Discovery of three groups of icy planetary bodies in the outer Solar System

The DiSCo program, thanks to the James Webb telescope, identifies three types of TNOs whose chemical composition, linked to their origin in the protoplanetary disk, sheds light on the formation of planetesimals and the dynamic evolution of the primitive Solar System.

Work from the Discovering the Composition of Trans-Neptunian Objects (DiSCo) program published in Nature Astronomy has discovered the existence of three main groups of trans-Neptunian objects (TNOs) in the outer Solar System. Thanks to the spectroscopic capabilities of the James Webb Space Telescope (JWST), these studies reveal for the first time a molecular composition that tells us about the formation and early evolution of planetesimals in the protoplanetary disk.

TNOs, planetary bodies located beyond Neptune, are icy remnants of the early Solar System. Deflected towards orbits closer to the Sun in the region of the giant planets, some become Centaurs, precursors of Jupiter-like comets.

The DiSCo study distinguishes three groups of TNOs according to their surface composition, linked to the "ice retention lines" of the protoplanetary disk. External TNOs, such as the "cold classics", contain a lot of methanol and organic compounds, while those formed near giant planets have water ice and silicates. TNOs formed in intermediate regions are rich in carbon dioxide. These results establish for the first time a direct correlation between the chemistry of planetesimals and their origin in the protoplanetary disk.

Centaurs show distinct spectral signatures from their trans-Neptunian precursors. As they approach the Sun, their surface is altered by thermal processes. The studies thus reveal the key role of dynamical and thermal evolution in the current structuring of small icy bodies. They open a new window on the genesis of planetesimals and enrich our understanding of the chemical and dynamical architecture of the early Solar System.

Artistic representation of the distribution of trans-Neptunian objects in the planetesimal disk, with overlaid representative spectra of each compositional group highlighting the dominant molecules on their surfaces. Credit: Graphic art by William D. González Sierra for the Florida Space Institute, University of Central Florida

Contacts at IAS:

Rosario Brunetto, CNRS,  IAS / OSUPS  rosario.brunetto @ universite-paris-saclay.fr

Elsa Hénault, Université Paris-Saclay,  IAS / OSUPS elsa.henault @ universite-paris-saclay.fr

Links to the online publications:

https://www.nature.com/articles/s41550-024-02433-2

https://www.nature.com/articles/s41550-024-02417-2