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Gemini South Captures Lengthening Tail of Interstellar Comet 3I/ATLAS

Researchers report a CO2‑heavy coma, with global teams preparing continued monitoring toward a late‑October perihelion near Mars.

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’s GMOS shows a broad coma and a newly more prominent tail.
  • Program lead Karen Meech’s team measured colors and took spectra, indicating dust and ice resembling those of typical Solar System comets.
  • Complementary data from four NASA telescopes point to an unusually high CO2-to-water ratio in the coma.
  • A new arXiv preprint led by Yiyang Guo favors a Milky Way thin‑disk origin but identifies no definitive source star despite 25 close stellar passages in simulations.
  • The visitor is the third confirmed interstellar object and is expected to reach perihelion in late October near Mars.