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

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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 ) values for the three MBCs for which water vapor outgassing has been successfully detected that are consistent within uncertainties with an average value of log ( A f ρ / Q H 2 O ) = − 24.6 ± 0.2 . Lastly, we find no clear correlations of water production rates with nucleus size, semimajor axis, or heliocentric distance among MBCs observed by JWST so far, but would particularly encourage future JWST observations of additional MBCs interior to the 5A:2J mean-motion resonance with Jupiter and at high inclinations, as well as multiple observations of MBCs during single active apparitions to further investigate areas of interest identified from the current sample of JWST-observed MBCs.
Funding Information
  • Space Telescope Science Institute (NAS 5-03127)
  • NASA ∣ SMD ∣ Planetary Science Division (80NSSC19K0869)
  • NASA ∣ SMD ∣ Planetary Science Division (80NM0018D0004)

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