A group of astronomers and students have captured a new image of the interstellar comet 3i/Atlas. A tail emerges, never observed before.
Astronomes and students, working side by side thanks to an unprecedented teaching initiative, captured a new breathtaking image of the interstellar comet 3i/Atlas, immortalized with the Gemini South telescope in Chile at 2,722 meters above sea level. The observations, carried out on August 27, 2025 with the Multi-object spectrograde Gemini (a multi-object spectrograde is an astronomical tool that allows you to simultaneously analyze the light from multiple celestial objects, such as galaxies or stars, inside the same field of vision), show a prominent tail (never observed before) and a bright hair (the hair of an comet is a sort of temporary atmosphere that is a temporary atmosphere. When the comet approaches the sun) that extends into space, offering not only a celestial show but also precious scientific data on the composition and colors of this rare cosmic visitor.
Astronomers and students. The event was part of a special NSF Noirlab program in collaboration with Shadow the Scientists, designed to bring the public closer to astronomical research. Connected via Zoom, students from Hawaii, from La Serena and from different parts of the world they were able to witness the operations live, interact with scientists and ask questions about the science of comets. The session led was the astronomer Karen Meech of the University of Hawaii and Bin Yang of the Universidad Diego Portales of Chile, who illustrated the ghostly data and the importance of interstellar objects in the study of the formation of planetary systems.
In the images collected, the comet appears with a wide hair and a tail that extends for about 1/120 of grade in the sky, much longer than previous observations: a clear sign of growing activity as the heat of the sun begins to sublimate its ice.
The objectives. “The purpose of observation was to analyze the colors of the comet and obtain ghosts for a direct measurement of chemistry,” explains Meech. “We were excited to see the growth of the tail together with the students, which indicates a change in the particles issued with respect to the previous images and we had our first taste of its chemistry”. The scientist Bryce Bolin (Eureka Scientific) also took part in the session: “Each interstellar comet is a messenger of another star system. Studying light and color, we begin to understand the diversity of worlds beyond ours ». A second public appointment is already scheduled for November 2025, when 3i/Atlas re -emerges from behind the sun: on that occasion the Gemini North telescope in Hawaii will be the protagonist.
3i/Atlas in the Solar System. Discovered on July 1, 2025 by the Atlas surveillance system, 3i/Atlas is only the third interstellar object never identified, after ʻoumuamua (2017) and 2i/Borisov (2019). Unlike the “local” comets, its hyperbolic orbit will lead her back into the interstellar space, making this step a scientific opportunity unrepeatable.
The images of Gemini South on August 27th mark a milestone: the public and scientists have witnessed the birth of a well-defined anti-rod tail live, a sign that the comet entered a more active phase while crossing the internal solar system.
An ancient body. The observations are not limited to visual spectacularity: together with telescopes such as James Webb and Swift have analyzed the comet in detail, discovering characteristics that make it unique starting from the carbon dioxide/water relationship that is very high (about 8: 1), never observed in other comets, which explains why it has already activated more than the orbit of Jupiter. Furthermore, a significant production of water has been detected (about 40 kilograms per second), a clue that at least 20% of the surface is active.
A unique chemistry. Then there is a more technical data concerning the depletion of carbon chains (very low CNS/CN ratio), a very rare feature. The “depletion of carbon chains” is a phrase that indicates that this comet has a poor presence of complex organic molecules containing carbon, such as carbon monoxide (CO) or longer compounds. In practice, compared to the comets of our Solar System, 3i/Atlas shows a lot of Co₂ (carbon dioxide) but little co, which is unusual.
Finally, the dimensions of the nucleus have been calculated, which should be between 320 meters and 5.6 kilometers and the rotation period, which is 16.16 hours. These data suggest that 3i/Atlas comes from a chemical environment very different from ours and that it formed around a star billions of years ago. Some studies even hypothesize that it may have over 7 billion years, potentially making it the oldest comet ever observed.
And now? The comet will reach Perdie (the closest point) on 29-30 October 2025, at about 1.4 Au from the sun. The slightest distance from the earth will have in December 2025, when it will pass to 270 million kilometers.
“While 3i/Atlas returns to the interstellar space”, concludes Meech, “this image reminds us that we are part of a vast and dynamic galaxy and that even more fleeting visitors can leave a lasting sign”.
