NASA scientists hailed the safe passage of Comet 3I/ATLAS as it reached its closest approach to Earth on December 19, passing within 167 million miles—farther than Mars' current distance. Discovered in July 2025 by Chile's ATLAS telescope, the interstellar wanderer captivated astronomers worldwide, providing unprecedented data on extrasolar chemistry.
Designated the third confirmed interstellar object after 'Oumuamua (2017) and Borisov (2019), 3I/ATLAS follows a hyperbolic trajectory, unbound by our sun's gravity. Traveling at 137,000 mph, it originated possibly from the Milky Way's thick disk, potentially over 7 billion years old—older than the solar system. James Webb Space Telescope observations revealed unusual carbon dioxide richness and traces of water ice, vapor, carbon monoxide, and carbonyl sulfide, differing from local comets.
Ground-based telescopes like Gemini North captured its shifting hues from red to green, while XMM-Newton's X-ray scans detected hydrogen and nitrogen gases. The UN's International Asteroid Warning Network monitored its path, affirming no collision risk. At perihelion on October 29—1.36 AU from the sun—it developed a coma and tail, visible to backyard scopes as a bright star.
Amateur astronomer Sam Deen identified pre-discovery images from June 2025, obscured by the Galactic Center. Nordic Optical and Teide Observatory confirmed activity on July 2, earning its "3I" label. Perseverance rover imaged it from Mars, and STEREO spacecraft stacked exposures showing its halo.
