ES2506_final
12/05/2001
14:23
Page 6
What if Earth and the Moon Were Hit by
Twin Asteroids?
1 Predict what would happen if twin asteroids,
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each 1000 meters in diameter, were to
collide with Earth and the moon. Include a
description of the impact craters you would
expect to see on each body.
Answers will vary – look for an adequate description
ES2506
6 The acceleration of gravity (g) on Earth is 9.8
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meters/sec2, but on the moon, it is only 1.6
meters/sec2. How might this relate to the
sizes of craters produced by impacts with
identical amounts of kinetic energy on the
two bodies?
Earth’s higher g requires more energy for lifting
materials from its surface to excavate a crater. Just as an
astronaut can jump more easily on the moon, impact
energy lifts material off the moon’s surface more easily.
2 What do you think the two craters would
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look like ten million years in the future?
Answers will vary. Lunar crater will change very little;
Earth crater will be highly eroded or erased.
Crater diameters increase.
8 What happens to the diameter of impact
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Crater diameters decrease with decreased impact angle.
9 How does the kinetic energy of a 1000 m
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Earth has about 13.5 times the cross-sectional area of
diameter iron asteroid traveling at 17 km/sec
compare to the kinetic energy of an iron
asteroid with twice the mass (diameter of
1260 km) traveling at the same speed?
the moon, making it much more likely to be hit by
Kinetic energy doubles with a doubling of mass.
Earth = 127.8 million km2; moon = 9.5 million km2.
asteroids.
10 How does the kinetic energy of a 1000 m
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differ from an impact on land?
diameter iron asteroid traveling at 17 km/sec
compare to a similar one traveling at 34
km/sec?
Answers will vary. Ocean impacts could produce huge
Kinetic energy increases by a factor of four when the
tsunamis that would flood coastlines across the globe.
speed is doubled.
4 How do you think an ocean impact would
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Land impacts would result in a crater, and huge
amounts of rock materials would enter the atmosphere.
11 Use the Impact Calculator to determine the
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building) processes, volcanism, erosion, and biological
size and structure of craters on Earth and the
moon produced by asteroids with 500 m
diameters at different speeds, impact angles,
and compositions. Make a table on a
separate sheet of paper to record your
results.
activity. The moon’s surface is changed only by erosion
Students should show the estimated crater size and
from subsequent impacts.
structure for a variety of 500 km diameter asteroids.
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5 Describe the surface processes that work to
erase craters and other impact features on
Earth and the moon.
Earth’s surface is changed by tectonic (mountain-
Internet Investigations Guide
Earth Science
Copyright © McDougal Littell Inc.
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Teacher’s Guide Chapter 25
Internet Investigation
you increase the speed of the asteroids?
craters as the impact angle decreases?
3 Calculate the “target area” of Earth and the
moon. How many times larger a target is
Earth than the moon? What does this say
about Earth’s chances of being hit by an
asteroid compared to the moon’s chances?
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7 What happens to the crater diameter when
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