• Scheeres, Daniel J.
• Sanchez, Paul

Abstract

The presence of small amounts of cohesive strength has been predicted and documented in rubble pile asteroids. Even cohesive strengths on the order of 10's of Pascals can have a dramatic effect on the failure conditions and behavior of granular material on asteroid surfaces. In this presentation we report on a new analytical theory for failure of an asteroid surface that accounts for cohesive strength. The theory assumes that the interior of the asteroid does not fail before the surface and is validated with detailed numerical simulations on a spherical, rotating body. The theory is expressed in terms of non-dimensional parameters and thus can be applied across a wide range of situations. Specifically, this theoretical understanding allows surface failure phenomenon to be predicted from fine regolith on small, rapidly spinning asteroids to meter-sized boulders on larger bodies with slower rotation rates. The theory identifies three distinct regimes of granular matter failure as a function of the relative strength of cohesion, as defined by the bond number (the ratio of cohesive strength to a granular particle's weight). For bond numbers less than unity, failure occurs via landslides in two ways. First, for low cohesion, landslides start at a fixed latitude defined by the granular material angle of friction. For larger bond numbers, but less than unity, the initial failure point transitions to higher latitudes and lies at the boundary between fission and landslide failure. For a bond number greater than unity, failure first occurs at the equator by the fission of material from the surface. When in this regime, particles that fail will in general be placed on hyperbolic orbits and immediately escape. This demarcates the beginning of the "disaggregation" phase of rubble pile asteroids and occurs for bodies < 300 m. It is also interesting to note that for any bond number, failure near the poles of a spinning body always occurs via landslides. The presentation will describe the theory and its main predictions, review the numerical confirmation of the approach and present a number of implications for the interpretation of in situ observations of asteroids. This work is supported by NASA grant 80NSSC18K0491....

Topics

• impedance spectroscopy
• surface
• phase
• theory
• simulation
• laser emission spectroscopy
• strength
• spinning