Landsat 7 Educational Activity for Grades 5-8

Finding Impact Craters with Landsat

♦ **Activity Summary**

Students consider the sudden release of a tremendous amount of kinetic
energy when an extraterrestrial object strikes the Earth. They write
about the effects that such a collision might have on the land,
atmosphere, water, and living things.

Students then read descriptions of the actual effects of impact events
and the evidence these leave behind. In small groups, they study
satellite images that show possible evidence of impact events. They
select one or two of these images to interpret for the class. In their
interpretations, they explain how the image does or does not show
evidence of an impact event.

To demonstrate their understanding of the role of impact events in
shaping the Earth, students write a series of guidance questions for a
field expedition to determine whether or not a given landform is an
impact crater.

**♦ Grade Level: 5-8**

♦ Time

Two class periods (about 90 minutes) with pre-activity assignment and
post-activity learning assessment as either homework or class work

**♦** **Goals for Student Learning**

**Students will:**

→ **Describe the effects of extraterrestrial objects upon the Earth\'s
topography, atmosphere, and living organisms**

→ **Describe the role of satellite technology in helping scientists to
identify evidence of impact events**

→ **Describe why and how science is an ongoing process of discovery**

**♦ National Standards**

[Benchmarks for Science Literacy]{.underline}

4C 6-8 #2. Some changes in the Earth\'s surface are abrupt (such as
earthquakes and volcanic eruptions) while other changes happen very
slowly (such as uplift and wearing down of mountains). The earth\'s
surface is shaped in part by the motion of water and wind over very long
times...

The activity can be linked to teaching this benchmark:

4E 6-8 #2. Most of what goes on in the universe...involves some form of
energy being transformed into another. Energy in the form of heat is
almost always one of the products of an energy transformation.

[National Science Education Standards]{.underline}

Earth and Space Science Standard for Grades 5-8: The earth processes we
see today...are similar to those that occurred in the past. Earth
history is also influenced by occasional catastrophes, such as the
impact of an asteroid or comet.

The activity can be linked to teaching this standard:

Transfer of Energy Standard for Grades 5-8: Energy is a property of many
substances and is associated with heat, light, electricity, mechanical
motion, sound, nuclei, and the nature of a chemical. Energy is
transferred in many ways.

.

**♦ Materials and Resources Provided**

>  Student worksheets
>
> Student Worksheet for Step 1: *When an Extraterrestrial Object Hits
> the Earth*
>
> Student Worksheet for Step 2: *Known Effects of Impact Events*
>
> Student Worksheet for Step 4: *Describing Satellite Images of Possible
> Impact Craters*
>
> Student Worksheet for Step 6*: **Questions You Would Ask on a Field
> Expedition to a Possible Impact Crater***
>
>  Satellite images of landforms with pseudonyms for student use
> (Students may recognize some names and know already whether or not
> they\'re impact craters.)
>
> Aorounga (Aor)
>
> Elgygytgyn (Elg)
>
> Haughton (Hgh)
>
> Manicougan (Man)
>
> Mount St. Helens (Msh)
>
> Richat (Rch)
>
> Schooner (Sch)

#########  Diagrams of simple and complex impact structures

> http://cass.jsc.nasa.gov/expmoon/science/craterstructure.gif
>
>  Rubric for student learning assessment

**♦ Materials and Resources Needed from Teachers**

> Unless each student will have access to this activity online, teachers
> will need transparencies or paper to make student copies of the
> satellite images. (Please see Step 4.)

**♦ About More Satellite Images**

>  A small selection of other images of Aorounga, Elgygytgyn, Haughton,
> and Manicougan can be found at the Earth Impact Database, Crater Image
> Archive: http://www.unb.ca/passc/ImpactDatabase/images.html

♦ **Student Prerequisites**

>  Students should understand what a satellite is and should have a
> basic level of comfort with looking at the Earth from space.
>
>  Students should understand that satellite images are not
> photographs. Researchers use very different kinds of technology to
> produce photographs and satellite images.
>
>  Student should also understand that most satellite images use false
> colors to display information. The satellite images provided with this
> activity use false colors.

