Low-activity Main-belt Comet 133P/Elst-Pizarro: New Constraints on Its Albedo, Temperature, and Active Mechanism from a Thermophysical Perspective
Abstract
133P/Elst-Pizarro is the first recognized main-belt comet, but we still know little about its nucleus. First we use mid-infrared data of Spitzer MIPS, Spitzer IRS, and the Wide-field Infrared Survey Explorer to estimate its effective diameter, ${D}_{\mathrm{eff}}={3.9}_{-0.3}^{+0.4}$ km, geometric albedo, ${p}_{{\rm{v}}}=0.074\pm 0.013$ , and mean Bond albedo ${A}_{\mathrm{eff},{\rm{B}}}=0.024\pm 0.004$ . The albedo is used to compute 133P's temperature distribution, which shows significant seasonal variation, especially polar regions, ranging from ∼40 to ∼200 K. Based on current activity observations, the maximum water gas production rate is estimated to be $\sim 1.4\times {10}^{23}\,{{\rm{s}}}^{-1}$ , being far weaker than $\sim {10}^{26}\,{{\rm{s}}}^{-1}$ of JFC 67P at a similar heliocentric distance of ∼2.7 au, indicating a thick dust mantle on the surface to lower down the gas production rate. The diameter of the sublimation area may be <∼200 m according to our model prediction. We thus propose that 133P's activity is more likely to be caused by sublimation of a regional near-surface ice patch rather than a homogeneous buried ice layer. Such a small near-surface ice patch might be exposed by one impact event, before which 133P may be an extinct comet (or ice-rich asteroid) with an ice layer buried below ∼40 m depth. The proposed ice patch may be located somewhere within latitude -50 ∼ 50° by comparing theoretical variation of sublimation temperature to the constraints from observations. The timescale to form such a thick dust mantle is estimated to be >100 Myr, indicating that 133P may be more likely to be a relatively old planetesimals or a member of an old family than a recently formed fragment of some young family.
- Publication:
-
The Astronomical Journal
- Pub Date:
- February 2020
- DOI:
- 10.3847/1538-3881/ab61f7
- arXiv:
- arXiv:1912.06266
- Bibcode:
- 2020AJ....159...66Y
- Keywords:
-
- None;
- Comets;
- Asteroid belt;
- Small Solar System bodies;
- 1065;
- 280;
- 70;
- 1469;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 11 pages, 9 figures, accepted for publication in The Astronomical Journal