Ceres
What is Ceres?
Dwarf planets· Diameter 946 km. The only dwarf planet in the asteroid belt between Mars and Jupiter. Salty water may still lie beneath its surface, which makes it a focus of scientific interest.
Orbit and size
| Diameter | 946 km |
|---|---|
| Distance | 2.77 AU |
| Region | Asteroid belt |
| Note | 1/3 of the belt mass |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Ahuna Mons, the lonely ice volcano of Ceres
Ceres has a lone mountain, Ahuna Mons, with no other peaks around it. It stands about 4 km high on average and about 20 km wide at the base. Its smooth, bright-streaked slopes led scientists using Dawn's data to identify it as an ice volcano. Volcanoes on Earth erupt melted rock; this one pushed up a paste of ice mixed with salty mud.
Crater counts show that Ahuna Mons formed within the last few hundred million years, very recent for a solar system about 4.6 billion years old. Its bright streaks contain salts such as sodium carbonate, the same kind of material as the white spots in Occator crater. Before Dawn arrived, no one expected to find an ice volcano on a body only 946 km across.
After discovering Ceres, Piazzi followed it for six weeks before illness stopped his work, and meanwhile Ceres was lost in the Sun's glare. The 24-year-old mathematician Carl Gauss then invented a new way to calculate an orbit from so few observations. On 31 December 1801 the astronomer von Zach found Ceres again at the spot Gauss had predicted.
The dwarf planet in depth
Ceres was discovered on 1 January 1801 by Giuseppe Piazzi, an astronomer in Sicily. At 946 km across it is the largest body in the asteroid belt, and on its own it holds a third of the belt's total mass. It orbits 2.77 AU from the Sun, taking 4.6 years per lap. One AU is the distance from the Earth to the Sun, so Ceres circles 2.77 times farther out than we do.
Ceres was first called a planet. But as more small bodies were found on similar orbits, it was reclassified as an asteroid around the 1850s. In 2006 it joined Pluto in the new category of dwarf planets. The way its label has changed shows how people's idea of a planet has changed.
In 2015 the Dawn spacecraft went into orbit around Ceres and studied it for more than three years. Its biggest find was a set of dazzling white spots in Occator crater. They turned out to be sodium carbonate, a kind of salt. Salty water had seeped up from below; the water escaped into space and the salt stayed behind. This means a layer of salty water may still exist underground.
Frequently asked
- How big is Ceres?
- The diameter of Ceres is 946 km.
- How far is Ceres from Earth?
- The distance of Ceres is 2.77 AU.
- What is notable about Ceres?
- The note of Ceres is 1/3 of the belt mass.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.