Ceres
What is Ceres?
Dwarf planets· Diameter 946 km. The only dwarf planet in the asteroid belt, hiding traces of a briny subsurface ocean — small, but a serious astrobiology target.
The orbit of Ceres at this moment: https://nowsky.org/solar/orbit?fw=ceres&sp=6.5 — replayed live, no login.
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.
Frequently asked
- How big is Ceres?
- 946 km.
- How far is Ceres from Earth?
- 2.77 AU.
- What is notable about Ceres?
- 1/3 of the belt mass.
Ahuna Mons, an ice volcano built of brine
Ceres has a lone mountain, Ahuna Mons, 4 km high with a 20 km base. With no other peaks nearby and young, smooth flanks, Dawn's data identified it as a cryovolcano. Where Earth's volcanoes erupt molten rock, Ceres's pushed up a slurry of brine and mud that then froze in place. Its age, around 200 million years, means Ceres was geologically active until recently.
Ceres's other cryovolcanoes have already slumped to faint traces: ice is softer than rock, and over hundreds of millions of years a mountain of it spreads flat under its own weight. Ahuna still stands because it is the youngest, and beneath it there is thought to be a brine reservoir like the one that made the bright spots in Occator crater. That a dwarf planet 946 km across could have ice volcanoes was not anticipated before Dawn arrived.
The dwarf planet in depth
Ceres contains a third of the asteroid belt's entire mass by itself and is the belt's only dwarf planet. At its 1801 discovery it was hailed as a planet and spent half a century in textbooks as one — enduring Pluto's fate long before Pluto.
The Dawn spacecraft, orbiting from 2015, revealed a world of ice and salt. The dazzling bright spots in Occator crater are sodium-carbonate residue from subsurface brine — meaning Ceres has, or had, an underground ocean.
It circles at 2.77 AU between Mars and Jupiter every 4.6 years; find it mid-belt in the orbit view.
Ceres's shifting status is the history of planet classification itself: a full planet for half a century after its 1801 discovery, demoted to asteroid as similar bodies piled up, then reclassified a dwarf planet alongside Pluto in 2006. Today, hints of a briny reservoir underground are promoting it once more — into the asteroid belt's most serious astrobiology target.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.