Gemini North has obtained new color images of Comet 3I/ATLAS after the interstellar object emerged from behind the Sun on its outbound trajectory from the Solar System. Using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope at Maunakea in Hawaii, scientists observed the comet on 26 November 2025 to study how it has evolved since perihelion.
The observations were co Tucson AZ (SPX) Dec 16, 2025
Gemini North has obtained new color images of Comet 3I/ATLAS after the interstellar object emerged from behind the Sun on its outbound trajectory from the Solar System. Using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope at Maunakea in Hawaii, scientists observed the comet on 26 November 2025 to study how it has evolved since perihelion.
The observations were conducted as part of a Shadow the Scientists session, an outreach program that connects students and the public with astronomers during live observing runs on major telescopes, and the scientific program was led by Bryce Bolin of Eureka Scientific.
In the new Gemini North images, the comet displays a faint greenish glow that contrasts with earlier Shadow the Scientists observations from Gemini South in Chile, where the object appeared more red. The composite image combines exposures taken through four filters - blue, green, orange, and red - while the telescope tracks the comet, causing background stars to appear as multicolored streaks as they move across the field during the observations.
The green tint arises from emission by gases in the comet's coma that are released as solar heating drives sublimation, including diatomic carbon (C2), a reactive molecule consisting of two carbon atoms that radiates strongly at green wavelengths.
Researchers now aim to follow how 3I/ATLAS changes as it recedes from the Sun and cools. Many comets respond to solar heating with a delay because it takes time for heat to propagate into their interiors, which can later initiate the evaporation of new volatile species or trigger outbursts as trapped material escapes. Continued monitoring with Gemini will track shifts in the comet's gas composition and any outburst activity as this third-known interstellar object travels back into interstellar space.
The Shadow the Scientists collaboration with NSF NOIRLab is designed to merge front-line astronomical observing with direct public participation. By involving learners in real-time observing sessions and making the resulting data available through the Gemini Archive, the program provides access to authentic research material while highlighting notable events such as the passage of 3I/ATLAS.
"Sharing an observing experience in some of the best conditions available gives the public a truly front-row view of our interstellar visitor," Bolin said, adding that opening the observing process to the public helps demystify how astronomers collect and analyze data on targets like this comet.
"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."
Related Links
NSF NOIRLab
Stellar Chemistry, The Universe And All Within It