Credit: ESO/C. Opitom, J. Manfroid et al. Comet image: O. Hainaut

This image shows part of the spectrum of interstellar comet 3I/ATLAS, captured between 6 and 26 December 2025 with the UVES instrument on ESO’s Very Large Telescope (VLT). Using UVES, astronomers studied the spectral signatures of cyanide, a molecule comprised of a carbon atom and a nitrogen one. More precisely, they looked at their isotopic ratios: the relative amounts of different forms of the same atoms. These ratios are sensitive to the conditions under which 3I/ATLAS formed, and are not expected to change much as the comet travels through space. The spectrum shown here contains spectral features produced by 12C, an isotope of carbon with 6 protons and 6 neutrons, and 13C, which has 7 neutrons instead. These features are very faint, but astronomers know the exact wavelength regions where to look for them in the spectrum of the comet. Adding together several of these wavelength regions averages out the noise, making the real features pop out. The team performed similar measurements with two isotopes of nitrogen, 14N and 15N. By comparing the 12C/13C and 14N/15N ratios with those measured in Solar System comets and in the discs of material around young stars, the team concluded that 3I/ATLAS likely formed in the outskirts of the disc around a star older than the Sun.

Provider: European Southern Observatory

Image Source: https://www.eso.org/public/images/eso2608b/

Curator: European Southern Observatory, Garching bei München, None, Germany

Image Use Policy: Creative Commons Attribution 4.0 International License