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4d ago

Interstellar Visitor 3I/ATLAS Shows Growing Tail as New Study Finds No Parent Star

Multi-telescope spectra reveal an unusually CO2‑rich coma that likely explains the object's early activity far from the Sun.

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

  • Gemini South images from August 27 show a broad coma and a lengthening tail, confirming active cometary behavior from the third known interstellar object.
  • Gemini’s GMOS observations targeted color and chemistry, with early results indicating dust and ice similar to Solar System comets.
  • Independent space‑telescope measurements report a CO2‑dominated coma, a rare composition that accounts for activity at larger heliocentric distances.
  • A new arXiv analysis integrating the orbit 10 million years backward with Gaia DR3 stars found numerous close passes but no plausible stellar source, with kinematics consistent with the Galactic thin disk.
  • 3I/ATLAS is projected to reach perihelion near Mars around October 29, 2025, will not cross Earth’s path, and will head back into interstellar space; the Gemini observing run also engaged students via NOIRLab’s Shadow the Scientist program.