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Ancient Space Rubble
Asteroids are rocky fragments left over from the formation our the solar system about 4.6 billion years ago. Most of these chunks of space rubble, sometimes called minor planets, can be found orbiting the Sun in a belt between the orbits of Mars and Jupiter. The Asteroid Belt or Main Belt probably contains millions of asteroids.

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Queen of the Asteroid Belt
With a diameter of 933 km (580 miles), Ceres is the undisputed ruler of the asteroid belt. The space rock accounts for a quarter of all the mass of all the known asteroids in or near the main asteroid belt.
Queen of the Asteroid Belt
Small Change
If you could lump together the more than one half million asteroids known to reside in the asteroid belt their total mass wouldn't even equal the Earth's moon.
Small Change
Asteroid Assault
Asteroids have hit every planet in our solar system. Most space rocks that hit Earth disintegrate or slow down enough not to cause serious damage. Evidence of what happens when they don't can be seen at Barringer Crater in Arizona -- a giant hole almost 1.6 km (1 mile) across and 175 m (570 feet) deep.
Asteroid Assault
Close Call
An asteroid named 1950 DA is considered one of the greatest known threats to crash into Earth. Fortunately, the odds of an impact are fairly slim. The asteroid won't arrive until 16 March 2880, so we have a few hundred years to watch it and make certain it will miss Earth.
Close Call
Tiny Guardian
Asteroids are often called minor planets. Some even have moons. Back in 1994, NASA's Galileo spacecraft found a tiny moon -- about 1.5 km (1 mile) across -- orbiting Asteroid Ida. The first known moon of an asteroid was named Dactyl, after the protectors of the young Greek god Zeus.
Tiny Guardian
Touchdown
After NASA's NEAR spacecraft had completed its intensive study of asteroid Eros, mission controllers decided to try to land the spacecraft. Despite the fact it wasn't designed for landing, NEAR successfully touched down on Eros in 2001 -- and went into the record books as the first spacecraft to land on an asteroid.
Touchdown
Dino-Killer
It is possible that a gigantic asteroid impacted the Earth and led the extinction of the dinosaurs.
Dino-Killer
Two Times One Equals ... Binary
Ever hear of a binary star system, or a binary planet system? Yes? Well, add binary asteroids to your list too. Binary (double) asteroids are two rocky bodies of roughly equal size that orbit each other. Guess what? There are triple asteroid systems as well.
Two Times One Equals ... Binary
Moon Masters
The planet Jupiter has the most moons with a total of 67. However -- in terms of a moon count -- all the asteroids of the asteroid belt beat out Jupiter: More than 150 of the asteroids are known to have a small companion moon and some even have two moons; that is over 150 moons for the asteroids.
Moon Masters
Space in Space
The asteroid belt is not a dense field of rocks and debris that we often see in the movies. Asteroids are very far apart from one another. The average distance between asteroids in the main belt is about two million km (1.2 million miles). The United States spans about 4,828 km (three thousand miles) from coast to coast. This means that the average distance between two asteroids is about the distance of the United States times 400.
Space in Space
No Small Matter
Asteroids range in size from the biggest (Ceres) being about 952 km (592 miles) in diameter, to bodies that are less than one kilometer (0.6 mile) across. However one kilometer is still pretty big: One kilometer is equal to 1,094 yards, which is about the length of 11 football fields (minus the end zones) spread out end to end.
No Small Matter
Impact
About once a year an automobile-sized asteroid enters Earth's atmosphere, creates an impressive fireball and disintegrates before ever reaching the surface.
Impact
A First
Before 2011, an asteroid had never been orbited by a spacecraft. Dawn is the first spacecraft to orbit an asteroid.
A First
Queen of the Asteroid Belt
With a diameter of 933 km (580 miles), Ceres is the undisputed ruler of the asteroid belt. The space rock accounts for a quarter of all the mass of all the known asteroids in or near the main asteroid belt.
Queen of the Asteroid Belt
Small Change
If you could lump together the more than one half million asteroids known to reside in the asteroid belt their total mass wouldn't even equal the Earth's moon.
Small Change
Asteroid Assault
Asteroids have hit every planet in our solar system. Most space rocks that hit Earth disintegrate or slow down enough not to cause serious damage. Evidence of what happens when they don't can be seen at Barringer Crater in Arizona -- a giant hole almost 1.6 km (1 mile) across and 175 m (570 feet) deep.
Asteroid Assault
Close Call
An asteroid named 1950 DA is considered one of the greatest known threats to crash into Earth. Fortunately, the odds of an impact are fairly slim. The asteroid won't arrive until 16 March 2880, so we have a few hundred years to watch it and make certain it will miss Earth.
Close Call
Tiny Guardian
Asteroids are often called minor planets. Some even have moons. Back in 1994, NASA's Galileo spacecraft found a tiny moon -- about 1.5 km (1 mile) across -- orbiting Asteroid Ida. The first known moon of an asteroid was named Dactyl, after the protectors of the young Greek god Zeus.
Tiny Guardian
Touchdown
After NASA's NEAR spacecraft had completed its intensive study of asteroid Eros, mission controllers decided to try to land the spacecraft. Despite the fact it wasn't designed for landing, NEAR successfully touched down on Eros in 2001 -- and went into the record books as the first spacecraft to land on an asteroid.
Touchdown
Dino-Killer
It is possible that a gigantic asteroid impacted the Earth and led the extinction of the dinosaurs.
Dino-Killer
Two Times One Equals ... Binary
Ever hear of a binary star system, or a binary planet system? Yes? Well, add binary asteroids to your list too. Binary (double) asteroids are two rocky bodies of roughly equal size that orbit each other. Guess what? There are triple asteroid systems as well.
Two Times One Equals ... Binary
Moon Masters
The planet Jupiter has the most moons with a total of 67. However -- in terms of a moon count -- all the asteroids of the asteroid belt beat out Jupiter: More than 150 of the asteroids are known to have a small companion moon and some even have two moons; that is over 150 moons for the asteroids.
Moon Masters
Space in Space
The asteroid belt is not a dense field of rocks and debris that we often see in the movies. Asteroids are very far apart from one another. The average distance between asteroids in the main belt is about two million km (1.2 million miles). The United States spans about 4,828 km (three thousand miles) from coast to coast. This means that the average distance between two asteroids is about the distance of the United States times 400.
Space in Space
No Small Matter
Asteroids range in size from the biggest (Ceres) being about 952 km (592 miles) in diameter, to bodies that are less than one kilometer (0.6 mile) across. However one kilometer is still pretty big: One kilometer is equal to 1,094 yards, which is about the length of 11 football fields (minus the end zones) spread out end to end.
No Small Matter
Impact
About once a year an automobile-sized asteroid enters Earth's atmosphere, creates an impressive fireball and disintegrates before ever reaching the surface.
Impact
A First
Before 2011, an asteroid had never been orbited by a spacecraft. Dawn is the first spacecraft to orbit an asteroid.
A First