Accepted for publication in Planetary and Space Science. February, 2003. For preprint information please contact the first author. 

 

ABSTRACT 

With the surface properties and shapes of solar system small bodies 

(comets and asteroids) now being routinely revealed by spacecraft and 

Earth-based radar, understanding their interior structure represents the 

next frontier in our exploration of these worlds. Principal unknowns include 

the complex interactions between material strength and gravity in 

environments that are dominated by collisions and thermal processes. Our 

purpose for this review is to use our current knowledge of small body 

interiors as a foundation to define the science questions which motivate 

their continued study: In which bodies do “planetary” processes occur? 

Which bodies are “accretion survivors”, i.e. bodies whose current form and 

internal structure are not substantially altered from the time of formation? 

At what characteristic sizes are we most likely to find “rubble piles”, i.e. 

substantially fractured (but not reorganized) interiors, and intact monolithlike 

bodies? From afar, precise determinations of newly discovered 

satellite orbits provide the best prospect for yielding masses from which 

densities may be inferred for a diverse range of near-Earth, main-belt, 

Trojan, and Kuiper belt objects. Through digital modeling of collision 

outcomes, bodies that are the most thoroughly fractured (and weak in the 

sense of having almost zero tensile strength) may be the strongest in the 

sense of being able to survive against disruptive collisions. Thoroughly 

fractured bodies may be found at almost any size, and because of their 

apparent resistance to disruptive collisions, may be the most commonly 

found interior state for small bodies in the solar system today. Advances in 

the precise tracking of spacecraft are giving promise to high order 

measurements of the gravity fields determined by rendezvous missions. 

Solving these gravity fields for uniquely revealing internal structure requires 

active experiments, a major new direction for technological advancement in 

the coming decade. We note the motivation for understanding the interior 

properties of small bodies is both scientific and pragmatic, as such 

knowledge is also essential for considering impact mitigation.