Interiors of Small Bodies: Foundations and Perspectives

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 the foundations for our current knowledge of small body interiors 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, substantially fractured (but not reorganized) interiors, and intact monolith-like bodies? We also seek to describe the prospects and requirements for answering these questions on a timescale of a decade or more. We note the motivation for finding these answers is both scientific and pragmatic, as understanding the interior properties of small bodies is essential for considering impact mitigation.