January 01 – Discovery of Dwarf Planet Ceres (1801)

Happy New Year.

I couldn’t have planned it better myself. We start the New Year with 1 Ceres, the first asteroid to be discovered. Now designated a dwarf planet, Ceres was found by Giuseppe Piazzi on January 1st 1801, and announced to astronomers on January 24th, when he had made enough observations to be fairly sure of what it was. Its existence had been suggested by Johann Elert Bode in 1772, and the space where a planet ought to be was first mentioned by Kepler as long ago as 1597.

Ceres from the DAWN spacecraft (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Ceres from the DAWN spacecraft (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Ceres is enormous when compared to most of the other members of the main asteroid belt, measuring nearly 1000 km in diameter at the equator (about 60 km less if you measure through the poles), and accounts for about a third of the total mass of the belt. Despite this, Ceres is still too faint to be seen with the unaided eye.

Ceres is thought to be composed of a rocky core and icy mantle. Studies of the surface composition have tended toward the view of water ice, carbonates and iron-rich clays. It may also have a thin atmosphere.

The spacecraft DAWN has taken some great close-up shots of Ceres, including the following, taken on December 10th, 2015, from about 240 miles up (385 km) showing the area around a chain of craters, the Gerber Catena, in the southern hemisphere.

Ceres: the area around Gerber Catena (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Ceres: the area around Gerber Catena (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Another recent shot shows the impressive crater Occator, a feature about 60 miles (90 km) across, taken from much further out (about 2,700 miles (4,400 km). Don’t worry about the colours; Ceres isn’t blue. The colour scheme is a device for studying surface composition. Occator contains one of the five brightest areas spotted on Ceres.

Occator, Ceres, from DAWN (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Occator, Ceres, from DAWN (image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

The Roman deity Occator was god of the harrow (what you use to break up soil). He was heavily associated with Ceres, with good reason, because in Roman mythology the goddess Ceres was their equivalent of the Greek deity, Demeter, goddess of agriculture and grain crops (her name is almost certainly derived from the same root as the word “cereal”). Ceres was considered important enough to have a seven day festival in her honour each April, called the cerealia, including theatrical performances and a horse race in the Circus Maximus. On a slightly less savory note, a nighttime ritual of the cerealia involved tying lighted torches to the tails of foxes and releasing them into the Circus Maximus.

Ceres
Ceres

Today’s non-astronomical photograph is of a sculpture in the garden of the Schönbrunn Palace, Vienna, former residence of Emperor Franz Joseph.