♦ **Teacher Preparation**

**→** [Read and become familiar]{.underline} with the Background section
and any additional resources you think might help you. See \"Relevant
Resources\" at the end of the section, *Background: Impact events are
Key to Earth\'s History.*

**→** [Read all the way through the lesson plan]{.underline} to tailor
the ideas to your class and to be comfortable with the sequence and
information.

**→** [Consider running a classroom lab]{.underline} that gives
students\' experience at making craters of their own. Guidelines for
such an activity can be found at:

> Deep Impact: Making Impact Craters!
>
> http://cass.jsc.nasa.gov/education/EPO/explore/craters.pdf
>
> Although impacts of extraterrestrial objects onto the Earth\'s surface
> occur at hypervelocity (high speed) and involve much more kinetic
> energy [than]{.underline} any impacts in a classroom lab [might
> do,]{.underline} such a lab can be worthwhile. [In this classroom
> lab]{.underline}, students make craters themselves and
> [can]{.underline} notice how impacts of different-sized objects at
> different angles can produce differently shaped craters.

**→** [Make student copies]{.underline} of the satellite images on
transparencies or paper.

> Indicate the abbreviated name of the landform on each student copy of
> the image. (See \"Materials and Resources Provided.)
>
> If you use the full name, some students may recognize the landform as
> an impact crater or other landform such as a volcano known to them
> (Mount St. Helens).

**→** [Make student copies]{.underline} of the worksheets and readings:

> Student Worksheet for Step 1: *When an Extraterrestrial Object Hits
> the Earth*
>
> Student Worksheet for Step 2: *Known Effects of Impact Events*
>
> Student Worksheet for Step 4: *Describing Satellite Images of Possible
> Impact Craters*
>
> Student Worksheet for Step 6*: Questions You Would Ask on a Field
> Expedition to a Possible Impact Crater*
>
> [Please Note]{.underline}: It is recommended that teachers
> [not]{.underline} distribute student readings before it is indicated
> to do so in the activity steps below. If students apply their own
> existing knowledge to a problem before doing the reading, the teacher
> will (1) have a better grasp of what the students know before they
> complete the activity; (2) give the students a chance to struggle with
> a problem and bring all their own resources to bear on it.

♦ **Student Learning Assessment**

> Pre-activity assessment: Use student responses on Student Worksheet
> for Step 1: *When an Extraterrestrial Object Hits the Earth* to learn
> what ideas students already have about how impact events have shaped
> the Earth.
>
> Post-activity assessment: Use *Student Learning Assessment for Step 6:
> Questions You Would Ask on a Field Expedition to a Possible Impact
> Crater*
>
> A rubric for scoring the worksheets appears at the end of this
> activity
>
> Comparing pre-activity and post-activity student responses to the
> worksheets for Steps 2 and 6 should provide a picture of what students
> have learned.

♦ **Background: Impact events are Key to Earth\'s History.**

Many people know that craters cover the surface of the moon. In fact,
impact craters appear on all rocky (terrestrial) planets and many of
their moons. The Earth has been shaped by these dramatic impact events
no less than other planetary bodies have been, and one can see evidence
on the Earth in terms of its geology, biology, and chemistry. The
knowledge we can gain from studying impact craters is fundamental and
interdisciplinary.

Science is an exploratory, dynamic process, and new ideas frequently
come to light. Until about 40 years ago, impacts by extraterrestrial
objects were not considered very significant by most geologists. Impact
events are now recognized as more abundant, larger, older, more
geologically complex, more economically important, and even more
biologically significant than scientists had believed. Impact events
have formed major ore deposits, generated large crustal disturbances,
and produced huge volumes of igneous rock. We know that at least one
major biological extinction event was probably triggered by the impact
of an extraterrestrial object, and the coastline of Chesapeake Bay was
partially shaped by an impact event. Impact events may have played a key
role in the formation of the ocean basins and of the oceans themselves.
Large impacts can drastically alter the chemical composition of the
atmosphere.

