreported compounds, underscoring an unusual composition that will be targeted by Webb, Hubble, TESS, Swift, SPHEREx, and a NASA analysis campaign beginning December 29.