New analyses of 3I/ATLAS are beginning to emerge, and they point to an unusual composition. According to a report from Phys.org, the interstellar comet has an extreme preference for heavy water, meaning its water content is substantially enriched in deuterium, the heavier isotope of hydrogen. Heavy water is rare in most Solar System objects, so such a strong signature could help researchers understand where the object formed.
The object was discovered in July 2025, making it the third interstellar visitor known to science. Because it appeared suddenly and moved quickly, some of the world's most powerful observatories were trained on it to capture as much data as possible. As those data work through the scientific process, more details about its composition and history are being revealed.
This latest finding about its heavy-water abundance adds a new constraint for models of how planetary systems form and what kinds of ices they send into interstellar space.