Live observations on the program Shadow the Scientists show a change in the comet's color after its close approach to the sun, likely due to gases in the comet emitting green light.
Gemini North has captured new images of interstellar comet 3I/ATLAS after it reappeared after passing behind the Sun on its way out of the solar system. The data was collected during Shadow the Scientists — a unique outreach initiative that invites students from around the world to join researchers as they observe the universe through the world’s most advanced telescopes.
On November 26, 2025, scientists used the Gemini North GMOS instrument on Mauna Kea, Hawaii, to image the third interstellar object ever detected, interstellar comet 3I/ATLAS. The new observations show how the comet changed after its closest approach to the Sun. Gemini North is one of two telescopes in the International Gemini Observatory, which is funded in part by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab.
After re-emerging from behind the Sun, 3I/ATLAS was visible in the sky near Zaniah, a triple star system in the constellation Virgo. The observations were made as part of a public outreach initiative organized by NSF NOIRLab, in partnership with Shadow the Scientists — an initiative designed to connect the public with scientists and participate in real-world science experiments, such as astronomical observing experiences with world-class telescopes [1]. The science program was led by Bryce Bolin, a researcher at Eureka Scientific.
The image is made up of exposures through four filters—blue, green, orange, and red. While the exposures are taken, the comet remains fixed in the center of the telescope's field of view. In contrast, the position of the background stars changes relative to the comet, so they appear in the final image as colored bands.
In earlier images of the comet, taken during the Shadow the Scientists meeting at Gemini South in Chile, it appeared reddish in color. But in the new image released today, it appears to have a faint greenish glow. This is due to light emitted from gases in the comet’s “cemetery”—the cloud of gas and dust surrounding the comet’s nucleus—that evaporate as the comet heats up. Among these gases is carbon diatomic (C2), a highly reactive molecule made up of two carbon atoms that emits light at green wavelengths.
It is not yet known how the comet will behave as it moves away from the Sun and cools. Many comets have a delayed response to solar heating, due to the time it takes for the heat to penetrate the comet. Such a delay could trigger the evaporation of new chemicals or ignite a cometary eruption. Gemini will continue to follow interstellar comet 3I/ATLAS as it leaves the solar system, looking for changes in its gas composition and eruption patterns.
The collaboration with Shadow the Scientists builds on NOIRLab’s tradition of combining cutting-edge science with public engagement to bring extraordinary cosmic events to the widest possible audience. By engaging participants in hands-on observation sessions and data collection [2], such programs not only advance knowledge, but also inspire the next generation of researchers and discoverers.
“Sharing an observing experience under the best possible conditions gives the public a front-row seat to our interstellar guest,” says Bolin. “Allowing the public to see what we do as astronomers and how we do it also helps demystify the science and data collection process, adding transparency to our research on this fascinating object.”
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