Low-activity Main-belt Comet 133P/Elst-Pizarro: New Constraints on Its Albedo, Temperature, and Active Mechanism from a Thermophysical Perspective

摘要

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, ${p}_{{m{v}}}=0.074pm 0.013$, and mean Bond albedo ${A}_{mathrm{eff},{m{B}}}=0.024pm 0.004$.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 $sim 1.4imes {10}^{23},{{m{s}}}^{-1}$, being far weaker than $sim {10}^{26},{{m{s}}}^{-1}$ 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 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.