Characterization of the Volatile Properties of 133P/Elst-Pizarro and Other Main-belt Comets with JWST and Ground-based Observations

Abstract We report results from an analysis of the volatile composition and evolution of the main-belt comet (MBC) 133P/Elst–Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P’s orbit, finding Q H 2 O = ( 1.9 ± 0.6 ) × 1 0 25 molecules s −1 on UT 2024 June 12 (at a true anomaly of ν = 8° and heliocentric distance of r h = 2.674 au), and Q H 2 O = ( 1.4 ± 0.4 ) × 1 0 25 molecules s −1 on UT 2024 October 14 (at ν = 37 . ° 4 and r h = 2.747 au). These measurements nominally represent a decline of ∼25% in Q H 2 O between the visits, although they are also consistent with no change within uncertainties. We do not detect CO, CO 2 , or CH 3 OH, placing 133P’s hypervolatile depletion ( Q CO 2 / Q H 2 O < 0.009 ) at a similar level found for previously observed MBCs. We find log ( A f ρ / Q H 2 O )