Miranda

Enceladus is a small icy moon of Saturn whose south polar fractures spray water vapor and ice particles into space. Cassini connected those plumes to a global salty ocean beneath the crust, making Enceladus one of the Solar System's clearest ocean-world targets.

Object class

Icy ocean moon

Mass

~0.000018 Earth masses

Host

Saturn

Estimated age

~4.5 billion years

Composition

Water ice, silicate rock, global salty ocean

Temperature

~72 K surface

Proteus is Neptune's largest inner moon, a dark irregular body discovered by Voyager 2 in 1989. It keeps a box-like shape near the threshold where gravity would round it out, while its battered dark surface shows no clear sign of geological remodeling.

Object class

Small inner moon

Host

Neptune

10 Hygiea is the fourth-largest object in the asteroid belt. VLT observations published in 2019 showed it to be nearly spherical, suggesting that it could meet the physical roundness criterion for dwarf-planet status; it remains a dwarf-planet candidate.

Object class

Dwarf-planet candidate

Mass

~84 quadrillion metric tons

Estimated age

~4.5 billion years

Composition

Carbonaceous rock and ice