Galileo image of Gaspra (29 October 1991)
Click on image for full size
NASA/JPL

Asteroids

Asteroids are small bodies that are believed to be left over from the beginning of the solar system 4.6 billion years ago. They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller.

More than 100,000 asteroids lie in a belt between Mars and Jupiter. These asteroids lie in a location in the solar system where there seems to be a jump in the spacing between the planets. Scientists think that this debris may be the remains of an early planet, which broke up early in the solar system. Several thousand of the largest asteroids in this belt have been given names.

The chances of an asteroid colliding with Earth are very small! But some do come close to Earth, like Hermes (closest approach of 777,000 km).

Last modified February 15, 2001 by Jennifer Bergman.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Impact on Jupiter - July 2009

Anthony Wesley is an amateur astronomer in Australia. On the night of July 19, 2009, Wesley noticed a dark spot on Jupiter that hadn't been there before. He had discovered the remains of a huge impact...more

Moon Found Orbiting Asteroid

A moon was discovered orbiting the asteroid, Eugenia. This is only the second time in history that a satellite has been seen circling an asteroid. A special mirror allowed scientists to find the moon...more

Japan And U.S. Join Together for Asteroid Expedition

The first asteroid collection mission has been set. Japan and the United States will join together in the MUSES-C mission. The mission is to be launched in January 2002 from Japan. The spacecraft will...more

Scientists Track Asteroids

Scientists just created an asteroid map that shows over 900 asteroids that could someday collide with Earth. Any asteroid 1 kilometer long or larger is considered a danger. Even one of these smaller space...more

Asteroid Lutetia

Lutetia is a medium-sized asteroid. It orbits the Sun in the main asteroid belt between the planets Mars and Jupiter. Its official name is "21 Lutetia" because it was the 21st asteroid discovered. Lutetia...more

Japanese Space Program Takes Off...

After a long, slow struggle, the Japanese space program is taking off! Japan's space program started with the launching of pencil-sized rockets in the 1950's. They struggled to finally build a rocket that...more

Are We From Mars?

A recent study shows there is a possibility that we came from Mars! No, that doesn't mean a spaceship flew here and dropped us off. Rather, scientists say chunks of rock were thrown off the Red Planet...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA