Comet 3I/ATLAS streaks across a dense star field in this image captured by the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope at Cerro Pachón in Chile. This image is composed of exposures taken through 4 filters: red, green, blue and ultraviolet. 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. Image via International Gemini Observatory/ NOIRLab/ NSF/ AURA/ Shadow the Scientist. Image processing via J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab)/ T.A. Rector (University of Alaska Anchorage/NSF NOIRLab)/ M. Zamani (NSF NOIRLab). Used with permission.
Astronomers captured these images of the famous interstellar object 3I/ATLAS live from the Gemini South telescope control room in Chile during Shadow the Scientists program in August, 2025. NOIRLab published this story on September 4. Edits by EarthSky.
3I/ATLAS shows a comet tail
On August 27. 2025, researchers used the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope at Cerro Pachón in Chile to obtain deep, multi-color images of interstellar comet Comet 3I/ATLAS.
These observations were taken as part of a public outreach initiative organized by NSF NOIRLab in collaboration with Shadow the Scientists. The program is 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 Karen Meech, astronomer at the University of Hawai‘i Institute for Astronomy.
In the images captured during the session, the comet displays a broad coma, a cloud of gas and dust that forms around the comet’s icy nucleus as it gets closer to the sun. And it displays a tail spanning about 1/120th degree in the sky (where 1 degree is about the width of a pinky finger on an outstretched arm) and pointing away from the sun. These features are significantly more extended than they appeared in earlier images of the comet, showing that 3I/ATLAS has become more active as it travels through the inner solar system.
Shadow the Scientists program
Members of the public, including students from Hawai‘i and La Serena, Chile, were invited to remotely join the Gemini South control room. During a special two-hour Zoom session, they could interact directly with astronomers, ask questions about interstellar cometary science, and follow the progress of the observations in real time. The event was followed across the world with people joining from Europe, New Zealand, and South America.
More than just capturing stunning images, the main scientific motivation of the observing session was to collect the comet’s spectrum, which refers to the wavelengths of light that it emits. A spectrum can give scientists information about the comet’s composition and chemistry, which enables them to understand how the comet changes as it passes through our solar system.
The interstellar object was first detected on July 1, 2025, by ATLAS (Asteroid Terrestrial-impact Last Alert System). The new observations suggest that the dust and ice of 3I/ATLAS are broadly similar to those of comets native to our solar system, hinting at shared processes in the formation of planetary systems around other stars.
During the observing session, Bin Yang, assistant professor at the Instituto de Estudios Astrofísicos (IEA) at Universidad Diego Portales, guided participants through the interpretation of the spectral data, while Meech led a discussion about the importance of interstellar objects for understanding the formation and evolution of planetary systems. Meech said:
The primary objectives of the observations were to look at the colors of the comet, which provide clues to the composition and sizes of the dust particles in the coma, and to take spectra for a direct measure of the chemistry. We were excited to see the growth of the tail, suggesting a change in the particles from the previous Gemini images, and we got our first glimpse of the chemistry from the spectrum.
3I/ATLAS is a rare object
Interstellar comets are extraordinarily rare: 3I/ATLAS is only the 3rd confirmed example after Comet 1I/’Oumuamua in 2017 and Comet 2I/Borisov in 2019. Unlike comets bound to our sun, 3I/ATLAS is traveling on a hyperbolic orbit that will eventually carry it back into interstellar space. Its brief passage through our solar system gives astronomers a once-in-a-lifetime opportunity to study material that formed around a distant star.
This effort 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. Meech explained:
As 3I/ATLAS speeds back into the depths of interstellar space, this image is both a scientific milestone and a source of wonder. It reminds us that our solar system is just one part of a vast and dynamic galaxy, and that even the most fleeting visitors can leave a lasting impact.
Plans for future observations
Also present during the observing session and lending his scientific expertise was Bryce Bolin, research scientist from Eureka Scientific. He said:
These observations provide both a breathtaking view and critical scientific data. Every interstellar comet is a messenger from another star system, and by studying their light and color, we can begin to understand the diversity of worlds beyond our own.
In November 2025, when Comet 3I/ATLAS reemerges from behind the sun, Bolin will host a follow-up Shadow the Scientists observing session, this time bringing the public into the control room of the Gemini North telescope in Hawai‘i.
Gemini South is 1/2 of the International Gemini Observatory, partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab.
A deep image of interstellar Comet 3I/ATLAS captured by the Gemini Multi-Object Spectrograph (GMOS) on Gemini South at Cerro Pachón in Chile. The image shows the comet’s broad coma – a cloud of gas and dust that forms around the comet’s icy nucleus as it gets closer to the sun – and a tail spanning about 1/120th degree in the sky and pointing away from the sun. 3I/ATLAS is only the 3rd confirmed interstellar visitor to our solar system. Image via International Gemini Observatory/ NOIRLab/ NSF/ AURA/ Shadow the Scientist. Image processing via J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab)/ T.A. Rector (University of Alaska Anchorage/NSF NOIRLab)/ M. Zamani (NSF NOIRLab). Used with permission.
Bottom line: Astronomers captured live images of comet 3I/ATLAS from the Gemini South telescope control room in Chile. The images showed a tail for the comet.
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