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The rare and mysterious interstellar comet 3I/ATLAS got brighter and greener as it approaches Earth on December 19. The recent images captured by the Gemini North telescope reveal that the interstellar comet 3I/ATLAS reveal that the comet 3I/ATLAS taken on a striking green hue and is growing brighter as it comes near to our planet, Live Science reported. This transformation has been attributed to the vaporization of ice and dust after its close solar approach. The comet is currently passing through our solar system and will be at its closest point to Earth on December 19 as it will come within 170 million miles (270 million kilometres) of our planet.
The interstellar comet was discovered on July 1, 2025, by the ATLAS telescope in Chile. It is the third interstellar object ever detected, following 1I/’Oumuamua and 2I/Borisov. 3I/ATLAS is believed to be the largest and oldest interstellar object observed so far, offering scientists a unique opportunity to study material formed around another star.
Why interstellar comet glows green
Astronomers have captured stunning new images which shows that the interstellar comet 3I/ATLAS is not only brightening but also taking on a distinct green hue as it approaches Earth. Once noticeably redder, the comet now emits a faint greenish glow, indicating the release of fresh molecules into space, according to a photo release by NOIRLab. The comet 3I/ATLAS offers a rare chance to study the composition, behaviour, and origins of objects from beyond our solar system.
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The latest image of the comet was captured by scientists using the Gemini Multi-Object Spectrograph (GMOS) on the 8.1-meter telescope Gemini North telescope atop Hawaii’s dormant Mauna Kea volcano on November 26, 2025, four weeks after its perihelion. After its closest approach to the Sun, the comet is now emitting tonnes of dust and forming a bright coma, along with a tail. To capture the same, scientists observed it using four filters – blue, red, orange and green. They found that gas in the coma now emits a faint greenish hue, which also happened a few weeks ago.
What is the reason behind the colour change?
The green colour of the comet is caused by diatomic carbon (C2) molecules in its coma, which emit light at green wavelengths when exposed to solar radiation. It offers a rare glimpse into the composition and behaviour of objects found beyond our solar system. This phenomenon is not uncommon in comets, but the recent change in 3I/ATLAS’s colour from red to green suggests that new molecules are being released as it heats up.
“What remains unknown is how the comet will behave as it leaves the Sun’s vicinity and cools down. Many comets have a delayed reaction in experiencing the Sun’s heat due to the lag in time that it takes for heat to make its way through the interior of the comet,” the scientists wrote in a statement.
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Astronomers expect 3I/ATLAS to brighten further or undergo fresh outbursts as it approaches its closest point to Earth—about 270 million kilometres—on December 19. Scientists say comets often respond slowly to solar heating, which can trigger new jets of gas and dust over time. Continued observations are expected to shed new light on cometary behaviour and the physical processes governing interstellar objects. Believed to be
