Earth Science Lesson 1
The Solar System

Pre-Test
Q&A	The Small Pieces: Asteroids, Comets, and Pluto

Instruction 1-6

The Solar Nebula/Earth's Formation from the Nebula | Cloud of Dust Theory | Formation and Origin of the Moon | Early Earth | The Sun | Effects of Asteroid Impacts in Shaping the Surface of Planets | Evidence for the Existence of Planets Orbiting Other Stars | Summary

Effects of Asteroid Impacts in Shaping the Surface of Planets
http://www.lpi.usra.edu/publications/slidesets/craters/

Have you ever seen a movie where the Earth is about to be hit by an object from outer space? Well, that isn’t just science fiction. It’s science fact. Because there are objects out there just waiting to crash into us. But most of them don’t come from outer space. They come from right within inside our own Solar System. Those objects are called asteroids.

Asteroids are rocky, metallic bodies that revolve around The Sun. They have no atmosphere like the Earth. Some are made up of matter left over from the formation of the Solar System. Others are made of material spewed out from the hot interiors of planets. They can be as big as 600 miles wide -- but they are not big enough to be called planets. Others are as small as marbles. But even the smallest asteroid can cause serious damage.

Tens of thousands of asteroids rotate in an elliptical ring between the orbits of Mars and Jupiter. This ring is called “the main belt.” The asteroids that threaten the Earth have somehow managed to escape from this belt.

How? We’re not sure. But somehow they move to an unstable part of the belt called a resonance. Once there, the gravity from nearby planets (Mars, Jupiter or Saturn) elongates their orbits. This swings them into an orbit that could collide with Earth. And when that happens – disaster!

For example, it is estimated that an asteroid only 1 km (0.6 miles) in diameter could kill a quarter of the people on earth. Less than100 years ago, an asteroid only 330 feet wide exploded over Siberia. It leveled more than half a million acres (2,000 square km) of forest. In 1986, the Earth came within 6 hours of being struck by a dangerous asteroid. And we didn’t even know about it till afterwards.

When a big asteroid does hit, it changes things forever. An asteroid six miles wide hit the Earth 65 million years ago. This asteroid struck near what is now Mexico’s Yucatan Peninsula and wiped out almost all living things – including the dinosaurs! Other planets are also constantly being struck by asteroids. This has been going on for billions of years and has had a major impact on the surface of all the planets, which are covered with huge depressions called craters.

One of the most visible examples of an asteroid hit is Meteor Crater in Arizona. Scientists estimate that this hit happened about 50,000 years ago. To see a picture of Meteor Crater, click on http://www.meteorcrater.com.

Talking about Meteor Crater brings up a small matter of semantics (words). Why is it called Meteor Crater if it was hit by an asteroid? Shouldn’t it be called Asteroid Crater?

People do confuse the words asteroid and meteor. But asteroids and meteors are different things. As we’ve learned, asteroids are bodies that orbit The Sun. Meteors are bits of the Solar System that can come from anywhere – asteroids, comets, the Moon or even Mars. And what are meteorites? Little meteors.

But back to asteroids. What are our changes of being hit by one? Scientists say that our short-term chance of being hit by an asteroid is small. Over time, however, it’s inevitable.

The wake-up call about asteroids really came with the spectacular 1994 crash of the asteroid Shoemaker-Levy into the planet Jupiter. This event was watched in real time by astronomers everywhere – and the Hubbell Space Telescope’s pictures of it were all over TV. For more about the history of asteroid impacts, click: http://whyfiles.org/106asteroid/2.html

Scientists estimate that there are over 1100 asteroids which could strike the Earth. Only half of these asteroids have been discovered. That’s why the search for near-earth asteroids (NEAs) is heating up.

Thousands of people all over the world are looking for them. One reason may be that an asteroid is named for the person who discovers it (and we all like to see our names on things). A more important reason, of course, is to try and prevent a disastrous collision.

Currently the United States is in the middle of a project to orbit Eros, the second largest near-earth asteroid we know of. This will help us understand the makeup of asteroids and how they behave. This information is vital if we ever have to explore an asteroid. Or if we have to try to explode one or deflect it from striking Earth. But everything about asteroids isn’t frightening or dangerous.

Scientists believe that many of the chemical components of life, including water, were originally brought to earth by asteroids. Some asteroids are thought to have enough water on them to sustain the life of space pioneers. Or that this water could be broken down into hydrogen and oxygen for rocket fuel.

And many people think that asteroids can eventually be mined for metals like iron and nickel. In fact, NASA has even developed a robot that could help us do this. It hops like frog so it can operate in places with little gravity. What is it called? You guessed it. Frogbot.

Asteroids could also be moved into Earth’s orbit or brought down to the Moon for mining operations. Or even broken into pieces and landed in remote locations on earth. So asteroids aren’t just scary, they can be put to work for us. Although scary does make for a more exciting movie.

To learn more about asteroids, go to:

http://news.nationalgeographic.com/news/2000/12/1220_asteroid.html

Experiments for Home and Classroom

The Earth, the Moon and other planets are constantly being struck by asteroids from the Asteroid Belt as well as by meteors from elsewhere in the Solar System. In this activity, students replicate the creation of impact craters on the Moon. Click: http://www.spacegrant.hawaii.edu/class_acts/Craters.html 

In this second "impact" experiment, students continue to investigate the formation of impact craters and see examples of large impact sites like Meteor Crater in Arizona. Click: http://cse.ssl.berkeley.edu/AtHomeAstronomy/activity_05.html 

Asteroids are bodies that orbit the Sun. Meteors are bits of the solar system that can come from anywhere -- from asteroids, comets, the Moon or even from Mars. Meteorites are little meteors. Collecting meteorites can be a fascinating (and sometimes profitable) activity. Here's how:  http://space.about.com/od/backyardscience/qt/collmeteorites.htm

Students are invited to destroy a virtual asteroid before it can destroy them. Play the Asteroid Attack game online at:
http://www.bbc.co.uk/science/space/playspace/games/asteroids/asteroids.shtml  

Now let's do Practice Exercise 1-6 (top)

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