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 firstly recognized main-belt comet, but we still know little about its nucleus. Firstly we use mid-infrared data of Spitzer-MIPS, Spitzer-IRS and WISE to estimate its effective diameter $D_{\mathrm{eff}}=3.9_{-0.3}^{+0.4}$ km, geometric albedo $p_{\mathrm{v}}=0.074\pm 0.013$ and mean Bond albedo $A_{\mathrm{eff},\mathrm{B}}=0.024\pm 0.004$. The albedo is used to compute 133P's temperature distribution, which shows significant seasonal variation, especially polar regions, ranging from $\sim 40$ to $\sim 200$ K. Based on current activity observations, the maximum water gas production rate is estimated to be $\sim 1.4\times 10^{23}{\mathrm{s}}^{-1}$, being far weaker than $\sim 10^{26}{\mathrm{s}}^{-1}$ of JFC 67P at similar helio-centric distance $\sim 2.7$ AU, indicating a thick dust mantle on the surface to lower down the gas production rate. The diameter of the sublimation area may be $<\sim 200$ m according to our model prediction. We thus propose that 133P's activity is more likely to be caused by sublimation of regional near-surface ice patch rather than homogeneous buried ice layer. Such 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 ice layer buried below $\sim$40 m depth. The proposed ice patch may be located somewhere within latitude $-50\sim 50^{\circ }$ by comparing theoretical variation of sublimation temperature to the constraints from observations. The time scale 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.

11 pages, 9 figures, accepted for publication in The Astronomical Journal

References in corpus (2)

• Albedos of Main-Belt Comets 133P/Elst-Pizarro and 176P/LINEAR
• The Main-Belt Comets: The Pan-STARRS1 Perspective

Cited by in corpus (3)

• Thermophysical Modeling of 20 Themis Family Asteroids with WISE/NEOWISE Observations
• Optical spectropolarimetry of large C-complex asteroids: polarimetric evidence for heterogeneous surface compositions
• Thermal evolution model from cometary nuclei to asteroids considering contraction associated with ice sublimation