The Small Satellites of the Solar System: Priorities for the Decadal Study

Abstract

The small satellites are a diverse group of objects offering insights into the early formation of the Solar System and its collisional history. They can be subdivided into several groups: small inner moons, outer irregular moons, Martian moons, moons of asteroids, and moons of Centaurs/KBOs/TNOs. Many of these objects, especially the irregulars or their progenitors, are thought to be captured asteroids or Kuiper Belt Objects: a spacecraft mission that included them as targets would thus yield information on an object that came from elsewhere in the Solar System. Objects originating from the same reservoir as the irregular satellites may have brought both pre-biotic material and volatiles such as water to the inner Solar System. Flagship and New Frontiers class missions should plan trajectories and arrival times to capture spectroscopic and imaging observations of small satellites. It is also important to support ground-based and Earth-orbiting observations of these objects, laboratory measurements of candidate surface materials, and curation facilities for organic materials and ice- and gas-based materials. We place a high priority on a robust participating scientist program for JAXA's MMX mission to Phobos and Deimos, as a similar mission was our highest priority New Frontiers class mission in the last Decadal Survey. A sample returned by this mission would include material from a primitive object and possibly the Martian surface.