Overview

• JWST observed 3I/ATLAS with NIRSpec on Aug. 6, and an Aug. 25 preprint reports a carbon dioxide–dominated coma with one of the highest CO2/H2O ratios seen in a comet.
• SPHEREx and other observatories are gathering complementary infrared data as coordinated campaigns refine the comet’s composition, activity, and basic properties.
• The reported chemistry may point to formation near the CO2 ice line in a parent disk or to ices altered by higher radiation exposure, though the interpretation remains preliminary.
• 3I/ATLAS is the third confirmed interstellar visitor, traveling on a hyperbolic path at over 130,000 mph, with perihelion expected in late October and visibility declining as it moves behind the sun later in the fall.
• Size estimates remain unsettled, with Hubble suggesting a nucleus no larger than about 3.5 miles across, and expert consensus dismisses separate speculative claims of artificial origin.