Introduction to 3I/ATLAS
The interstellar comet 3I/ATLAS has captivated astronomers since its discovery on July 1, 2025. This celestial visitor, originating from the depths of interstellar space, is only the third known object of its kind, and its point of origin remains shrouded in mystery.
Discovered by the Deep Random Survey remote telescope in Chile, part of the ATLAS (Asteroid Terrestrial-impact Last Alert System) project, scientists have mobilized to observe this comet with an eager public clamoring for further insights. Both NASA’s Hubble Space Telescope and the James Webb Space Telescope have recently captured images of this icy wanderer as it approaches the sun.
Live Webcast at Gemini South Observatory
When I learned that the Gemini South Observatory in Chile was airing a live webcast as part of the Shadow the Scientists (StS) initiative—designed to engage the public with ongoing research—I was eager to participate. The livestream commenced with a backstage look into the control room at Gemini South, where astronomers prepared to calibrate the telescope. The team aimed to utilize the GMOS (Gemini Multi-Object Spectrographs) alongside the new Gemini High-resolution Optical SpecTrograph (GHOST) instrument to analyze the comet’s chemical makeup.
Insights from Experts
Astronomer Karen Meech from the Institute for Astronomy at the University of Hawai’i emphasized the significance of such opportunities, stating, “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 echoed Meech’s sentiments, noting their need to request specific telescope time from the director of the Gemini South Observatory to facilitate the live event. The recording of this unique experience is available for viewing.
Observational Challenges
As preparations continued, the telescope team skillfully adjusted the giant 26-foot (8-meter) mirror for its mission. Inside the control room, science operations specialists provided insights into the calibration process, mentioning, “We are taking calibrations, tuning the telescope and checking the sky conditions … Tonight it’s very dry, with steady winds, perfect for good seeing.”
Despite recent snowfall affecting nearby facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA), the weather at Gemini South remained stable, allowing the event to proceed seamlessly.
Anticipation Builds
As the calibrations progressed over the hour, Meech engaged with the audience, sharing her excitement for the upcoming observations: “We just don’t know what we’re going to see tonight, and that’s exciting.” Hubble had previously estimated the comet’s nucleus to be less than 1.86 miles (3 kilometers) across, obscured by a halo of dust and gas, while JWST had revealed that 3I/ATLAS is unusually rich in carbon dioxide compared to its predecessor, 2I/Borisov.
Meech and her team hoped to confirm the presence of carbon dioxide—a compound that would subliminate as the comet approaches the sun. She mentioned that while 3I/ATLAS’s closest encounter with the sun will occur in October, it will be invisible as it moves behind the sun. There’s ongoing discussion within NASA about repurposing existing spacecraft to observe 3I/ATLAS from that angle.
Observation Results
Even though observations would resume in November, once the comet reappears, time to study it will remain limited. Meech cautioned, “Once these objects get too faint to see, they will never be seen again.” She noted that even 1I/’Oumuamua, the first interstellar object detected in our solar system in 2017, is now far out in the Kuiper Belt.
As the telescope finally aligned with 3I/ATLAS, a hush fell over the experts in the control room. Meech explained that the first substance the team aimed to detect with GMOS was cyanide, as it reacts with sunlight.
Then, the moment arrived— the first image appeared as a bright yet blurry smudge. Gasps echoed through the virtual audience, as excitement surged. “You’re looking at a building block of someone else’s home,” Meech remarked, though she added a note of caution, stating, “it’s impossible to backtrack the comet based on its trajectory, as everything else is also moving around it.” The initial images revealed a faint but growing tail, suggesting that this comet behaved more like a traditional comet compared to the peculiar, elongated ‘Oumuamua.
Meech noted, “This is the raw image. I bet you once this image is further calibrated, this will have a longer tail.” In addition to capturing the spectra of the comet, scientists assessed its brightness, relating 3I/ATLAS’s reflected sunlight to reference points, leading to estimates of color and luminosity. The findings indicated that 3I/ATLAS, while faint, is actively producing gas and dust even at its considerable distance from the sun.
As the session drew to a close after two hours of observation, the hosts acknowledged that while they had gathered significant data, many questions remained. The event concluded with a strong sense of anticipation, with many participants expressing a desire to return to the control room for further studies.
Fortunately, the Shadow the Scientists Initiative has plans for another public viewing event once 3I/ATLAS re-emerges from behind the sun, using the Gemini North Observatory—a prospect I eagerly await.
