I watched scientists observe the interstellar comet 3I/ATLAS in real time. This is what they saw.

The Gemini South telescope shows interstellar comet 3I/ATLAS as a large, bright source of light at the center of the telescope. (Image credit: NOIRLab/Gemini South Observatory/Shadow the Scientists)

Few cosmic visitors have captivated astronomers as much as interstellar comet 3I/ATLAS. This icy wanderer, hurtling through our solar system from the depths of interstellar space, is only the third such object known, and its origin remains a mystery.

Since its discovery on July 1, 2025, by the Deep Random Survey telescope in Chile, part of the ATLAS (Asteroid Terrestrial-impact Last Alert System) project, scientists have been rushing to point telescopes at the comet, as experts and the public alike are eager to get a closer look. Even NASA's Hubble and James Webb space telescopes recently caught a glimpse of the icy comet as it continues its journey toward our Sun.

So when I learned that Gemini South in Chile was hosting a live webcast as part of the Shadow of Scientists (StS) initiative, which aims to bring real-time research to the public, I knew I had to join in. As the livestream began, I and other participants found themselves in the Gemini South instrument room, where astronomers began calibrating the telescope. The team planned to use the Gemini Multi-Object Spectrographs (GMOS) and the new Gemini High-resolution Optical Spectrograph (GHOST) to measure the chemical abundance of 3I/ATLAS.

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NASA's first observations have shown that Comet 3I/ATLAS is unusually “active.”

Astronomer Karen Mech of the University of Hawaii's Institute for Astronomy reminded the audience how rare such opportunities are: “Interstellar objects are the building blocks of other solar systems that have been completely ejected from their host star by chance and have flown past ours. Whenever you see one of these objects — and we've only had three — everyone wants to use as much telescope time as possible to figure out whether they're similar or different from bodies in our solar system.”

Other experts echoed Mech's sentiments, saying they had to ask the director of the Gemini South Observatory to make time available for other observers to hold the event. A recording of the event can be viewed at the link below.

While Mitch set the stage, the telescope team in Chile was preparing the giant 26-foot (8-meter) mirror for the painstaking work. In the control room, science operations specialists walked us through the process: “We’re calibrating, setting up the telescope, and checking the sky conditions… It’s very dry tonight, steady winds, perfect for good seeing.”

The comet caught my attention because it had snowed in the area recently. While the Gemini South observatory was not as badly affected by the fallout, its neighbor below, the Atacama Large Millimeter/submillimeter Array (ALMA) on Chajnantor, was so covered in snow that all scientific work was temporarily suspended. Fortunately, the snow had melted by the time of the live broadcast, allowing everything to proceed as smoothly as possible.

As the calibrations continued for an hour, Mech answered questions and kept the audience intrigued about the moment when the comet might be seen: “We just don’t know what we’re going to see tonight, and that’s exciting.”

Before Gemini South began observing, both the Hubble Space Telescope and the JWST had already conducted preliminary studies. Hubble estimated the comet’s nucleus to be less than 3 kilometers in diameter, hidden by a halo of dust and gas. Meanwhile, the JWST had difficulty seeing the nucleus through the halo, revealing that 3I/ATLAS appears to be unusually rich in carbon dioxide. This distinguishes it from its predecessor 2I/Borisov, the second interstellar comet ever discovered, which had much more carbon dioxide.

Mech and other Gemini South mission members hoped to confirm that 3I/ATLAS does indeed contain large amounts of carbon dioxide, or dry ice, that will burn up as it approaches the Sun. Mech explained that the comet will make its closest approach to the Sun in October, but will be impossible to detect because it will be moving behind the Sun at that time. She mentioned that NASA scientists are currently discussing the possibility of temporarily repurposing existing spacecraft to observe 3I/ATLAS from the other side of the Sun, which would eliminate this blind spot.

Even if that doesn't happen, observations could resume in November, when Comet 3I/ATLAS re-emerges from behind the Sun. Depending on its activity and chemical makeup, the comet could brighten even more, burning up more gas and dust. But even if 3I/ATLAS does brighten, scientists will still have limited time to study it.

“Once these objects get too dim, you never see them again,” Mech said. “They just pass through our solar system. Even 1I/'Oumuamua is still within our system. It's in the Kuiper Belt right now.”

“Oumuamua is the first interstellar object ever seen in our solar system. Astronomers discovered it back in 2017.”

As the telescope began to swivel toward 3I/ATLAS, the experts paused, watching the scientists' shared screen in the Gemini South control center. Mech had previously explained that the first chemical they hoped to see with GMOS was cyanide interacting with sunlight.

Then the first image appeared, a bright, blurry spot. We all gasped when we saw it, and the discussion of the event was full of surprise and delight.

“You’re looking at a brick in someone else’s house,” Mitch said. But, she added, “it’s impossible to track a comet by its trajectory because everything else is moving around it.”

The first images showed a faint but distant glow from a developing tail, confirming that this visitor was behaving more like a “classic” comet than the strange, elongated 'Oumuamua that Meech had also studied.

“This is a raw image,” she said. “I'm sure with further calibration it will have a longer tail.”