Ceres (dwarf planet)
With a diameter of about 950 km, Ceres is by far the largest and most massive object in the asteroid belt, and has about a third of the belt's total mass. It was once thought to be smaller than Vesta, which is brighter.  The asteroid is spherical, unlike the irregular shapes of smaller bodies with lower gravity. At its brightest it is still too dim to be seen with the naked eye. Ceres is located at 2.8 AU (257 million miles) from the Sun, which makes it the closest dwarf planet to the Sun. It is also the only dwarf planet in the Solar System than has no moons.