Researchers have identified approximately 140 individual impact craters
on Earth. These craters probably represent only about 25 percent of
those to be found. Assuming an equal rate of impact around the globe,
many more craters remain to be discovered, particularly in remote land
regions of our planet and in the oceans.

NASA scientists currently study satellite images for evidence of impact
events. Finding the evidence requires careful interpretation of
satellite images. Wind and water have eroded away most of the evidence;
various other geologic processes have concealed it; oceans and
vegetation now cover much of the rest. Satellite observation technology
enables us to see landforms that we can\'t see with our eyes alone. When
impact craters are found in satellite images, interdisciplinary teams of
scientists can go to the sites on the ground to learn more about them
and how they have changed their surroundings.

These are some questions scientists are currently asking about impact
events:

> \> How often do impacts occur? Does the rate of impacts vary over
> time? If so, does it vary regularly or randomly?
>
> \> Are asteroids or comets the more frequent impacting bodies?
>
> \> Have impact events caused more than one major biological extinction
> event?
>
> \> When will the next impact event take place? How big will it be, and
> how will it affect life?

♦ **[Resources for Learning More]{.underline}**

## [About Impact Events -- General]{.underline}

*Craters! A Multi-Science Approach to Cratering and Impacts.* William K.
Hartmann with Joe Cain. 1995. (National Science Teachers Association)
http://www.nsta.org/recommends/product.asp?id=12174

## *Educator\'s Guide to Impact Craters*

## http://www.solarviews.com/eng/edu/craters.htm

### *Meteors, Meteorites, and Impacts*

http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorites.html

## *\"What is a Bolide?\"* U.S. Geological Survey

http://woodshole.er.usgs.gov/epubs/bolide/introduction.html#simple_vs_complex_impact_craters

## [For Advanced Student and Teacher Background]{.underline}

***Earth Impact Database.*** Natural Resources Canada

http://www.unb.ca/passc/ImpactDatabase/essay.html

### *Exploring Space, Exploring Earth: New Understanding of the Earth from Space Research*

### Paul Lowman. 2002. (Cambridge University Press)

## 

## *Mars crater identification and aging with NASA Ames Research Center*

## http://clickworkers.arc.nasa.gov/top

## *Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures.* Bevan M. French

## http://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html

Available in print for just the cost of shipping, from:

> Order Department, Lunar and Planetary Institute
>
> 3600 Bay Area Boulevard
>
> Houston, TX 7058-1113, USA
>
> Phone: 281-486-2172; Fax: 281-486-2186
>
> E-mail: order@lpi.jsc.nasa.gov

######## About Risk of Impact

### *Asteroid and Comet Impact Hazards*

http://impact.arc.nasa.gov/reports/spaceguard/index.html

***Spacewatch.*** University of Arizona\'s Lunar and Planetary
Laboratory

http://spacewatch.lpl.arizona.edu/

[About the Chesapeake Bay Impact Crater]{.underline}

***A Cosmic Tale: Mystery in Seven Parts.*** Landmark Communications,
Inc.

http://www.pilotonline.com/special/meteor/

####### **Investigating the Chesapeake Bay Impact Crater.** U.S. Geological Survey (USGS)

http://geology.er.usgs.gov/eespteam/crater/

NASA Landsat 7 Educational Activity

[Finding Impact Craters with Landsat]{.underline}

 Lesson Plan 

Step 1 . Use students\' interest in the highly dramatic, explosive to
introduce the activity.

