Asteroid Background
1st source: What is an Asteroid? http://www.edunet.ie/stlaur/whatast.html. 01 Dec 2004.
There are 3 asteroids close to earth: Ceres, Vesta, and Pallas asteroids
Asteroid Belt: The asteroid belt lies between the orbits of Mars and Jupiter.
Trojan asteroids- located 60 degrees in front of and behind the orbit of Jupiter
Amor asteroids- cut across the orbit of Mars
Apollo asteroids- cut across the orbit of the Earth and are probably to blame for the asteroid craters on earth. They may possibly be a source of metals and other minerals for us to mine in space in the future.
There is a graph of the asteroids in our solar system at: http://www.edunet.ie/stlaur/belt.html
Finding Asteroids:
In the early days, asteroids were very hard to find. First they had to make a map of a region of the sky. Then, after some time had passed, they would make another map of the same area. If any of the objects had moved they were asteroids.
In 1891 celestial photography was invented allowing astronomers to ensure faster asteroid searching. The exposure of the photographic plate in the telescope could last several hours being pointed at exactly the same spot. When the plate was developed, asteroids could be seen clearly marked by a streak on the photograph due to its movement.
2nd Source: Calvin J. Hamilton. “Asteroid Introduction.” http://www.solarviews.com/eng/asteroid.htm. 01 Dec 2004.
Asteroids are miniature or “minor planets” in our Solar System that consist of rocky and metallic matter (Hamilton, “Asteroid Introduction”) They orbit the Sun, just like Earth, but are too small to be considered planets. Some asteroids, known as binary asteroids, can have their own satellite circling it (“What is an Asteroid?”). Asteroids are in a way like space junk, material left over from the formation of the solar system. Some scientists believe that they are the remains of a planet that was destroyed in a massive collision long ago; however, it is more probable that asteroids are simply material that never coalesced into a planet.
Interesting Fact: If the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across -- less than half the diameter of our Moon.Asteroids that are on a collision course with Earth are called meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite.
On June 27, 1997 the NEAR spacecraft made a high-speed close encounter with asteroid 253 Mathilde. This encounter gave scientists the first close-up look of a carbon rich C-type asteroid. This visit was unique because NEAR was not designed for flyby encounters. NEAR is an orbiter destined for asteroid Eros in January of 1999.
3nd Source:
Asteroid Fact Sheet. http://nssdc.gsfc.nasa.gov/planetary/factsheet/asteroidfact.html. 01 Dec 2004
Communications with the NEAR spacecraft on the surface of Eros ended at 7 p.m. on February 28th, 2001.
1 Ceres - The largest and first discovered asteroid, by G. Piazzi on January 1, 1801. Ceres comprises over one-third the 2.3 x 1021 kg estimated total mass of all the asteroids.2 Pallas - The 2nd largest asteroid and second asteroid discovered, by H. Olbers in 1802.
3 Juno - The 3rd asteroid discovered, by K. Harding in 1804.
4 Vesta - The 3rd largest asteroid, Vesta appears to have a basaltic crust overlying an olivine mantle, indicating differentiation has occurred. Imaged by the Hubble Space Telescope in 1995.