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Interstellar Comet 3I/ATLAS Grows a Tail as New Analysis Points to Thin-Disk Origins

Fresh Gemini measurements reveal CO2‑rich activity ahead of a late‑October perihelion near Mars’ orbit.

The Gemini South telescope captured new images of the interstellar comet 3I/ATLAS, which will make its closest approach to Earth in October.
Image
Comet 3I/ATLAS streaks across a dense star field in this image captured by the Gemini Multi-Object Spectrograph (GMOS) on Gemini South at Cerro Pachón in Chile, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab. This image is composed of exposures taken through four filters — red, green, blue and ultraviolet. As exposures are taken, the comet remains fixed in the center of the telescope’s field of view. However, the positions of the background stars change relative to the comet, causing them to appear as colorful streaks in the final image. See a version of the image where the stars have been “frozen” here. These observations of Comet 3I/ATLAS were conducted during a Shadow the Scientists program hosted by NSF NOIRLab. A full recording of the session can be found here. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the Scientist Image Processing: J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab), T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani (NSF NOIRLab)

Overview

  • An August 27 image from Gemini South shows 3I/ATLAS with a brightening coma and a clearly lengthening tail.
  • Gemini’s GMOS provided initial ground‑based spectra and color data, indicating dust and ices similar to Solar System comets.
  • Earlier space‑telescope observations reported an unusually high carbon‑dioxide abundance relative to water, consistent with early activity at large distances.
  • A new arXiv study using Gaia DR3 finds no stellar flyby in the past 10 million years that explains the object’s path and deems its motion thin‑disk‑like.
  • Perihelion is forecast around October 29, 2025, with a pass near Mars’ orbit and no threat to Earth as coordinated observing campaigns continue.