In addition to the five mission concepts listed above, for the 5th New Frontiers mission, the 2013 Planetary Science Decadal Survey committee identified two additional candidates that will be added to the list.[3]

Io Observer

The focus of this mission is to determine the internal structure of Io and to investigate the mechanisms that contribute to the satellite’s intense volcanic activity from a highly elliptical orbit around Jupiter, making multiple flybys of Io. This mission depends on sufficient advances in system power and radiation protection.[5]

Lunar Geophysical Network

This mission consists of several identical landers distributed across the lunar surface, each carrying geophysical instrumentation. The primary science objectives are to characterize the Moon’s internal structure, seismic activity, global heat flow budget, bulk composition, and magnetic field. It would expand the instruments left on the surface on the moon left by Apollo program missions to include coverage of the far side of the moon as well.[5]