A new image of the interstellar comet 3I/ATLAS indicates that it is becoming more active as it travels through our inner Solar System. This remarkable image was captured by both astronomers and students using the Gemini South telescope located at Cerro Pachón in Chile. The photo showcases the expanding tail of comet 3I/ATLAS alongside a luminous coma, while also providing fresh data that enhances our understanding of its composition.
Comet 3I/ATLAS was first discovered on July 1, 2025, by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile. As an interstellar comet, it formed around a distant star in the cosmos. Unlike the vast majority of comets that originate from within our Solar System, 3I/ATLAS is only the third known comet to come from beyond our Solar System. After entering our Solar System from the depths of space, it will eventually make its exit back into the interstellar void.
Since its discovery, 3I/ATLAS has been observed by some of the most powerful telescopes worldwide, both terrestrial and space-based, including the Very Large Telescope, the Gemini North Telescope, the Hubble Space Telescope, SPHEREx, and the James Webb Space Telescope. These observations have provided invaluable insights into the comet's chemical makeup, size, and trajectory, and there is even evidence suggesting that 3I/ATLAS may be the oldest comet humanity has ever encountered.
In the coming months, 3I/ATLAS is set to make close passes of the Sun, Earth, Mars, and Jupiter. Its proximity may allow visibility for rovers and orbiters stationed at Mars and Jupiter, offering a unique opportunity for further observations.
Recent observations made with the Gemini South telescope on August 27, 2025, revealed a prominent tail and glowing coma extending from 3I/ATLAS. These observations have enabled scientists to gather new measurements concerning the comet's colors and composition. The team utilized the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to capture detailed, multi-colored images of the comet, showcasing a broad 'coma'—the cloud of gas and dust surrounding the comet's nucleus, which forms as ice and dust heat up when the comet approaches the Sun.
The new images illustrate a significantly longer tail than previously captured, indicating that 3I/ATLAS has become more active as it journeys through the inner Solar System. The team also collected information on the emitted light from the comet—which is known as its spectrum—providing deeper insights into its composition and chemical changes as it navigates through our Solar System. Notably, these observations suggest that the dust and ice comprising 3I/ATLAS resemble those found in comets formed within our own Solar System, indicating that both types of comets may share similar formation processes. This finding is vital for cometary scientists.
The captivating images of 3I/ATLAS taken by Gemini South were part of a collaborative initiative that included both scientists and public participants, notably students from Hawai‘i and La Serena, Chile. Students were invited to remotely connect to the Gemini South control room, engaging with astronomers and posing questions about the science of interstellar comets. Participants joined from various locations, including Europe, New Zealand, and South America. The program was spearheaded by Karen Meech, an astronomer at the University of Hawai‘i Institute for Astronomy.
In reflecting on the observations, Meech stated, “The primary objectives were to analyze the comet’s colors, which provide clues about the composition and sizes of the dust particles in the coma, and to gather spectra for a direct measurement of the chemistry. We were thrilled to see the growth of the tail, indicating a change in the particles from previous images, and we gained our first insights into the comet's chemistry from the spectrum.”
As 3I/ATLAS speeds back into the depths of interstellar space, this remarkable image serves as both a significant scientific milestone and a source of awe. It highlights that our Solar System is merely a segment of a much larger and dynamic galaxy, where even the briefest visitors can leave a lasting impact.
This public outreach initiative was organized by NSF NOIRLab in collaboration with Shadow the Scientists, a project designed to connect the public with scientists and engage them in authentic scientific experiments, including astronomy observing experiences using world-class telescopes.
