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ALMA Finds Extreme Heavy-Water Ratio in Interstellar Comet 3I/ATLAS

The result suggests the comet formed far from its star in a deep-freeze zone beyond where carbon dioxide turns to ice.

Overview

  • A peer-reviewed study reports a deuterium-to-hydrogen ratio of about 6.6×10^-3 in the comet’s water, roughly 40 times Earth’s oceans and about 30 times typical Solar System comets.
  • Scientists say such strong deuterium enrichment points to formation in a much colder, low-radiation region on the outer edge of a protoplanetary disk.
  • The team measured deuterated water in the gas around the nucleus using the ALMA radio array, with supporting observations from the University of Michigan’s MDM Observatory.
  • Other data show unusually high carbon dioxide ice and strong methanol outgassing, marking a volatile mix unlike most comets born in our Solar System.
  • 3I/ATLAS is only the third known interstellar visitor, it is now heading back into deep space, and its exact home star remains unknown.