Comet 3I/ATLAS displays greenish hue in new Gemini North telescope images

Comet 3I/ATLAS streaks across stars and galaxies in this image captured by the Gemini Multi-Object Spectrograph (GMOS) on Gemini North on Maunakea in Hawai‘i. Credit: NSF NOIRLab

Gemini North captured new images of Comet 3I/ATLAS after it reemerged from behind the sun on its path out of the solar system. The data were collected during a Shadow the Scientists session—a unique outreach initiative that invites students around the world to join researchers as they observe the universe on the world's most advanced telescopes.

Details of the Gemini North observations

On 26 November 2025, scientists used the Gemini Multi-Object Spectrograph (GMOS) on Gemini North at Maunakea in Hawai'i to obtain images of the third-ever detected interstellar object, Comet 3I/ATLAS. The new observations reveal how the comet has changed after making its closest approach to the sun. Gemini North is one half of the International Gemini Observatory and operated by NOIRLab.

After emerging from behind the sun, 3I/ATLAS reappeared in the sky close to Zaniah, a triple-star system located in the constellation Virgo. These observations were taken as part of a public outreach initiative organized by NOIRLab in collaboration with Shadow the Scientists, an initiative created to connect the public with scientists to engage in authentic scientific experiments, such as astronomy observing experiences on world-class telescopes.

The scientific program was led by Bryce Bolin, a research scientist from Eureka Scientific.

A deep image of interstellar Comet 3I/ATLAS captured by the Gemini Multi-Object Spectrograph (GMOS) on Gemini North on Maunakea in Hawai‘i. Credit: NSF NOIRLab

Imaging techniques and comet appearance

This image is composed of exposures taken through four filters—blue, green, orange, and red. As exposures are taken, the comet remains fixed in the center of the telescope's field of view. However, the positions of the background stars change relative to the comet, causing them to appear as colorful streaks in the final image.

In earlier images of the comet, captured during a Shadow the Scientists session hosted at Gemini South in Chile, it appears to have a red hue. However, in the new image released today, it appears to have a faint greenish glow.

This is due to light emitted by gases in the comet's coma that are evaporating as the comet heats up, including diatomic carbon (C2), a highly reactive molecule of two carbon atoms that emits light at green wavelengths.

Future monitoring and public engagement

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.

A delay can activate the evaporation of new chemicals or trigger a comet outburst. Gemini will continue to monitor the comet as it leaves the solar system and detect changes in its gas composition and outburst behavior.

This collaboration with Shadow the Scientists builds on NOIRLab's tradition of combining cutting-edge science with public engagement, ensuring that remarkable cosmic events are shared as widely as possible. By involving learners directly in observing sessions and data collection, programs like this one not only advance knowledge but also inspire the next generation of explorers.

"Sharing an observing experience in some of the best conditions available gives the public a truly front-row view of our interstellar visitor," says Bolin. "Allowing the public to see what we do as astronomers and how we do it also helps demystify the scientific and data collection process, adding transparency to our study of this fascinating object."

Citation: Comet 3I/ATLAS displays greenish hue in new Gemini North telescope images (2025, December 12) retrieved 12 December 2025 from https://phys.org/news/2025-12-gemini-north-images-reveal-greenish.html

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