Triggering the Activation of Main Belt Comets: The Effect of Porosity

TL;DR

This study investigates how porosity affects impact crater depth and ice exposure in Main Belt Comets, suggesting impacts can expose sub-surface ice within 15 meters, influencing comet activity models.

Contribution

It extends impact simulations to porous materials and accounts for impact-induced ice loss, providing new insights into MBC activation mechanisms.

Findings

Impact craters in porous MBCs reach about 15 meters deep.

Ice loss due to impact heat is negligible.

Multiple impact sites likely contribute to MBC activity.

Abstract

It has been suggested that the comet-like activity of Main Belt Comets is due to the sublimation of sub-surface water-ice that is exposed when these objects are impacted by meter-sized bodies. We recently examined this scenario and showed that such impacts can in fact excavate ice and present a plausible mechanism for triggering the activation of MBCs (Haghighipour et al. 2016). However, because the purpose of that study was to prove the concept and identify the most viable ice-longevity model, the porosity of the object and the loss of ice due to the heat of impact were ignored. In this paper, we extend our impact simulations to porous materials and account for the loss of ice due to an impact. We show that for a porous MBC, impact craters are deeper, reaching to approximately 15 m implying that if the activation of MBCs is due to the sublimation of sub-surface ice, this ice has to be within the top 15 m of the object. Results also indicate that the loss of ice due to the heat of impact is negligible, and the re-accretion of ejected ice is small. The latter suggests that the activities of current MBCs are most probably from multiple impact sites. Our study also indicates that in order for sublimation from multiple sites to account for the observed activity of the currently known MBCs, the water content of MBCs (and their parent asteroids) needs to be larger than the values traditionally considered in models of terrestrial planet formation.