1 Ceres: The Asteroid Belt's lone dwarf planet

By : John Whitworth / Updated : May 25th, 2026 10:18

Discovery and naming of Ceres

Normally, names and numbers are allocated to the asteroid by the Minor Planet Centre (M.P.C.), part of the Smithsonian Astrophysical Observatory (S.A.O.). Some asteroids, such as Ceres, were named before the S.A.O. took responsibility for assigning names and numbers. Some asteroids are dedicated by the discoverers to people or named after mythology, such as 2602 PatrickMoore (dedicated) and 15810 Arawn.

Those not named will be assigned the year it was discovered and letters. Usually, the asteroid is called Ceres without the number. The number ID of an asteroid usually indicates when it was discovered. For example, 1 Ceres is the first asteroid to be discovered, so it has the number 1.

Ceres was discovered by Italian astronomer Giuseppe Piazzi of the Palermo Observatory on January 1, 1801. Additional observations were not possible due to Giuseppe's ill health. It would be "rediscovered" exactly a year later by German Hungarian astronomer Franz von Zach, who used an orbit calculated by the German mathematician Carl Friedrich Gauss.

Ceres Facts

• Ceres is the largest asteroid in the asteroid belt. Ceres' mass is a quarter of all the asteroids in the zone. It has no Moon, nor does it have a ring system like Saturn. It was the first asteroid to be discovered.
• Ceres' name originates from the Roman Goddess of Corn and Harvest. The term Cereal also comes from the same origin. Although it has an 's' at the end, it is still in the singular voice.
• Although Ceres is the largest asteroid, it is not the brightest. The brightest by albedo is Vesta.
• Charon (604km), the largest of Pluto's moons, is larger than Ceres (476 km).

Atmosphere and hidden water ice

• There are signs of large amounts of water ice beneath the surface. Water ice could account for 25% of Ceres's total mass. It could be the most water-rich after the Earth in The Solar System. In addition to water ice, there is evidence of water vapour. In addition to the water ice, there is evidence of material originating from the outskirts of the Solar System. N.A.S.A.
• Ceres has a fragile atmosphere, but it has water, an important ingredient needed for life to exist. Although it does not have an atmosphere, there is water vapour on the planet, possibly caused by impact on the ice from small impacts with micro-meteors. N.A.S.A.
• Ceres's mass is estimated/calculated at 939,300 (10^15) kg.
• It takes 9.074 hours to do a full rotation period.
• Ceres absolute magnitude is 3.33, which is the object's brightness. A higher absolute magnitude means the object is faint, whereas a very low number means it is very bright.
• The albedo of the Ceres is 0.09. The albedo is the amount of radiation reflected into space by Ceres.
• Ceres's aphelion is 2.9773 A.U. which is the point in the orbit that is furthest from the thing (e.g. the Sun) that it is orbiting. At this point, it will then return to the orbit target. The perihelion of Ceres is 2.5577 A.U., the closest point it gets to the Sun. The mean anomaly of Ceres is 334.32719, the object's angular distance from the perihelion or aphelion. Ref: Dictionary.
• The Longitude of the Ascending Node of Ceres is 80.26642 degrees. It is the angle between the Reference Direction and the Ascending Node. It is generally represented by the Greek letter Ω. The ascending node is the point at which the object passes north. The descending node is the southern equivalent.
• The Argument of Perihelion of Ceres is 73.53162. It is the angle along the orbit of a planet or other Solar System object as measured from the ascending node (analogous to right ascension and longitude). Ref:Hawaii.
• The approximate diameter of Ceres is 960 x 932 km. The Mean Orbit Velocity (M.O.V.) is the speed at which it orbits, which is 1.00 km/h. The average distance of the object from its parent is 1.00km.

Dawn Probe

Even though it is nearer than the Gas Giants that inhabit our Solar System, it was not until 2015 that the Dawn probe went into orbit around Ceres, a dwarf planet. The Dawn probe had previously been to Vesta four years previously. The Dawn probe reinforced the view that dwarf planets could have hosted oceans for a significant part of their history, and they still do. The path to Ceres was not a direct route. Instead, the Dawn probe made several loops round N.A.S.A.

Dwarf Planet

Ceres was once seen as a planet but was eventually downgraded to an asteroid. In 2006, after the discovery of Eris, which at the time was thought to be bigger than Pluto, rules were created to define a planet. The IAU came up with the following rules that an object needed to pass to be a planet:-

Criteria for planet status

• Large enough to be spherical.
• Orbit a Star.
• Have cleared the way in front of it.

As Pluto had not cleared the way in front of it, it was demoted to Dwarf Planet status. As a result, Ceres was upgraded to dwarf planet status. There are four other dwarf planets in out Solar System, they are :-

• Haumea
• MakeMake
• Orcus
• Sedna

Ceres is the only dwarf planet that does not reside in the Kuiper Belt, an area of the Solar System past Neptune.

Ceres is the largest asteroid in either the asteroid belt or the Kuiper Belt. It was once classed as a planet because it was so large, but it has since been downgraded to an asteroid and then upgraded to a dwarf planet. It was the first asteroid to be discovered.

Orbital Details

Ceres orbital period, the time it takes to complete an orbit of the Sun, is 4.6 years. The orbital inclination of Ceres, the angle at which Ceres orbits the orbital plane, is 10.5868 degrees. The orbital eccentricity of Ceres is 0.0786358, the degree to which Ceres orbits close to a circular (0) orbit as opposed to an elliptical (1). The semi-major axis of Ceres' orbit is 2.7666191 (A.U.), the furthest point from the centre to the edge of an ellipse.

Ceres has not been classed as a Near Earth Object (NEO) asteroid as its path does not come close (proximity) or cross the orbital path of the Earth as it travels around the Sun.

Orbital Path

The object's path is under the ecliptic if the white lines are above. If the white lines are below, the path is above the ecliptic. The white lines indicate the Inclination of the object. The image was created using N.A.S.A. Solar System Dynamics.