Dwarf planet Ceres (1 Ceres)

Discovered by:                 Giuseppe Piazzi
Discovery date:                January 1, 1801     
Minor planet category:      Dwarf planet, Main belt
Magnitude range:              +6.6 to +9.3
Aphelion:                         2.9765 AU (445.28 million kms or 276.68 million miles)
Perihelion:                       2.5570 AU (382.52 million kms or 237.69 million miles)
Semi-major axis:              2.7668 AU (413.91 million kms or 257.19 million miles)

Equatorial radius:             487 kms or 303 miles
Polar radius:                    455 kms or 283 miles
Mass:                              9.43×10^20 kg or 0.00015 Earths
Mean density:                  2.08 g/cm3
Escape velocity:               0.51 km/s or 0.32 miles/s
Sidereal rotation period:     9.07 hours
Axial tilt:                          3 degrees

Eccentricity:                     0.075797
Orbital period:                   4.6 years
Inclination:                        10.6 degrees
Longitude of ascending node: 80.328 degrees
Albedo:                             0.09
Mean surface temp:          168 K (-105 C or -157 F)
Max. surface temp:           235 K (-38 C or -37 F)

Ceres as imaged by the Hubble Space Telescope (NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), and L. McFadden (University of Maryland, College Park))

Ceres was discovered on January 1, 1801 the first day of the 19th century. Ceres is located at an average distance of 2.77 AU (413.9 million kilometres or 257.2 million miles) from the Sun, in the main asteroid belt between the orbits of Mars and Jupiter.

It was suggested by Johann Elert Bode in 1772 that an undiscovered planet could exist between the orbits of Mars and Jupiter. This was based on a now discredited hypothesis proposed by Bode and Johann Daniel Titius in 1766. The theory known as Titius-Bode law, predicted to a reasonable accuracy the distances of the then known planets from the Sun, with one exception, a missing planet at a distance of 2.8 AU from the Sun.

Titius-Bode law (or sometime simply just Bodes law) once again fit well with the orbit of Ceres and was only discredited following the later discovery of Neptune, which didn't fit the pattern.

Originally classified as a planet (along with 2 Pallas, 3 Juno and 4 Vesta), it was 50 years later re-classified as an asteroid and then re-classified again on August 24, 2006 as a dwarf planet, the only one in the inner Solar System.

The other known dwarf planets are Eris, Haumea, Makemake and Pluto, all of which are located in the outer Solar System.

Ceres is a rocky body approx. 950 kilometres (590 miles) in diameter. It's the largest object in the asteroid belt but the smallest identified dwarf planet.

It contains about one-third of the mass of the asteroid belt.

The mass of Ceres comprises is about 3.0×10^20 kg, which is about 4% of the mass of the Moon.

The apparent magnitude of Ceres ranges from +6.7 to +9.3. Even at its brightest it's not visible to the naked eye but is an easy binocular object.

The surface of Ceres is probably a mixture of water ice and various hydrated minerals such as carbonates and clay minerals.

It's possible that Ceres may have a thin atmosphere with water frost on its surface.

The maximum temperature on the surface of Ceres is estimated to be 235 K (-38 C or -37 F). The average temperature is 168 K (-105 °C or -157 °F).

Orbital period is 4.6 years with the orbit inclined at 10.6 degrees. This compares to 1.58 degrees for the Earth, 7 degrees for Mercury and 17 degrees for Pluto. Orbital eccentricity is 0.08. This is very similar to 0.09 for Mars but much greater than 0.017 for the Earth (almost circular orbit).

NASA's unmanned Dawn spacecraft is currently en-route to Ceres and will arrive in March or April 2015. The spacecraft was previously in orbit around asteroid Vesta between July 2011 and September 2012.