When we think about dwarf planets, the first one that comes to mind is Pluto.  Following that, we think about Makemake, Eris, Haumea, and Ceres.  We get this mental image of Pluto, followed by a cluster of little planets out in the Kuiper Belt.  That mental diagram is wrong for many reasons, but it’s mostly wrong because of Ceres.  Ceres is not in a cluster out in the Kuiper Belt; it’s in our own back yard.

From NASA, comparison of the Earth, Moon, and Ceres

Ceres, the largest object within the Asteroid Belt, is the only dwarf planet in the inner solar system.  Discovered by Giuseppe Piazzi on January 1st, 1801, Piazzi thought at first that he had found a comet.  After watching it for a while, Piazzi announced his discovery January 24th.  He did note that the “comet” was moving in such a slow and uniform manner that it might be something more interesting.  Indeed it was.

Ceres is named for the Roman goddess of the harvest, and was called “Hera” for a while in Germany, and “Demeter” in Greece.  Its astronomical symbol is the sickle – that looks like the universal symbol for “female” with a chunk missing from it in the 6:00 to 9:00 position.  Remember, the astronomical symbol for Venus is the female symbol.

NASA/ESA HST, images of Ceres - nature of the white spot unknown

For a long time Ceres was listed as a planet, along with 2 Pallas, 3 Juno, and 4 Vesta.  Its final designation, that of a dwarf planet, came about in 2006.  The largest object in the Asteroid Belt, Ceres is responsible for a full third of its mass.  Mostly spherical, its surface is probably a mixture of water ices and gooey carbonates and clays.

Modern observation has shown that Ceres appears to have differentiated into a rocky core with an icy mantle.  There may even be a sub-surface ocean of liquid water.  The Dawn space probe will visit Ceres in 2015.  That should prove exciting, so mark it on your calendars; only four more years to go!  It’s been estimated that Ceres contains more fresh frozen water than what we find on Earth.

NASA/ESA, A. Field - possible layers of Ceres

There has been some talk that Ceres may have captured biologically active ejecta from the young Earth, and with a warm, sub-surface (possibly salty) ocean, it could have been colonized.  While all discoveries of possible sub-surface liquid water leads to talk of extra-terrestrial life, Ceres is definitely in a better position to study than, say, Europa.

Ceres is certainly an interesting object to study.  With exceptional viewing conditions, a very sharp-sighted person can see Ceres (very dimly), but it mostly requires some sort of viewing aid.  Ceres will next be at perihelion December 18, 2012, so get those binoculars ready.

NASA/ESA HST enhanced (to show detail) image of Ceres