Few cosmic visitors have captured the fascination of astronomers quite like the interstellar comet 3I/ATLAS. Hurtling through our solar system from the depths of interstellar space, this icy wanderer is only the third known object of its kind, and where it came from remains a mystery.
Since its discovery on July 1, 2025, by the Deep Random Survey remote telescope in Chile, part of the ATLAS (Asteroid Terrestrial-impact Last Alert System) project, scientists have raced to point telescopes toward the visitor as experts and the public are eager for a closer look. Even NASA’s Hubble Space Telescope and the James Webb Space Telescope recently caught glimpses of this icy comet as it continues moving toward our sun.
So, when I heard that the Gemini South Observatory in Chile was hosting a live webcast event — as part of the Shadow the Scientists (StS) initiative, which works to bring the public into the fold of real-time research — I knew I had to join. From the moment the livestream session began, I and other participants were thrown into the control room at Gemini South as astronomers began calibrating the telescope. The team planned to use the GMOS (Gemini Multi-Object Spectrographs) as well as the new Gemini High-resolution Optical SpecTrograph (GHOST) instrument to measure the chemical composition of 3I/ATLAS.
Astronomer Karen Meech from the Institute for Astronomy of the University of Hawai’i reminded the audience just how rare opportunities like this are: “Interstellar objects are building blocks of other solar systems that got kicked completely out of their home star just by chance passing through ours. Whenever you get one of these — and we’ve only had three — everyone wants to use as much telescope time as possible to see if they’re similar or different to the bodies in our solar system.”
Other experts added to Meech’s point, saying that they had to ask the director of the Gemini South Observatory if they could take this specific time away from other observers in order to host the event. You can watch a recording of the event at the link below.
While Meech set the stage, the telescope team in Chile prepared the giant 26-foot (8-meter) mirror for its delicate work. Inside the control room, the science operations specialists gave us a window into the process: “We are taking calibrations, tuning the telescope and checking the sky conditions … Tonight it’s very dry, with steady winds, perfect for good seeing.”
The comet stuck with me, as it was only recently that the area had been dusted with snow. While the Gemini South Observatory wasn’t as badly hit with precipitation, lower down, its neighbor, the Atacama Large Millimeter/submillimeter Array (ALMA) facility on the Chajnantor Plateau, had enough snow that it temporarily suspended all science operations. Thankfully, the snow had melted by the time of the live event, allowing for everything to proceed as smoothly as possible.
As the calibrations continued for an hour, Meech answered questions and hyped the audience up for when the comet could be spotted: “We just don’t know what we’re going to see tonight, and that’s exciting.”
Before Gemini South began looking, both Hubble and JWST had already taken an early look. Hubble estimated the comet’s nucleus, or core, to be less than 1.86 miles (3 kilometers) across, buried under a halo of dust and gas. JWST, meanwhile, struggled to see the nucleus because of that halo, revealing that 3I/ATLAS seems to be unusually rich in carbon dioxide. That makes it different from its predecessor 2I/Borisov, the second interstellar comet ever detected, which had far more carbon monoxide.
Meech and the others at Gemini Southhoped to see if they could confirm that 3I/ATLAS does in fact have lots of carbon dioxide, or dry ice, which would burn off as the comet got closer to the sun. Meech explained that the comet’s closest approach to the sun will be in October, but it will be impossible to spot as the comet moves behind the sun at that time. She mentioned that NASA scientists are currently discussing whether existing spacecraft could be temporarily repurposed to observe 3I/ATLAS on the other side of the sun, removing this blind spot.
Even if this isn’t the case, observations can resume in November when 3I/ATLAS re-emerges from behind the sun, and, depending on its activity and chemical composition, the comet could appear even brighter as it burns off more gas and dust. But even if 3I/ATLAS does indeed brighten up, the window for scientists to study it will still be limited.
“Once these objects get too faint to see, they will never be seen again,” Meech said. “They are just passing through our solar system. Even 1I/’Oumuamua is still within our solar system. It is out in the vicinity of the Kuiper Belt now.”
‘Oumuamua is the first interstellar object ever spotted in our solar system. Astronomers detected it back in 2017.
As the telescope began turning toward 3I/ATLAS, a hush fell over the experts as everyone watched the shared screen of the scientists in the Gemini South control room. Meech had explained earlier that the first chemical they hoped to see using the GMOS was cyanide, as it interacts with sunlight.
Then came the first image, a bright, blurry smudge. There was a collective gasp as we all saw it, and the event chat was full of surprise and excitement.
“You’re looking at a building block of someone else’s home,” Meech said. However, she added, “it’s impossible to backtrack the comet based on its trajectory, as everything else is also moving around it.”
The first images showed a faint but distant glow of a developing tail, confirmation that this visitor was behaving more like a “classic” comet than the odd, elongated ‘Oumuamua, which Meech had also studied.
“This is the raw image,” she said. “I bet you once this image is further calibrated, this will have a longer tail.”
Along with taking the spectra, the scientists measured the comet’s brightness, comparing 3I/ATLAS’s reflected sunlight to their reference points. This resulted in an estimated color and luminosity, suggesting that 3I/ATLAS is faint but steadily active, releasing gas and dust even at its current considerable distance from the sun.
Before the experts could dive any further in, the hosts of the event decided that two hours was enough time for one night. With the spectra captured and brightness measured and plenty of questions unanswered, the session wrapped on a note of anticipation, with many of us wishing we could return to the control room at Gemini South Observatory.
Thankfully, the Shadow the Scientists Initiative is planning another public viewing event after 3I/ATLAS re-emerges from the sun, this time using the Gemini North Observatory, which I for one am excited to join.
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