This picture of the asteroid Ceres was made by the Hubble Space
Telescope in December 2003 and January 2004. Ceres was declared
a "dwarf planet", along with Pluto and Eris, in 2006. Click on
image for full size Image courtesy of NASA, ESA, J. Parker
(Southwest Research Institute), P. Thomas (Cornell University),
L. McFadden (University of Maryland, College Park), and M.
Mutchler and Z. Levay (STScI). Ceres: Asteroid and Dwarf Planet
Ceres is the largest asteroid in the main asteroid belt. It was
classified as a "dwarf planet" in 2006, along with Pluto and
Eris. Ceres was discovered on January 1, 1801 by the Italian
astronomer and monk Giuseppe Piazzi. Ceres has a diameter of
about 975 km (605 miles). It is by far the largest and most
massive body in the main asteroid belt, and contains about a
third of the belt's total mass. Ceres orbits the Sun once every
4.6 years. Its orbit lies between the orbits of Mars and
Jupiter. The asteroid turns on its axis once every 9 hours, so
that's how long a day is on Ceres.