Ceres (dwarf planet)
Ceres or - in the nomenclature for asteroids - (1 ) Ceres is a dwarf planet and with an equatorial diameter of 975 km, the largest object in the main asteroid belt. It has no known moon. Ceres was discovered on 1 January 1801 by Giuseppe Piazzi was the first minor planet was long considered asteroid and is included in the group of dwarf planet since 2006. It is named after the Roman goddess of agriculture. Your astronomical symbol is a stylized sickle.
Even Johannes Kepler conjectured in the "gap" between the orbits of Mars and Jupiter, a planet, and the discovery of the Titius - Bode series 1770 confirmed such suspicions. Founded by the astronomer Franz Xaver von Zach and Johann Hieronymus Schroeter " Himmelspolizey " therefore went from 1800 specifically on the search for the suspected planet. For this purpose, the area around the ecliptic into 24 sections was divided. Each of these sections has been assigned to an observatory, which should keep searching him after the planet. Piazzi, who held the first object to be a comet, its discovery, however, succeeded by accident while checking a star catalog in the New Year's Eve 1801.
After Piazzi soon lost the new celestial body due to disease back from the eyes, succeeded Carl Friedrich Gauss by using its newly developed method for orbit determination, but to make a good prediction for the position of the dwarf planet. This was by Zach Ceres on December 7, 1801 find. Gauss's calculations proved to be immensely fruitful way for almost all branches of science, as he had first applied the method of least squares to the compensation bill for them. As it turned out, to Ceres actually moves between Mars and Jupiter, exactly where predicted by the Titius - Bode - row distance to the sun. Ceres was therefore - as the discovered Uranus in 1781 - considered a planet, bringing the number of planets in the solar system initially increased to eight. Only when the number of the celestial bodies found between Mars and Jupiter in 1850 increased rapidly, uphold these objects, the terms " Tiny Planets ", " minor planet ", " planetoid " or " asteroids " by, which also Ceres lost its status as a planet. A new version of the planet concept by the IAU, which was necessary due to the discovery of additional celestial bodies in the size class of Pluto, meant that Ceres is now classified together with Pluto, ( 136199 ) Eris ( 136472 ) Makemake and ( 136 108 ) Haumea as a dwarf planet.
Piazzi named it he discovered celestial bodies Ceres first Ferdinandea, after Ceres, the Roman goddess of agriculture and saint of the island of Sicily, and in honor of King Ferdinand IV of Naples, who had fled to Palermo in 1798. ( Was then for the third asteroid ( 3) Juno, taken up ) In Germany Johann Elert Bode suggested the name Juno before; for a short time also the name of Hera was in use ( which was awarded later on (103 ) Hera ). From Zach but made clear that " Prof. Piazzi has now baptized his own child, [ ... ] which he apparently was the first discoverer has the right ". As the ceremony of King Ferdinand but encountered in other nations on resistors, this part of the name was dropped soon.
In 1803, two years after the discovery of Ceres, the chemical element Cerium was discovered and named after this asteroid.
Ceres moves on an ellipse in the middle of the asteroid belt, at an average distance of 2.77 AU in 1682 days around the sun. The perihelion distance is 2.54 AU, the Apheldistanz 2.99 AE. The orbit is inclined by 10.6 ° to the ecliptic, the orbital eccentricity is 0.080.
The synodic period of Ceres is located at 467 days. While the opposition is removed between 1.59 AU and 2.00 AU from the Earth, reaching an apparent magnitude of up to 6.6 mag. Ceres therefore can already find with binoculars or a small telescope.
Size and mass
Ceres is the largest and most massive object in the asteroid belt in the inner solar system. For the mass, a value of 9.35 × 1020 kg is indicated, which corresponds to the 6390th part of Earth's mass. Ceres has thus about 3.5 times the mass of the heaviest asteroid ( 4) Vesta, and unites about 30 % of the total mass of the asteroid belt in itself.
Observations with the Hubble Space Telescope have shown that Ceres is an oblate spheroid, a slightly, with an equatorial diameter of 975 ( ± 3) km and a polar diameter of 909 ( ± 3) km. The surface of Ceres is thus about 2.85 million km ², that is slightly larger than the land area of Argentina. The rotation period is 9.075 hours, the average density is given as 2.077 ± 0.036 g/cm3.
Ceres has a dark carbon-rich surface with an albedo of 0.09. Radar observations have shown that the entire surface appears to be uniformly covered with powdery regolith. Outstanding or isolated surface features were observed only in 2001 after observations with the Hubble Space Telescope: There was a dark spot with a diameter of about 250 km, which was named in honor of the discoverer of Ceres " Piazzi ". Further observations with Hubble in 2003 and 2004 enabled the creation of a card next to " Piazzi " and an eye-catching, bright spot with around 400 km in diameter numerous smaller surface features shows, whose origin is still unknown.
The measurements of the Hubble Space Telescope also allow conclusions about the composition of Ceres: It is assumed that there is a differentiated dwarf planet with a rocky core and a mantle and a crust of lighter minerals and water ice. The differentiation is probably due to the released during the radioactive decay of aluminum isotope 26Al heat, which already mantle is likely to have formed from liquid water in the early days of the solar system. However, the outer ten kilometers melted not, but formed a solid crust of ice, while heavy material ( silicates, metals) collected in the core. Overall, Ceres should consist of 17 to 27 weight percent water. The amount of water on Ceres is estimated to be about five times the existing on Earth 's freshwater reserves. Moreover, it was demonstrated using the ESA Infrared Space Telescope Herschel steam to Ceres. The water discharge is 6 kg / s It is released from two locations on the surface. If Ceres is on its slightly elliptical orbit near the sun, the release is highest.
Despite the planets of similar construction was not a real planet of Ceres. Probably prevented the strong gravity of the adjacent Jupiter that Ceres could accumulate enough mass to evolve from a planetesimal to a large planet.
The Dawn spacecraft is expected to reach in February 2015 Ceres, swivel into orbit and the dwarf planet then explore several months. It is hoped that this mission more information about the structure and development of Ceres.
From 15 July 2011 to 5 September 2012, Dawn was already in orbit around the asteroid Vesta. Therefore, a comparison between the icy Ceres and the rocky Vesta will be possible.