JWST observations of Chiron: A unique active Centaur beyond 18 AU

Wong, Ian; Protopapa, Silvia; Holler, Bryan; Villanueva, Geronimo; Guilbert-Lepoutre, Aurelie; Brunetto, Rosario; Pinilla-Alonso, Noemí; Licandro, Javier; De Souza Feliciano, Ana Carolina; Fernandez-Valenzuela, Estela; Stansberry, John; Emery, Joshua
Bibliographical reference

AAS/Division for Planetary Sciences Meeting Abstracts

Advertised on:
10
2024
Number of authors
12
IAC number of authors
1
Citations
0
Refereed citations
0
Description
Chiron is the second-largest Centaur, with an effective diameter of 210 km, and is among the most well-studied minor bodies in the middle and outer Solar System. Notably, Chiron belongs to the enigmatic subpopulation of active Centaurs and has displayed cometary activity several times since its discovery. In March 2021, Chiron underwent an outburst at a heliocentric distance of 18.8 AU while it was near its aphelion passage. This report of Centaur activity is the most distant to date by a significant margin and challenges our prevailing understanding of the mechanisms that trigger and sustain outgassing on these objects. In January 2024, we obtained observations of Chiron with the Near Infrared Spectrograph on JWST as part of Cycle 2 Director's Discretionary Time (DDT) Program 4621 (PI: Ian Wong), following up on earlier spectra from Cycle 1 Guaranteed Time Observation (GTO) Program 1273 (PI: Jonathan Lunine). The higher-spectral-resolution DDT spectrum spans 1.7–5.1 microns and reveals a wide range of surface ices, including a rich assortment of CO2 ice absorption features that are consistent with micron-sized aggregates of H2O and CO2 ice, analogous to the findings derived from previous observations of comets. We measured the production rate of outgassed CH4 (1.6 x 1027 molec/s) and CO2 (1.0 x 1026 molec/s); crucially, no CO production was detected above the noise level. The detection of CH4 is the first of its kind among active Centaurs. Meanwhile, the spatial information from the integral field unit yielded detailed maps of the gaseous constituents within the coma, with the spatially uncorrelated CH4 and CO2 coma maps pointing to distinct regions of sublimation for the two molecules. In this talk, I will present the results of our DDT observations of Chiron, place Chiron within the context of other active bodies observed with JWST, and discuss the broader implications for our understanding of distant cometary activity and the formation and evolution of icy planetesimals throughout the Solar System. Special attention will be given to comparing the results from the DDT and GTO observations and assessing the time evolution of Chiron's coma during its ongoing period of activity.