This photograph shows Ceres moving in orbit against a starry background 8 MORE LITTLE WORLDS Another tiny world was found the year after Ceres was discovered It is a little smaller than Ceres Astronomers named it Pallas They found two more over the next five years Both are smaller than either Ceres or Pallas Astraea the fifth to be discovered is only 100 miles 160 km wide These little worlds are so small that the astronomers first described them with the term minor planets Most people however know them as asteroids a word that means like stars Modern astronomers have listed several hundred thousand asteroids One estimate has one to two million asteroids orbiting between Mars and Jupiter This region has become known as the asteroid belt At least 98 percent of all known asteroids orbit there As many as four thousand of them are larger than 0 6 mile 1 km across This sounds like an awful lot of material But if every asteroid were to be combined into one big ball it would be less than 900 miles 1 448 km wide This is less than half the size of Earth's Moon Seven Wonders of Asteroids Comets and Meteors FACTS ABOUT Ceres THE LARGEST ASTEROID Ceres is the largest known asteroid It is 568 miles 914 km across almost twice the size of the next largest asteroid It is one fourth the size of all the asteroids in the entire asteroid belt combined It is larger than most of the moons of Saturn and Jupiter Diameter 590 miles 950 km Average distance from the Sun 277 million miles 446 million km Length of year the time it takes to orbit the Sun 1,680 days
Scientists don't know much about what Ceres looks like Even in the largest telescopes it looks like a blurry ball with faint light and dark features It has a large bright spot and a large dark spot These may be giant craters on its surface It may also have a very thin atmosphere and a rocky surface covered in frost This digital illustration shows the orbits of Ceres left Mars center closest to the Sun and Jupiter bottom right as they circle the Sun A NEW KIND of Planet Scientists recently assigned Ceres to an entirely new class of solar system body They are called dwarf planets Ceres was once one of the largest asteroids but under the new classification it has become one of the smallest of the dwarf planets Pluto formerly classified as a planet Ceres and Eris an icy body that orbits far beyond Pluto were the first three objects to be put into this new category
The Dawn space probe is seen near the asteroid Vesta left and the dwarf planet Ceres right in this illustration Dawn was launched in 2007 On September 27 2007 the National Aeronautics and Space Administration NASA launched the Dawn spacecraft Its mission is to explore the asteroid belt It is scheduled to visit the asteroid Vesta in 2011 and Ceres in February 2015 As the spacecraft swings close to Ceres it will take photos and scan the surface of the asteroid This will help scientists learn what Ceres is made of and how it was formed Seven Wonders of Asteroids Comets and Meteors THE ASTEROID ZOO Asteroids come in all sizes and shapes They range from rocks only a few hundred feet across to flying mountains 500 miles 800 km wide The very biggest are round But smaller objects have weaker gravity A large body such as Earth tends to be round Every point on the surface of Earth is just about the same distance from the center This is because its gravity is strong enough to flatten out any large lumps But with much less gravity to pull at an asteroid's surface it can be any shape at all The first asteroid to be explored by a spacecraft was 433 Eros The Near Earth Asteroid Rendezvous NEAR Shoemaker spacecraft launched in 1996 10 The asteroid belt is a great grinding mill producing smaller and smaller pieces down to motes of dust Carl Sagan American astronomer Cosmos 1980
Ceres 11 photographed its surface The photos showed that 433 Eros is shaped like a giant cashew nut measuring 22 x 8 x 8 miles 35 x 13 x 13 km A deep saddlelike dent in the middle separates two bulging ends While the rest of Eros is heavily cratered the saddle is remarkably smooth The saddle might be a huge dent caused by a collision with another asteroid Gravity The amount of gravity a body has depends on how much mass it has The bigger and heavier something is the more gravity it produces Earth has about 6 trillion tons 5 trillion metric tons of mass Mass is the amount of stuff that an object contains Earth's gravity makes you weigh what you do and pulls you back down when you jump A small asteroid like 624 Hektor has much less mass than Earth As a result Hektor's gravity is 150 times less than Earth's You would be able to jump from one end of Hektor to the other easily In fact you would have to be very careful not to launch yourself off into space Top Lumpy 433 Eros was the first asteroid to be photographed up close by a spacecraft Its saddle shaped dent can be seen at the lower edge Bottom The NEAR Shoemaker spacecraft took this photo of 433 Eros's horizon
