Gemini North Telescope Captures Comet 3I/ATLAS Glowing Green After Its Close Encounter With the Sun

Fresh observations from the Gemini North telescope in Hawai‘i have revealed a striking new look for Comet 3I/ATLAS, the third confirmed interstellar object ever detected passing through our solar system. After disappearing behind the Sun during its closest approach, the comet has reemerged with a faint greenish glow, offering scientists valuable clues about how this rare visitor is responding to solar heating as it heads back into interstellar space.

These new images were captured on 26 November 2025 using the Gemini Multi-Object Spectrograph (GMOS) at Gemini North, located on Maunakea. The observations were conducted shortly after the comet reappeared from behind the Sun, giving astronomers a chance to study how its appearance and chemical activity have changed following intense solar exposure.

A Rare Interstellar Visitor Under Close Watch

Comet 3I/ATLAS holds a special place in astronomy. It is only the third interstellar object ever confirmed to pass through our solar system, following 1I/‘Oumuamua in 2017 and 2I/Borisov in 2019. Unlike typical comets that originate from the Kuiper Belt or Oort Cloud, 3I/ATLAS formed around another star entirely before being ejected into interstellar space and eventually drifting into our cosmic neighborhood.

Because of its rarity, every opportunity to observe 3I/ATLAS is significant. Scientists are especially interested in how its composition compares to comets that formed within our own solar system and how it behaves when exposed to the Sun’s heat.

What Gemini North Saw After the Comet Reappeared

After its solar passage, Comet 3I/ATLAS was spotted near Zaniah, a triple-star system in the constellation Virgo. This timing allowed astronomers to capture images that show how the comet has evolved since it was last visible.

The Gemini North images are composite color images created using four different filters: blue, green, orange, and red. During the observations, the telescope was programmed to track the comet itself, keeping it fixed at the center of the frame. As a result, background stars appear as multicolored streaks, since their positions shifted relative to the comet during the exposures.

This technique makes the comet’s structure and glow stand out clearly against the star-filled background, helping scientists isolate details in its coma, the cloud of gas and dust surrounding its nucleus.

Why the Comet Now Looks Green

One of the most notable changes in the new images is the comet’s greenish hue. Earlier observations of 3I/ATLAS, including images taken at Gemini South in Chile during a previous observing session, showed the comet with a more reddish appearance. The shift in color is not just cosmetic—it reflects real changes in the comet’s chemistry.

The green glow comes primarily from diatomic carbon (C₂), a highly reactive molecule made of two carbon atoms. As the comet warms up near the Sun, ices on and beneath its surface begin to sublimate, releasing gases into the coma. When diatomic carbon is exposed to sunlight, it emits light at green wavelengths, producing the faint glow now seen in the Gemini North images.

This type of green emission is common in comets, but seeing it in an interstellar comet provides an important point of comparison with comets native to our solar system.

Tracking Changes After Perihelion

One of the key scientific goals of these observations is to understand how Comet 3I/ATLAS behaves after perihelion, the point in its orbit closest to the Sun. Heating does not always affect a comet instantly. In many cases, there is a delay as heat slowly penetrates the interior of the nucleus.

This delayed heating can lead to:

• The activation of new chemical reactions
• The release of different gases than those seen earlier
• Sudden outbursts of gas and dust

Astronomers do not yet know whether 3I/ATLAS will experience such changes, but continued monitoring with Gemini and other observatories will help detect any shifts in its activity or composition as it moves farther away from the Sun and begins to cool.

Science and Public Engagement Combined

These observations were not only scientifically valuable but also part of a broader public outreach effort. The data were collected during a Shadow the Scientists observing session, an initiative designed to give students and members of the public a real-time view into how professional astronomers conduct research using some of the world’s most advanced telescopes.

The observing program was led by Bryce Bolin, a research scientist at Eureka Scientific, in collaboration with NSF NOIRLab, which operates the International Gemini Observatory. Gemini North and its twin telescope, Gemini South, are among the most powerful optical and infrared observatories in the world.

By involving learners directly in observing sessions and data collection, programs like Shadow the Scientists aim to demystify astronomy, showing how data are gathered, processed, and analyzed rather than presenting science as a finished product.

Why Interstellar Comets Matter

Interstellar objects like Comet 3I/ATLAS are scientific goldmines. They are natural samples from other planetary systems, offering insights into how planets and comets form around stars beyond the Sun. Unlike spacecraft missions, which require decades of planning and enormous budgets, interstellar visitors deliver themselves to us—briefly, but with enormous scientific potential.

Studying their composition helps astronomers answer questions such as:

• Are the building blocks of planets similar across the galaxy?
• How common are carbon-rich materials in other star systems?
• Do interstellar comets behave differently from solar system comets?

The presence of familiar molecules like diatomic carbon suggests some chemical similarities, but subtle differences could reveal new information about the environments in which these objects formed.

What Happens Next for Comet 3I/ATLAS

Comet 3I/ATLAS is now on its way out of the solar system, following a hyperbolic trajectory that will eventually carry it back into interstellar space. Before it fades from view, astronomers plan to continue observing it to track:

• Changes in its gas composition
• Any signs of outbursts or jet activity
• How quickly its activity declines as it cools

Each new observation adds another piece to the puzzle of how interstellar objects evolve when they pass close to a star like our Sun.

A Brief Look at Gemini North and GMOS

The Gemini North telescope is an 8.1-meter optical and infrared telescope situated at a high-altitude site chosen for its clear skies and stable atmospheric conditions. The Gemini Multi-Object Spectrograph (GMOS) is a versatile instrument capable of both imaging and spectroscopy, making it ideal for studying faint, fast-moving targets like comets.

GMOS allows astronomers to analyze not just how objects look, but also what they are made of, by breaking their light into spectra that reveal chemical signatures.

Why This Observation Matters

The green glow of Comet 3I/ATLAS is more than a visual curiosity. It represents a moment when cutting-edge technology, rare cosmic timing, and public engagement come together to expand our understanding of the universe. As one of only a handful of known interstellar visitors, 3I/ATLAS reminds us that our solar system is not isolated—it is part of a much larger, dynamic galaxy filled with wandering remnants of planet formation.

Research reference:
https://www.gemini.edu/news/press-releases/noirlab2532