> Show students an aerial photograph of [Barringer Meteor Crater]{.mark}
> (also known as \"Meteor Crater\", and located in Arizona). Tell them
> this landform is about 1300 meters (0.8 mile) in diameter and 174
> meters (570 ft) deep. Ask them, what do you think could have made a
> hole this big in the land? Discuss as a class.
>
> Show an artist\'s rendering of an impact event. Two are provided.
>
> 1\. \"One Minute After the End of the Cretaceous\" by William K.
> Hartmann [\[\"Chicxulub #3 of 5 -- 100 dpi.jpg\"\]]{.mark}
>
> *Please be aware* that anyone reproducing this painting for uses
> [other than]{.underline} this classroom activity, \"Finding Impact
> Craters with Landsat\" must contact William K. Hartmann for his
> permission, at: \<hartmann@psi.edu\> or by using information at this
> URL:
> http://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html
>
> 2\. [Impact Painting by Don Davis]{.mark} (Use hotlink or go to:
>
> \< http://www.donaldedavis.com/PARTS/K-TNASA.jpg \>
>
> Tell students that many objects much smaller than a planet orbit the
> Sun, and sometimes the Earth\'s path crosses theirs. When that
> happens, there is an impact event of enormous force, with profound
> effects on rocks and soil, atmosphere, water, and living things.
>
> Ask students to imagine hitting a dust particle or a fleck of paint in
> the air with their finger. They will understand that such a collision
> would not leave any lasting mark. Tell them that NASA engineers
> working on the Space Shuttle have found that even tiny flakes of paint
> floating in space (from earlier missions) can make craters one
> centimeter in diameter in Space Shuttle windows when they hit them,
> because of the speed of impact. Emphasize that there is a lot of
> energy in an object traveling fast. It has been calculated that the
> energy required to produce the Barringer crater was equivalent to the
> explosion of 15 million tonnes of TNT.
>
> Have a discussion about what students may already know about impact
> events. Ask students if any of them have visited Barringer Meteor
> Crater. Students who have done so can describe their experience.
>
> *[Do the following either in the classroom or as homework the night
> before you wish to conduct the bulk of the lesson]{.underline}:*
>
> Distribute the Student Worksheet for Step 1, \"When an
> Extraterrestrial Object Hits the Earth\".
>
> On the worksheet, students read a short description of what happens
> during an impact event. Based on that reading and on their existing
> knowledge, they describe the effects such an event might have on the
> land, air, and living things, and evidence of these effects that might
> remain for thousands or millions of years.

*In the classroom:*

Step 2. Distribute Student Reading for Step 2: *Known Effects of Impact
Events*, and have students read quietly alone or aloud together.

Step 3. Show either of the following, both of which are provided with
this activity:

> \(a\) the movie, \"Iturralde Movie\"
>
> [or]{.underline}
>
> \(b\) the series of three still images from the movie, \"Iturralde
> Stills\", which is provided with this activity.
>
> Explain to students that the movie is made of Landsat images of a
> location in Bolivia, made of the same data but displayed in different
> ways by NASA scientists as the movie progresses. The movie and the
> series of still images taken from it show very clearly how satellite
> technology helps us see landforms hidden in the Earth\'s surface that
> we cannot see with our eyes alone.

Step 4. Organize students in small groups (of three to five students).
Distribute the following:

> \(1\) One set of seven satellite images to each group
>
> \(2\) One copy for each student of the Student Worksheet Sheet for
> Step 4*:* *Describing Satellite Images of Possible Impact Craters*
>
> Given what students know about the evidence left by impacts, ask
> student groups to determine whether or not the landforms in all seven
> of the images [appear to be]{.underline} impact craters.
>
> Guidance questions are provided on the Student Worksheet.
>
> [Monitor the student groups]{.underline} as they discuss their
> analyses of the satellite images.
>
> 1\. Make sure students understand that they should come to agreement
> as a group about their satellite images based on their analysis of the
> evidence in the images.
>
> 2\. The Student Worksheet provides instructions about sharing their
> thoughts about the evidence before coming to agreement as a group. As
> groups discuss their analyses of the images, make sure they are
> discussing the evidence constructively with each other.
>
> 3\. If students do not follow these instructions in the worksheet,
> direct them to choose one or two of the satellite images they find
> most interesting to interpret for the class, and to designate a
> spokesperson for the group.

Step 5. Have each spokesperson interpret the group\'s images. Make sure
that all of the images in the set provided are covered in the class
discussion.

> Whether or not students believe each image shows an impact crater,
> their spokesperson must explain their group\'s thinking clearly and
> convincingly.
>
> For positive identifications of the landforms as needed, use the
> *Teacher Reference for Step 5: The Landforms Identified*.

