Ceres: The Dwarf Planet in the Asteroid Belt

Ceres at a glance

Giuseppe Piazzi spotted Ceres in 1801, and NASA says it was the first member of the asteroid belt to be identified. The belt lies between Mars and Jupiter. As of November 2026, Ceres is one of the five dwarf planets on NASA's list, a set explained in how many dwarf planets there are.

An AU, or astronomical unit, is the average distance from Earth to the Sun, about 150 million km (93 million miles). Sunlight takes about 22 minutes to reach Ceres, NASA says.

An asteroid and a dwarf planet at once

The International Astronomical Union (IAU) defines a dwarf planet as a body that orbits the Sun, is nearly round, has not cleared the neighborhood around its orbit, and is not a moon. Ceres meets every part of that. It circles the Sun, gravity has pulled it into a round shape, it shares the belt with other bodies, and it orbits no planet. The belt is also where asteroids live, and Ceres lives there too.

NASA's dwarf planet page says Ceres was once considered a planet and, for many years, an asteroid. It adds that Ceres is the only dwarf planet in the inner Solar System. So the two labels do not conflict. "Asteroid" describes where Ceres lives and what astronomers called it for generations. "Dwarf planet" is the category the IAU assigned in 2006. The rule behind that category is explained in what a dwarf planet is, and the region itself is covered in the asteroid belt.

The Dawn mission, 2007 to 2018

Dawn made extended stays at two worlds in the asteroid belt, Vesta and Ceres. It also became the first spacecraft to orbit a dwarf planet.

• 2007: Dawn launches on September 27.
• 2011: Dawn arrives at the giant asteroid Vesta on July 16, and it leaves on September 5, 2012.
• 2015: Dawn enters orbit around Ceres in March, about four months before New Horizons flew past Pluto.
• 2018: Dawn runs out of hydrazine propellant on October 31, and NASA declares the mission over on November 1.

NASA's pages give March 5 or March 6 for the Ceres arrival, so this article says only March 2015. The Pluto flyby that followed is covered in what New Horizons found at Pluto.

Hydrazine is the fuel Dawn used to control its pointing. Without it, the spacecraft could no longer aim its solar panels at the Sun or its antenna at Earth, and contact was lost. Dawn did not crash. NASA says it remains in orbit around Ceres, no longer operating, and will stay there for at least a couple of decades and probably much longer.

Occator Crater's bright spots

Dawn found more than 300 bright features, called faculae, on Ceres's dark landscape. The best known sit in Occator Crater, which is 92 km (57 miles) wide and formed about 20 million years ago, according to a 2020 NASA release.

The brightest area has the largest deposit of carbonate minerals ever seen outside Earth, NASA says. Carbonates are salts. The bright material is mostly sodium carbonate, and the central spot, Cerealia Facula, is also rich in sodium chloride bound with water and in ammonium chloride. A U.S. Geological Survey paper describes Cerealia as a dome and the neighboring Vinalia Faculae as a depression, each surrounded by patchy bright material.

Where did the salts come from? NASA's 2020 release says the bright areas come from salty water below. Dawn data point to a reservoir of brine, or very salty water, about 40 km (25 miles) down and hundreds of miles wide, and some of the bright regions are less than 2 million years old. The geological survey paper concludes that "brine fountaining" best explains the shapes. In that process, briny liquid is pushed out and freezes quickly into salt and ice particles. Dawn saw no active plumes, so eruptions probably happen less often than once every few years.

Ice, salts and possible liquid

NASA's facts page says Ceres may be up to 25 percent water. It has a rocky, dusty crust with large salt deposits, including magnesium sulfate. Layers of ice may lie just below the surface, and permanently shadowed craters could hold water ice for long periods.

Dawn's results suggest more. NASA's mission highlights say the outer shell is rich in water as ice and hydrates, which are minerals that contain water, and that some briny liquid may remain under the surface. Dawn also found ammonia and abundant organic material near Ernutet Crater, which the team thinks came from Ceres's interior. Ahuna Mons, a mountain about 5 km (3 miles) tall on its steepest side, is thought to be a cryovolcano, a volcano that erupts salty water and mud instead of molten rock. Its existence suggests liquid may still exist beneath the surface.

Common mistakes and myths

• Myth: Ceres is only an asteroid. It is the largest object in the asteroid belt and also a dwarf planet, a title it received in 2006.
• Myth: the bright spots are ice. Most of the bright material is sodium carbonate, a salt, left behind when brine reached the surface.
• Myth: Ceres has a global ocean today. Dawn found signs of a deep brine reservoir beneath Occator and suggests some briny liquid may remain. That is not the same as a global ocean.
• Myth: Dawn crashed into Ceres. The spacecraft ran out of fuel and went silent, but it remains in orbit.
• Myth: Ceres is a recent discovery. Piazzi spotted it in 1801, long before the dwarf planet category existed.

Frequently asked questions

Is Ceres a planet, an asteroid or a dwarf planet?

It is a dwarf planet, and it is also the largest object in the asteroid belt. NASA says it was once considered a planet and, for many years, an asteroid.

How big is Ceres?

NASA lists a radius of 476 km (296 miles), which makes Ceres about 952 km (592 miles) wide. NASA says it holds about 25 percent of the asteroid belt's mass.

What are the bright spots on Ceres?

They are deposits of salt, mostly sodium carbonate, left by brine that rose to the surface. The best-known spots are in Occator Crater.

Is Dawn still orbiting Ceres?

Yes, but it is no longer working. NASA says it ran out of hydrazine on October 31, 2018, and will remain in orbit for at least a couple of decades.