On November 26, 2025, astronomers used the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North Telescope on Maunakea, Hawaii, to image interstellar comet 3I/ATLAS. New observations show how the object changed after its closest approach to the Sun.
In this image taken by the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North Telescope on Maunakea in Hawaii, half of the Gemini International Observatory partially funded by NSF and operated by NSF's NOIRLab, 3I/ATLAS zooms through stars and galaxies. Image credit: Gemini International Observatory / NOIRLab / NSF / AURA / B. Bolin / J. Miller and M. Rodriguez, Gemini International Observatory and NOIRLab NSF / TA Chancellor, University of Alaska Anchorage and NOIRLab NSF / M. Zamani, NOIRLab NSF.
3I/ATLAS reached its closest approach to the Sun, known as perihelion, on October 30, 2025.
Emerging from behind the Sun, the interstellar visitor reappeared in the sky near Zania, a triple star system located in the constellation Virgo.
On November 26, 2025, Eureka Scientific researcher Bryce Bolin and his colleagues captured new images of the comet as part of a public initiative organized by NSF NOIRLab in collaboration with Shadow the Scientific.
“Sharing observing experiences under the best available conditions gives the public a front-row view of our interstellar guest,” Dr. Bolin said.
“Giving the public the opportunity to see what we do as astronomers and how we do it also helps clarify the scientific and data collection process, adding transparency to our study of this amazing object.”
The 3I/ATLAS image, taken by the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope, shows a comet's coma, a cloud of gas and dust that forms around the comet's icy nucleus in the vicinity of the Sun. Image credit: Gemini International Observatory / NOIRLab / NSF / AURA / B. Bolin / J. Miller and M. Rodriguez, Gemini International Observatory and NOIRLab NSF / TA Chancellor, University of Alaska Anchorage and NOIRLab NSF / M. Zamani, NOIRLab NSF.
The new GMOS images consist of images taken through four filters: blue, green, orange and red.
“During imaging, the comet remains fixed in the center of the telescope's field of view,” the astronomers said.
“However, the position of the stars in the background relative to the comet changes, causing them to appear as streaks of color in the final image.”
“In earlier images of the comet taken during the Scientist's Shadow session at Gemini South in Chile, it appears red in color.”
“However, in new images released today, it has a faint greenish glow.”
“This is due to light emitted by gases in the comet's coma that evaporate as the comet heats up, including diatomic carbon, a highly reactive molecule of two carbon atoms that emits light at green wavelengths.”
“What remains unknown is how the comet will behave once it leaves the Sun's vicinity and cools down.”
“Many comets have a delay in responding to solar heat due to the delay in time it takes for the heat to travel through the comet's interior.”
“The delay could activate the evaporation of new chemicals or trigger a cometary flare.”
