Ceres (dwarf planet)
| Discovery | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Discovered by | Giuseppe Piazzi | ||||||||
| Discovery date | 1 January 1801 | ||||||||
| Designations | |||||||||
| 1 Ceres | |||||||||
| Pronunciation | /ˈsɪəriːz/, SEER-eez | ||||||||
Named after | Cerēs | ||||||||
| Adjectives | Cererian, -ean (/sɪˈrɪəriən/) | ||||||||
| Symbol | |||||||||
| Orbital characteristics | |||||||||
| Epoch 21 January 2022 (JD 2459600.5) | |||||||||
| Aphelion | 2.98 AU (446 million km) | ||||||||
| Perihelion | 2.55 AU (381 million km) | ||||||||
| 2.77 AU (414 million km) | |||||||||
| Eccentricity | 0.0785 | ||||||||
| |||||||||
Average orbital speed | 17.9 km/s | ||||||||
| 291.4° | |||||||||
| Inclination |
| ||||||||
| 80.3° | |||||||||
| 7 December 2022 | |||||||||
| 73.6° | |||||||||
| Satellites | Dawn (derelict space probe) | ||||||||
| Proper orbital elements | |||||||||
Proper semi-major axis | 2.77 AU | ||||||||
Proper eccentricity | 0.116 | ||||||||
Proper inclination | 9.65° | ||||||||
Proper mean motion | 78.2 deg / yr | ||||||||
Proper orbital period | 4.60358 yr (1681.458 d) | ||||||||
Precession of perihelion | 54.1 arcsec / yr | ||||||||
Precession of the ascending node | −59.2 arcsec / yr | ||||||||
| Physical characteristics | |||||||||
| Dimensions | (966.2 × 962.0 × 891.8) ± 0.2 km | ||||||||
| 469.7±0.1 km (291.9 mi) | |||||||||
| 2,772,368 km2 | |||||||||
| Volume | 434,000,000 km3 | ||||||||
| Mass | |||||||||
Mean density | 2.1616±0.0025 g/cm3 | ||||||||
Equatorial surface gravity | 0.284 m/s2 (0.0290 g0) | ||||||||
| 0.36±0.15 (estimate) | |||||||||
Equatorial escape velocity | 0.516 km/s 1141 mph | ||||||||
| 9.074170±0.000001 h | |||||||||
Equatorial rotation velocity | 92.61 m/s | ||||||||
| ≈4° | |||||||||
North pole right ascension | 291.42744° | ||||||||
North pole declination | 66.76033° | ||||||||
| 0.090±0.0033 (V-band) | |||||||||
| |||||||||
| C | |||||||||
| |||||||||
| 3.35 | |||||||||
| 0.854″ to 0.339″ | |||||||||
Ceres (minor-planet designation: 1 Ceres) is a dwarf planet in the main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid, discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily, and announced as a new planet. Ceres was later classified as an asteroid and more recently as a dwarf planet, the only one not beyond the orbit of Neptune and the largest that does not have a moon.
Ceres's diameter is about a quarter that of the Moon. Its small size means that even at its brightest it is too dim to be seen by the naked eye, except under extremely dark skies. Its apparent magnitude ranges from 6.7 to 9.3, peaking at opposition (when it is closest to Earth) once every 15- to 16-month synodic period. As a result, its surface features are barely visible even with the most powerful telescopes, and little was known about it until the robotic NASA spacecraft Dawn approached Ceres for its orbital mission in 2015.
Dawn found Ceres's surface to be a mixture of water, ice, and hydrated minerals such as carbonates and clay. Gravity data suggest Ceres to be partially differentiated into a muddy (ice–rock) mantle/core and a less dense, but stronger crust that is at most thirty percent ice by volume. Although Ceres likely has an internal ocean of liquid water, brines still flow through the outer mantle and reach the surface, allowing cryovolcanoes such as Ahuna Mons to form roughly every fifty million years. This makes Ceres the closest known cryovolcanically active body to the Sun. Ceres has an extremely tenuous and transient atmosphere of water vapour, vented from localised sources on its surface.