JWST mid-infrared spectroscopy of centaurs and small trans-Neptunian objects: Linking the inner and outer Solar System

¹ Aix-Marseille University, CNRS, CNES, LAM, Institut Origines, 38 rue Frédéric Joliot Curie, 13388 Marseille, France
² Florida Space Institute, University of Central Florida, 12354 Research Parkway, Partnership 1 building, Orlando, FL, 32828, USA
³ Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France
⁴ Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁵ European Southern Observatory (ESO), Alonso de Cordova 3107, 1900 Casilla Vitacura, Santiago, Chile
⁶ Institute of Space Science and technology of Asturias, University of Oviedo, Oviedo, Spain
⁷ University of Central Florida, Department of Physics, Orlando, FL 32816, USA
⁸ Instituto de Astrofísica de Canarias (IAC), La Laguna, Spain; Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Spain
⁹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

^★ Corresponding author.

Received: 8 April 2025
Accepted: 28 May 2025

Abstract

Context. A fraction of the small bodies that formed in the outer Solar System (beyond Uranus and Neptune) are predicted to have been implanted in the inner Solar System (P- and D-type asteroids and Jupiter trojans) following the outward migration of these two planets (Nice model).

Aims. We further test the hypothesis that small bodies in the inner and outer Solar Systems share a common origin. This is achieved by measuring and comparing the silicate composition of centaurs and small trans-Neptunian objects (TNOs) with that of P- and D-type asteroids and Jupiter trojans. Silicates are thermally stable over the heliocentric range extending from the main asteroid belt to the Kuiper belt. They currently appear to be the only reliable indicator of a shared genetic link.

Methods. Spectroscopic data were obtained with JWST/MIRI for three centaurs (Chariklo, Bienor, and 2020 VF1) and three scattered-disk objects (1999 OX3, 2002 GG166, and 2013 LU28) with a centaur-like orbit as part of the Cycle 2 GO program (GO 2820). We also analyzed the MIRI data of GTO target 2013XZ8, which is also a centaur (Cycle 1 GTO 1272), and of three Jupiter trojans (targets of the Cycle 1 GO 2574 program).

Results. The emissivity spectra of centaurs and small TNOs, including the variability in the spectral contrast of the main 10 μm silicate feature, are remarkably similar to those of Jupiter trojans, P- and D-type main-belt asteroids, and comets. In particular, the spectral contrast observed for the cliff-type target 1999 OX3 is close to that observed for comet comae, suggesting substantial surface porosity that is probably related to a lower silicate-to-ices+organics ratio. The analysis of the emissivity spectra of centaurs, small TNOs, and Jupiter trojans revealed very many features that are consistent with the hypothesis that the surfaces of these objects contain significant amounts of crystalline olivine and pyroxene (with Mg/(Mg+Fe) ≥ 0.7).

Conclusions. The JWST/MIRI observations of centaurs and small TNOs support the hypothesis that these bodies share a common origin with inner Solar System P- and D-type asteroids and Jupiter trojans, as outlined in the Nice model. Together with previous measurements for these populations and dynamical studies, our results raise the possibility of a genetic link between P-type and bowl-type targets and between D-type and cliff-type targets.