Overview
- An international team published UVES measurements in Nature Astronomy this week reporting unusually high carbon and nitrogen isotopic ratios in the gas around 3I/ATLAS.
- Researchers used the UVES spectrograph on ESO’s Very Large Telescope to measure isotopes in cyanide molecules, with lead authors including Cyrielle Opitom, Jean Manfroid and Damien Hutsemékers.
- The isotopic proportions are higher than those seen in Solar System comets and imply 3I/ATLAS formed in the outer regions of a low‑metallicity star system, with age estimates exceeding about 9 billion years.
- The comet’s exceptional brightness during its visit made these high‑precision measurements possible, and the object passed closest to Earth on 19 December 2025, unlike the fainter 1I/ʻOumuamua and 2I/Borisov.
- VLT monitoring is winding down as 3I/ATLAS recedes, leaving a finite dataset that gives a rare chemical probe of early galactic planetesimal chemistry and points to the ELT as the tool needed to study fainter future interstellar visitors.