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Project Progress

We have completed the first part of the project, namely the initial parameter study of ice survival, under the surface of objects akin to known MBCs. In this study we investigate water ice longevity in the interior of small objects in the asteroid belt. We considered bodies of 0.15 to 2.5 km in radius (following the population of identified MBCs), composed of water ice and dust (in abundances common for comets and estimated for C-type asteroids). We also adopt two different density values (deduced from observations of Jupiter-family comets and C-type asteroids) and two limiting cases of heliocentric distances, following the known orbital distributions of C-type asteroids and MBCs.

We find that large bodies (up to a few km in diameter) may retain ice over the age of the Solar System even at shallow depths of the order of 50 m. Smaller bodies in the inner belt, on the other hand, may lose their ices. Members of Collisional families, which may be much younger (as is likely for the currently observed objects), are more likely to have ice at depths as shallow as 10-20 m, accessible to activation by collisions.

The issue of actual activation by such collisions, due to a population of small impactors, is under cur-rent investigation. We have compiled a reasonable representation of such an impactor population (constrained by existing observations of the small asteroid population) and are in the process of estimating its effect. This is achieved by applying several impact scaling laws to a suite of impact configurations, which parameterize both the impactor and the impacted surface. Our next step will be to derive the relation between the impact depths (or mass loss volumes) and the rate at which these depths can become accessible, due to the size distribution of impactor bodies.