Astronomers have captured a stunning image of a tail growing on interstellar invader Comet 3I/ATLAS. The image was captured on Aug. 27, 2025, by a team of scientists and students using the Gemini South telescope located on Cerro Pachón in Chile.
Discovered on July 1 by the ATLAS (Asteroid Terrestrial-impact Last Alert System), 3I/ATLAS is just the third-ever object found drifting through our solar system that is believed to have originated from around another star. The previous two interstellar intruders were the cigar-shaped ‘Oumuamua (officially designated 1I/2017 U1), discovered drifting through the solar system in 2017, and the comet/asteroid hybrid 2I/Borisov discovered two years later in 2019.
All of these objects offer scientists a unique opportunity to study material from another planetary system, and the growing tail of 3I/ATLAS is a tantalizing glimpse at the material that lies within this comet. But this opportunity is limited; as happened with ‘Oumuamua and 2I/Borisov, 3I/ATLAS’ orbit will eventually carry out of the solar system.
Regardless of whether they originate from the solar system or beyond, when comets like 3I/ATLAS approach the sun, solar radiation heats ices at their hearts. This causes solid ice they carry to change directly into gas, skipping a liquid phase, in a process called “sublimation.” This gas then erupts from the comet, forming its distinctive halo or “coma” and its characteristic tail. As comets get closer to the sun, they express more material and their tails become longer — a process that these new images from Gemini South show happening for 3I/ATLAS.
“As 3I/ATLAS speeds back in to the depths of interstellar space, this image is both a scientific milestone and a source of wonder,” team leader and University of Hawaii Institute for Astronomy astronomer Karen Meech said in a statement. “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.”
The images of 3I/ATLAS were collected in collaboration with the Shadow the Scientists initiative, which connects researchers with the general public as they perform authentic scientific experiments, like catching an interstellar comet with a world-class telescope like Gemini South and its Gemini Multi-Object Spectrograph (GMOS) instrument.
In the image captured by the team, the wide coma of 3I/ATLAS can clearly be seen, as can the interstellar comet’s tail, which stretches out for around 1/120th of a degree in the sky (one degree is about the width of your little finger as viewed with your arm outstretched). As expected, as 3I/ATLAS approaches the sun and becomes more active, these features have grown since the comet was last imaged.
Beyond the aesthetic value of the images, this sighting of 3I/ATLAS allows scientists to observe the wavelengths of light, or spectrum, it emits. This is useful because different chemicals emit and absorb light at their own characteristic wavelengths, which means the chemical contents of 3I/ATLAS leave their “fingerprints” in the spectrum from the comet’s coma and tail.
“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,” Meech said. “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.”
These new observations suggest that the chemical composition of 3I/ATLAS is similar to that of comets that originate in the solar system. Because comets are formed at the same time as the planets and asteroids of a planetary system, this suggests that the processes that formed the planets of the solar system around 4.6 billion years ago are common to other planetary systems around stars other than the sun.
The Gemini South telescope will get another chance to examine 3I/ATLAS when it emerges from the other side of the sun in November 2025, and scientists are already looking forward to this rare opportunity.
“These observations provide both a breathtaking view and critical scientific data,” Bryce Bolin, research scientist from Eureka Scientific, who assisted the team in making these observations, said. “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.”