Showing papers by "Paul Sánchez published in 2014"

The strength of regolith and rubble pile asteroids

Abstract: We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but non-zero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale-independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC3. One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders.

Constraints on the Physical Properties of Main Belt Comet P/2013 R3 from its Breakup Event

Abstract: Jewitt et al. (2014) recently reported that main belt comet P/2013 R3 experienced a breakup, probably due to rotational disruption, with its components separating on mutually hyperbolic orbits. We propose a technique for constraining physical properties of the proto-body, especially the initial spin period and cohesive strength, as a function of the body's estimated size and density. The breakup conditions are developed by combining mutual orbit dynamics of the smaller components and the failure condition of the proto-body. Given a proto-body with a bulk density ranging from 1000 kg/m3 to 1500 kg/m3 (a typical range of the bulk density of C-type asteroids), we obtain possible values of the cohesive strength (40 - 210 Pa) and the initial spin state (0.48 - 1.9 hr). From this result, we conclude that although the proto-body could have been a rubble pile, it was likely spinning beyond its gravitational binding limit and would have needed cohesive strength to hold itself together. Additional observations of P/2013 R3 will enable stronger constraints on this event, and the present technique will be able to give more precise estimates of its internal structure.

Contact Motion on Surface of Asteroid

Abstract: A comprehensive method for modeling the motion of a spherical pod at the surface of an asteroid is presented. Using triangular faceted surfaces, the largest features of the asteroid (global shape, monoliths, and large boulders) are modeled. The presence of smaller rocks is accounted for using a stochastic model of rock generation and collision. The contact dynamics on regolith or harder surfaces, including multiple contact points situations, are described. The force, torque, and coefficient of rolling resistance are introduced, explained, and estimated. Finally, this model is applied to a hypothetical deployment case on asteroid Itokawa. The numerical simulations show landing time around 5 h, with the main landing basin located in Muses Sea. It also proves the importance of each and every level of detail of the asteroid model for an accurate understanding of asteroid surface motion and the effective design of practical deployment strategies.