Dione

Ceres is the largest object in the asteroid belt and the smallest recognized dwarf planet. NASA’s Dawn mission showed that its brightest spots are salt deposits left by briny water rising from below, showing that Ceres is a water-rich world with a geologically recent past.

Object class

Dwarf planet

Mass

~0.00016 Earth masses

Host

Sun

Estimated age

~4.56 billion years

Composition

Rock and water ice

Temperature

~167 K mean surface

Makemake is a bright dwarf planet in the Kuiper Belt with methane and ethane ice on its surface. Hubble found a small, dark moon called MK2 in 2015; measuring that moon’s orbit could improve estimates of Makemake’s mass.

Object class

Dwarf planet

Mass

~0.00045 Earth masses

Host

Sun

Estimated age

~4.5 billion years

Composition

Rock, methane and ethane ice

Iapetus is Saturn's third-largest moon and one of its strangest, with a bright trailing hemisphere and a dark leading hemisphere. It also has a slow 79-day rotation, a distant orbit, and a giant ridge along much of its equator.

Object class

Icy moon

Host

Saturn

Composition

Water ice and rock with dark carbon-rich surface material