Ceres or – in the nomenclature for asteroids – (1) Ceres is a dwarf planet and with its equatorial diameter of 975 km, the largest object in the main asteroid belt. Ceres was discovered as the first minor planet by Giuseppe Piazzi on 1 January 1801. He was considered to be an asteroid for a long time and is now included to the group of dwarf planet since of 2006.
Even Johannes Kepler suspected in the “gap” between the orbits of Mars and Jupiter a planet, and the discovery of the Titius-Bode law in 1770 encouraged such an assumption. The by the astronomers Franz Xaver von Zach and Johann Hieronymus Schroeter founded “Skypolice” started to search for such a planet from 1800 on. Therefore the area around the ecliptic was divided into 24 sections. Each of these sections has been allocated an observatory that would scan for the planet. Piazzi, who in the beginning opined the object to be a comet, discovered Ceres by chance during the review of a star catalog in the New Year´s night 1801.
Piazzi fell sick and was not able to continue his observations. The celestial body moved further towards the sun and could not immediately be found again. Carl Friedrich Gauss succeeded by using a newly developed method for orbit determination, to make a good prediction of the dwarf planet´s position. So Franz Xaver von Zach Ceres was able to retrieve it on 7 December 1801. The technology developed by Gauss for this purpose turned out to be immensely fruitful, because it contained the famous method of least squares as a kind of by-product. As it turned out, Ceres actually moves between Mars and Jupiter in the by the Titius-Bode law predicted distance to the sun. Ceres was therefore, as the 1781 discovered Uranus, considered to be a planet, increasing the number of planets in the solar system to eight. Only when the number of celestial bodies found between Mars and Jupiter rised rapidly, the terms “Small Planet”, “minor planets”, “planetoids” or “asteroid” were used, and due to this 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 (136108) Haumea as a dwarf planet.
| Discovery date | 1801 (Giuseppe Piazzi) |
| Semi-major axis | 414 086 904 km = 4.140 x 108 km (2.768 AU) Comparison: 2.768 x Earth |
| Perihelion | 382 671 351 km = 3.826 x 108 km (2.558 AU) Comparison: 2.558 x Earth |
| Aphelion | 445 502 456 km = 4.455 x 108 km (2.978 AU) Comparison: 2.978 x Earth |
| Diameter | 975 km = 9.75 x 102 km Comparison: 0.0764329 x Earth |
| Mass | 935 000 000 000 000 000 000 kg = 9.35 x 1020 kg Comparison: 0.000156 x Earth |
| Density | 2.077 g/cm3 Comparison: 0.3766 x Earth |
| Escape velocity | 1836 km/h = 510.00 m/s Comparison: 0.0456 x Earth |
| Sidereal rotation period | 0.3788 Earth days 9.066 hours |
| Orbital period (Length of a year) |
1.278 Earth years 467 Earth days Comparison: 1.278 x Earth |
| Average orbital speed | 64 472 km/h = 17 909 m/s Comparison: 0.6013 x Earth |
| Eccentricity | 0.0796 Comparison: 4.766 x Earth |
| Inclination | 10.59° |
| Axial tilt | 4° Comparison: 0.170 x Earth |
| Minimum/Maximum surface temperature |
-106 °C = 167 K Comparison: The temperature of the earth is ~ 185/331 K |
| Composition of the atmosphere |
unknown Comparison: The atmosphere of the earth is mainly composed of N2 and O2. |
Moons:
Ceres has no moon.