Ceres, also designated 1 Ceres (see minor planet names), is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. It was discovered on January 1, 1801, by Giuseppe Piazzi, and is named after the Roman goddess Ceres—the goddess of growing plants, the harvest, and of motherly love.

With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt, and contains approximately a third of the belt's total mass. Recent observations have revealed that it is spherical, unlike the irregular shapes of smaller bodies with lower gravity. The surface of Ceres is probably made of a mixture of water ice and various hydrated minerals like carbonates and clays. Ceres appears to be differentiated into a rocky core and ice mantle. It may harbour an ocean of liquid water, which makes it a target of current searches for extraterrestrial life. Ceres may be surrounded by a tenuous atmosphere containing water vapour.

Ceres' apparent magnitude ranges from 6.7 to 9.3, hence at its brightest is still too dim to be seen with the naked eye. On September 27, 2007, NASA launched the Dawn Mission space probe to explore Vesta (2011-2012) and Ceres (2015).

Discovery

The idea that an unknown planet could exist between the orbits of Mars and Jupiter was first suggested by Johann Elert Bode in 1768. His considerations were based on the so called Titius-Bode law, a now-abandoned theory which had been proposed by Johann Daniel Titius in 1766. According to this law the semi-major axis of the planet should be near 2.8 AU. William Herschel's discovery of Uranus in 1781 increased faith in the law of Titius and Bode, and in 1800, twenty-four experienced astronomers combined their efforts and began a methodical search for the proposed planet. The group was headed by Franz Xaver von Zach. While they did not discover Ceres, they later found several large asteroids.

Piazzi's Book "Della scoperta del nuovo pianeta Cerere Ferdinandea" outlining the discovery of Ceres

Ceres was discovered on 1 January 1801, by Giuseppe Piazzi, who was searching for a star listed by Francis Wollaston as Mayer 87 because it was not in Mayer's zodiacal catalogue in the position given. Instead of a star, Piazzi found a moving star-like object, which he first thought was a comet. Piazzi observed Ceres a total of 24 times, the final time on February 11, when illness interrupted his observations. He announced his discovery on January 24, 1801 in letters to fellow astronomers, among them his compatriot Barnaba Oriani of Milan. He reported it as a comet but "since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and Lalande in Paris. The information was published in the September 1801 issue of the Monatliche Correspondenz.

Soon after this, Ceres' apparent position had changed (mostly due to the Earth's orbital motion). It then appeared too close to the Sun's glare, so other astronomers could not confirm the observations of Piazzi until the end of the year. However after such a long time it was difficult to predict its exact position. To recover Ceres Carl Friedrich Gauss, then only 24 years old, developed an efficient method of orbit determination. In only a few weeks, he predicted its path, and sent his results to Franz Xaver, Baron von Zach, the editor of the Monatliche Correspondenz. On December 31, 1801, von Zach and Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it.

SOURCE: Wikipedia