Interstellar Comet 3I/ATLAS Shrouded in CO₂ Fog – NASA’s SPHEREx Reveals a Cosmic Visitor’s Secrets
3I/ATLAS (C/2025 N1 ATLAS) was discovered July 1, 2025 by the ATLAS survey telescope in Chile and is on a hyperbolic, unbound path with eccentricity ~6.2, making it the third confirmed interstellar object after 1I/‘Oumuamua and 2I/Borisov. Early estimates suggested a diameter of several kilometers, and Hubble data later indicated a nucleus of about 5–6 km across, making 3I/ATLAS the largest interstellar object observed. SPHEREx detected a huge CO₂ cloud around 3I/ATLAS, with the coma extending at least 348,000 km from the nucleus, alongside evidence of water ice in the nucleus. JWST measurements found a CO₂-to-H₂O ratio of roughly 8:1
