S e c o n d e d I t I o n 1 Reading for the Real World 1

Two Very Different Space Programs
Discussion
Discuss the following questions.
1.
Most recently, space probes have been exploring Mars and Jupiter. 
What do you think the next goal of the space program should be?
2.
Would you like to go into space? Why or why not?
Track 30

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Vocabulary Preview
 
Match each word or phrase with the correct definition.
1.
blast 
a.
the distance across a circle or sphere
2.
detect 
b. 
to change to gas by some process
3.
diameter 
c.
an explosion
4.
locate 
d.
to know by seeing or measuring
5.
strike 
e.
to hit
6.
vaporize 
f.
to find
Pre-Reading Questions
Think about the following questions.
1.
Why did the dinosaurs all die out?
2.
When was the last time a large rock from space or an asteroid hit 
Earth?
3.
Which do you think are more dangerous, big asteroids or small 
asteroids?
Asteroid Impacts 
on Earth
 
S p a c e & E x p l o r a t i o n
2
U N
I
T
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Asteroid Impacts on Earth
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A 
steroids are small objects in space. They are small compared to the 
Earth and the other planets. They are made of different kinds of rock 
or metal. They orbit the sun, mostly between the paths of 
Mars
and 
Jupiter
. Astronomers know where many asteroids are, but not all. Though they 
may seem small and far away, asteroids have hit the Earth many times, sometimes 
causing extreme destruction. It also seems clear that an asteroid will hit the 
Earth again in the future.
Most asteroids are located in what is called the “Main Belt.” This is an orbit 
between Mars and Jupiter. All of these asteroids are very far from the Earth and 
will never come close. Several hundred asteroids follow Jupiter in its orbit. 
These are called “Trojans.” Asteroids can also be found in the outer