Ceres is a dwarf planet, the only one in the inner solar system. It’s in the asteroid belt between Mars and Jupiter, just close enough to sometimes be seen with the naked eye on a very dark night. Of course, even if you can’t see it you can learn some cool facts about it, so here’s a guided tour of Ceres.
Mass: 9.39×1020 kg
Equatorial Diameter: 946km
Equatorial Circumference: 2,992.1km
Known Moons: None
Orbit Period: 4.60 years
Surface Temperature: -38°C
How big is Ceres compared to Earth?
It’s pretty small. Ceres has a radius just 1/14th of Earth’s, and only 0.015% of the mass. Even the Moon is many times larger. Ceres is the smallest of the known dwarf planets, far too small for its gravity to hold on to an atmosphere. However it is large enough to have been forced into a spherical shape by its own weight.
Ceres is the largest object in the asteroid belt, by a long way. It’s believed to contain about a third of the total mass of the belt. Overall it’s the 33rd largest known object in the solar system.
How far is Ceres from the Sun?
Ceres has a slightly eccentric orbit, so its distance from the Sun varies. At its closest it’s 2.544 AU ( 380,576,983km) away; at its furthest that increases to 2.987 AU (446,848,839km).
Can you see Ceres from Earth?
Ceres is small and not very bright, so you can’t usually see it without a telescope. When it’s closer to Earth it does become more visible, though, and can be picked up in binoculars.
At its closest point of approach it’s just bright enough that you might see it with the naked eye, if it’s a very dark night and you know exactly where to look. It can almost always be seen with a telescope, even a small and inexpensive one.
When was Ceres discovered?
Giuseppe Piazzi, an astronomer from Palermo in Sicily, spotted Ceres in 1801. At first it was classed as a planet – many astronomers at the time believed there was another planet between Mars and Jupiter, and it was soon obvious that Ceres followed a planet-like orbit.
Then more objects, also orbiting the Sun, were discovered near it. These were given the name “asteroid”, meaning “star-like”, because even through a telescope they were just points of light. Therefore Ceres was the first asteroid to be discovered.
In 2006, when the category of dwarf planets was created, Ceres became one because it’s large enough to be roughly spherical. It’s still classed as an asteroid too, though.
Ceres has a lot of water
No spacecraft has landed on Ceres but NASA’s Dawn probe is now orbiting it, and has sent back a lot of data. The surface of the dwarf planet seems to be clay and carbonates. Underneath that is a layer of water ice about 100km thick, then a solid rocky core.
Some astronomers believe there could still be a subsurface ocean of liquid water on Ceres. There’s an atmosphere, made up mainly of water vapour, but it’s very thin. The surface is also quite chilly. It’s warm by asteroid standards at around -38°C, but that still isn’t very comfortable.
Ceres also has a lot of craters
There’s another reason the surface of Ceres isn’t very hospitable – it’s suffered a lot of impacts. Its surface is almost completely covered in craters. The atmosphere is too thin to have any real weather, so craters last a long time – some of them are probably billions of years old.
Does life exist on Ceres?
The Dawn probe has found traces of water on the surface, as well as salt deposits that were probably caused by water flooding out from the interior. That means there was a subsurface ocean on the planet in the past, and there could still be liquid water under the thick ice mantle. If there is water, with salts dissolved in it, life could have developed there.
More interesting Ceres facts
- Gravity on Ceres is very weak – only 2.9% of Earth’s. If you weigh 150 pounds (68kg) here you would only weigh 4.35 pounds (2kg) on Ceres.
- Ceres probably has more fresh water than Earth.
- Ceres has about the same land area as India.
- The name Ceres comes from the Roman goddess of agriculture.