Interstellar Comet 3I/ATLAS Displays Broad Coma and Growing Tail
Sep 4, 2025
Using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope at NSF’s International Gemini Observatory in the Chilean Andes, astronomers have captured new multi-color images of the interstellar comet 3I/ATLAS.
3I/ATLAS was discovered by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, on July 1, 2025.
The comet will reach its closest approach to the Sun around October 30, 2025, at a distance of 1.4 AU (210 million km, or 130 million miles) — just inside the orbit of Mars.
In the new Gemini/GMOS images, GMOS displays a broad coma and a tail spanning about 1/120th of a degree in the sky and pointing away from the Sun.
These features are significantly more extended than they appeared in earlier images of the comet, showing that 3I/ATLAS has become more active as it travels through the inner Solar System.
The new observations also suggest that the dust and ice of the comet are broadly similar to solar system comets, hinting at shared processes in the formation of planetary systems around other stars.
“As 3I/ATLAS speeds back into the depths of interstellar space, these images are both a scientific milestone and a source of wonder,” said Dr. Karen Meech, an astronomer with the Institute for Astronomy at the University of Hawai’i.
“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.”
More than just capturing stunning images, the main scientific motivation of the observing session was to collect the comet’s spectrum, which refers to the wavelengths of light that it emits.
A spectrum can tell scientists information about the comet’s composition and chemistry, which allows them to understand how the comet changes as it passes through the Solar System.
“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,” Dr. 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 observations provide both a breathtaking view and critical scientific data,” said Dr. Bryce Bolin, a researcher at Eureka Scientific.
“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.”
https://www.sci.news/astronomy/interstellar-comet-3i-atlas-broad-coma-growing-tail-14192.html
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