HomeScienceComet 3I/ATLAS brightens and turns greener as Earth encounter approaches

Comet 3I/ATLAS brightens and turns greener as Earth encounter approaches

New telescope images show interstellar comet 3I/ATLAS brightening and turning green after solar heating, raising questions about its chemistry and whether surprising outbursts may appear as it nears Earth soon.

December 13, 2025 / 15:02 IST
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Comet 3I/ATLAS Turns Greener and Brighter as Earth Encounter Nears (Image: Gemini North / NSF NOIRLab))
Comet 3I/ATLAS Turns Greener and Brighter as Earth Encounter Nears (Image: Gemini North / NSF NOIRLab))

New telescope images reveal interstellar comet 3I/ATLAS intensifying rapidly. The images show the object growing brighter and greener recently. Scientists say the change follows its close solar passage. The observations focus on activity ahead of Earth’s upcoming flyby.

The images were taken on 26/11/2025 using Gemini North. The telescope is located atop Hawaii’s dormant Mauna Kea volcano. Researchers observed the comet during one of its active phases. Heating from intense sunlight is driving major surface changes. Ice is sublimating and releasing dust into surrounding space. This process forms a glowing coma and extended tail.

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3I/ATLAS comet: What is happening now
To capture the images, astronomers used four observation filters. These included blue, red, orange, and green wavelengths. The comet’s coma now emits a faint green glow. This colour was absent during observations several months earlier. According to NOIRLab, diatomic carbon causes the green light. The molecule emits green when excited by sunlight. NOIRLab operates the Gemini telescopes in Hawaii and Chile.

Many solar system comets show similar green colouring. Examples include comet 12P Pons-Brooks and C/2025 F2. However, earlier images showed 3I/ATLAS appearing distinctly redder. Gemini South captured those observations during late August. Scientists say this suggests new molecules are emerging. The colour change offers clues to internal composition.