A bold truth about interstellar visitors: Comet 3I/ATLAS is brightening and turning greener as it nears Earth, and new imagery confirms the change. The latest telescope photos show the comet more active than it has been since it swung close to the Sun in late October, hinting at possible fresh, vivid outbursts as its Earth approach tightens next week.
Captured on November 26 with the Gemini North telescope atop Hawaii’s Mauna Kea, these images freeze 3I/ATLAS during one of its peak activity phases. Solar heating has melted surface ice, driving off gas and dust that expand into a glowing coma around the nucleus and a long, radiant tail trailing behind.
Why does 3I/ATLAS look green?
Don’t rush to blame extraterrestrial origins for the hue. The comet is releasing diatomic carbon (C2), a molecule that glows green when excited by solar radiation. The NOIRLab, which operates Gemini North and its Chilean twin Gemini South, notes this Green glow arises from the C2 emissions as the comet’s material vents into space. This green coloration is common among actively heated comets in our Solar System.
Past comparisons include last year’s green “Mother of Dragons” comet 12P/Pons-Brooks and the recently spotted Comet C/2025 F2 (SWAN), both known for their vivid green tails when active near the Sun.
Interestingly, Gemini South initially recorded 3I/ATLAS as redder in late August, months before its solar flyby, suggesting the comet is releasing new molecules as it heats—clues about its mysterious interior and composition.
Could another outburst be on the horizon?
As 3I/ATLAS heads toward its closest approach to Earth on December 19, coming within roughly 170 million miles (about 270 million kilometers), observers anticipate further surprises. NOIRLab notes that how the comet behaves after leaving the Sun’s vicinity remains uncertain. Many comets respond to solar heating with delays: heat propagates inward, and the resulting lag can trigger new molecule release or even an outburst as the interior finally responds.
3I/ATLAS is the third confirmed interstellar visitor, following 1I/’Oumuamua and 2I/Borisov. It was detected in late June, racing through our solar system at about 130,000 mph (210,000 km/h) on a hyperbolic trajectory that will not bring it back through our neighborhood.
Broad context and current insights
Observatories and spacecraft around the Solar System continue to monitor 3I/ATLAS to refine our understanding of its size, trajectory, composition, and origins. Studying this object in depth could illuminate details about the frontier of our galaxy and the earliest star systems in the Milky Way.
Note on the author
Brandon, Live Science’s space and physics editor, brings more than two decades of editorial experience and has contributed to major outlets. His work often explores black holes, asteroids, comets, and the search for life beyond Earth.
