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

The heavy‑hydrogen signal points to a birth in deep cold far from other newborn stars.

Overview

  • A peer-reviewed Nature Astronomy study reports the first detection of semi-heavy water in an interstellar comet using ALMA, with Chilean astronomer Tere Paneque leading the observing work.
  • The team measured unusually high levels of deuterium, a heavy form of hydrogen that swaps into water to make HDO.
  • That chemical mix points to formation in an extremely cold, isolated region, possibly before the comet’s parent star existed.
  • The object is already beyond Jupiter and moving away at about 220,000 km/h, which limits chances for more detailed follow-up.
  • It is only the third confirmed interstellar visitor after ‘Oumuamua and 2I/Borisov, offering a rare look at material from another star system.