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Asteroids
Sixty-Five million years ago, 70 percent of life on Earth
died. The most reasonable and possible reason this happened was an asteroid. An
asteroid hit the Earth very hard, and in doing this, dirt and dust from the
impact stayed in the air and it blocked out sunlight, that’s why the dinosaurs
died. An asteroid is a rock from outer space. Asteroids have orbited the Sun
along with the planets since the solar system formed about 4.6 billion years
ago, but it’s only been 200 years since we first discovered them. Meteorites are
small pieces of asteroids broken off on impact with other asteroids. Most
meteorites are rusty brown on the outside, have rounded edges from melting as
they go through Earth’s atmosphere, and contain iron. There are 3 different
types of meteorites: stony, metallic, and stony metallic.92 percents of all
asteroids are stone, 6 percent are made of iron and nickel, and the rest are a
combination. Some meteorites also contain gold, copper, platinum, and carbon.
Scientists get a good idea of what asteroids are made of by studying
them through telescopes. They can tell what an asteroid is made of by the color
and brightness of the asteroid. A lot of asteroids that we have discovered are
very dark and made of stone, but there are shiny ones that are made of nickel
and iron.
Most big asteroids are ball shaped. Smaller asteroids, which
are usually broken off of a larger asteroid, come in a lot of different shapes.
All asteroids have craters that form when they bump or crash into other
asteroids. The older the asteroid, the more times it has been hit and the more
craters it has.
Asteroids can be found orbiting the Sun in a belt
between Mars and Jupiter; this is called the Asteroid belt or Main belt. The
asteroid belt has been said to probably contain millions of asteroids that are
all different. There are more than 20,000 numbered asteroids. Some times
asteroids get knocked off the asteroid belt. As asteroids revolve around the Sun
in elliptical orbits, Jupiter’s gravity and getting to close to Mars or another
asteroid can change an asteroids path, this could send an asteroid out of the
asteroid belt and into space across the orbits of other planets. An example of
asteroid orbits changing is Mar’s moons Phobos and Deimos. These were asteroids
that went to close to Mars and got caught in its orbit.
Right now, a
22-mile wide asteroid called Eros is in an orbit that is close to Earth’s orbit.
Eros is twice the size of the asteroid that killed the dinosaurs. Eventually,
Earth will be in Eros’s path. This asteroid could kill all life on Earth if it
hits us. All scientists can do right now is study it to learn if there is anyway
to avoid it, or get rid of it. Not all asteroids are as dangerous as this one.
Most of the time they float around harmlessly in space. Asteroids don’t hit each
other a lot. Asteroid belts aren’t like in the movies where the asteroids are
very close. They can sometimes be millions of miles away.
Even though
scientists call asteroids “minor plants”, they are very different that planets.
Asteroids are much smaller than planets and are shaped differently. Most
asteroids do not have enough gravity to pull them into regular spheres, so
instead of being shaped like a grapefruit, they are shaped like a potato.
Asteroids come in a variety of sizes and shapes just like potatoes. The largest
asteroid we know of right now is Ceres. Ceres could almost cover an area the
size of Alaska. Ceres is 578 miles across.
Astronomers have found about
200 asteroids that are wider than 62 miles. Some asteroids contain water, carbon
and other things that are necessary to support life. There is a theory that
asteroids that were carrying water carbon and other things to support life,
brought these to Earth billions of years ago, and started life on Earth.
One of the things I learned about asteroids on this project is that some
have moons. On 1993 in August, the space probe Galileo flew past an asteroid
named Ida. It took a few close pictures and scientists looked at the pictures
and discovered that there was a moon orbiting around Ida. The scientists named
this moon Dactyl. Now scientists think many asteroids have moons. I believe this
because it’s the way gravity works. Even though asteroids do seem harmless, each
person has a 1 in 20,000 chance of dying from a natural disaster like asteroids,
hurricanes, tornados, earthquakes, and floods.
Bibliography
“Asteroids”- By Samantha Bonar
“The Three Big Bangs”- By Philip Dauber
“Comets, Asteroids and Meteorites”- By Cynthia Nicolson
http://solarsystem.nasa.gov/features/planets/asteroids/asteroids.html