Never-before-seen ices detected in the solar system

Trans-Neptunian Objects (TNOs) refer to the primitive small bodies in the outer regions of our Solar System, orbiting beyond Neptune. Formed quite far from the Sun, these objects still hold valuable information about their formation over 4 billion years ago, unlike dwarf planets such as Pluto which may have undergone significant internal evolution.


TNOs have also witnessed planetary migration processes that have redistributed most of them far from their formation regions. To date, observations of TNOs have been limited, providing only a partial characterization of their chemical composition: only water and methanol ices were detected on a handful of objects.

A major observation program by the James Webb Space Telescope recently provided the first comprehensive view of TNOs. The observations of 59 objects obtained with the NIRSpec instrument were analyzed by an international research team involving scientists from CNRS Earth & Universe. The infrared spectra reveal the very first detections of CO₂ and CO ices on small bodies in the outer Solar System.

Against all odds, CO₂ is very widespread, present on 95% of the objects although in varying proportions. While CO is not stable in the trans-Neptunian region, it is nonetheless detected alongside CO₂ on 47% of the objects. This diversity in composition, reflected by variations in abundance as well as the physicochemical state of the ice, will help to trace the history of TNOs to pinpoint their formation location in the protoplanetary disk.

If CO₂ could have been inherited from the protoplanetary disk, CO is more likely formed through the interaction of the surface with solar wind and cosmic rays. Remarkably, ¹³CO₂ is also detected, which opens up the possibility of studying the isotopic ratio of carbon across the outer Solar System.


Reference:
De Prá, M.N., Hénault, E., Pinilla-Alonso, N. et al.
Widespread CO₂ and CO ices in the trans-Neptunian population revealed by JWST/DiSCo-TNOs.
Nat Astron (2024).