What Is Ceres?
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Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner solar system. About 940 km (585 miles) across, it contains 25% of the asteroid belt's total mass. Ceres was the first asteroid discovered in 1801 and was visited by NASA's Dawn spacecraft from 2015 to 2018.
Ceres is the largest object in the asteroid belt between Mars and Jupiter. Discovered in 1801, it was the first asteroid ever identified, though it's so much bigger and more spherical than other asteroids that scientists classified it as a dwarf planet in 2006. NASA's Dawn spacecraft orbited Ceres from 2015 to 2018, revealing surprising water ice and bright surface features.
Where is Ceres?
In the asteroid belt, between Mars and Jupiter. According to NASA, Ceres orbits the Sun at an average distance of 2.77 AU (about 257 million miles), taking 4.6 Earth years to complete one orbit. It's the largest object in the asteroid belt by a wide margin, comprising about 25% of the belt's total mass. Ceres is roughly 940 km (585 miles) in diameter, about the size of Texas. It's the only dwarf planet in the inner solar system; all others (Pluto, Eris, Haumea, Makemake) are in the outer solar system beyond Neptune.
Who discovered it and when?
Italian astronomer Giuseppe Piazzi on January 1, 1801. Piazzi initially thought he had found a new planet between Mars and Jupiter, where astronomers had predicted one should exist. Over the next few years, more similar objects (Pallas, Juno, Vesta) were discovered nearby. By the 1860s, astronomers had identified over 60 such bodies and classified them all as asteroids. In 2006, when the International Astronomical Union created the dwarf planet category, Ceres was included because of its size, spherical shape, and planet-like qualities.
What is Ceres made of?
Rock and ice. Ceres has a layered interior similar to terrestrial planets: a rocky core, a mantle that's largely water ice, and a crust mixed with various minerals. Ceres may be up to 25% water by mass, making it the most water-rich body in the inner solar system after Earth. NASA's Dawn spacecraft found evidence of a subsurface ocean of brine that may still be active today. Bright spots on Ceres (most famously in Occator Crater) are salt deposits left behind when subsurface brines reached the surface.
What did Dawn discover?
Many surprises. NASA's Dawn spacecraft orbited Ceres from March 2015 to October 2018, making it the first dwarf planet visited by a spacecraft. Dawn revealed bright spots in craters that turned out to be salt deposits, evidence of recent geological activity, and signs of organic molecules. The mission found that Ceres has more water than expected and may have active brine eruptions even today. Ceres is now one of several places where scientists would like to search for signs of life.
Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner solar system. About 940 km across with a rocky core and icy mantle, it was the first asteroid ever discovered (1801) and was reclassified as a dwarf planet in 2006. NASA's Dawn mission revealed a surprisingly active world with subsurface brines and bright salt deposits. Ceres is now considered a potential target for searching for signs of life.
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