*Either in the classroom or as homework:*

Step 6. Distribute Student Worksheet for Step 6: *Questions You Would
Ask on a Field Expedition to a Possible Impact Crater*

> Ask students to write a set of questions for researchers going on a
> field expedition to an unidentified landform. The questions should
> serve well as guidance to determine whether or not the landform could
> be positively identified as an impact crater.

Landsat 7 Educational Activity Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Finding Impact Craters with Landsat

Student Name:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Class Period: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Student Worksheet for Step 1:**

***When an Extraterrestrial Object Hits the Earth***

[You wouldn\'t hear it coming]{.underline}. A 100-ton extraterrestrial
object hits the Earth at hypervelocity, more than 11 kilometers per
second, and sometimes as fast as 20-25 km/sec. (Smaller objects slow
down or are destroyed because of air resistance.) That\'s faster than
sound (about 300 m/sec).

The object comes to a stop in about one hundredth of a second.

1\. There is a [rapid release of a tremendous amount of kinetic
energy]{.underline}. What would be the effect of that rapid release of
energy on the solid earth, the air, and living things? What forms might
that energy take, and where might it go? Respond here:

Effects on rocks and soil:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Effects on the shape of the land (topography):
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Effects on the air:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Effects on living things:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

2\. The energy release creates a [shockwave]{.underline} stronger than
any material it hits. What could be the effects of that shockwave on the
rocks and soil, and on large bodies of water? Respond here:

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

3\. What would be the effects of impact on the object itself? Would it
remain intact (in one piece)? Respond here:

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Landsat 7 Educational Activity Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Finding Impact Craters with Landsat

Student Name:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Class Period: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Student Reading for Step 2:**

**Known Effects of Impact Events**

***When an object from space hits the Earth...***

-- There\'s a huge [explosion]{.underline}.

-- The impact makes a [big hole]{.underline} or crater with a raised
[rim]{.underline} and *sometimes* a central [peak]{.underline}.

> The hole is many times larger than the impacting object.

-- There is a [rapid release of a tremendous amount of kinetic
energy]{.underline} as the object comes to a stop in about one hundredth
of a second.

\- The impact releases [extreme heat]{.underline}. Usually, the [object
itself is vaporized]{.underline}. Sometimes it melts completely and
mixes with melted rocks at the site.

-- If the impact occurs in water, a whole [column of water is
vaporized]{.underline}.

-- The impact also produces a super-hot blastwave -- a
[shockwave]{.underline} -- that radiates rapidly outward from the impact
point through the target rocks at velocities of a few kilometers per
second.

> The shockwave is stronger than any material on Earth. It [deforms
> rock]{.underline} in ways that are characteristic of an impact event.
> No other event on Earth deforms rock in these ways.

-- Tiny glass droplets can form during the rapid cooling of molten rock
that splashes into the atmosphere.

-- Large impacts also [crush, shatter, and/or fracture the target
rocks]{.underline} extensively beneath and around the crater. [See
diagram]{.underline} at:
http://cass.jsc.nasa.gov/expmoon/science/craterstructure.gif

-- [Hot debris is ejected]{.underline} from the target area, and falls
in the area surrounding the crater. Close to the crater, the ejecta
typically form a thick, continuous layer. At larger distances, the
ejecta may occur as discontinuous lumps of material.

-- Large impact events can [blow out a hole in the
atmosphere]{.underline} above the impact site, permitting some impact
materials to be dispersed globally by the impact fireball, which rises
above the atmosphere. The resulting extensive dusk and smoke clouds can
cause [darkness]{.underline} lasting for a year.

-- Special carbon molecules called Buckminsterfullerenes or
(Bucky-balls, after Buckminster Fuller) can travel to the Earth in the
impactor. They can hold special gases called \"noble\" gases that are
indicators of extraterrestrial origin.

-- Large impacts can trigger [earthquakes]{.underline} and initiate
[volcanic eruptions]{.underline}.

-- The heat ignites [fires]{.underline}, and they may rage across a
large region.

-- Impact events can alter the [chemical composition of the
atmosphere]{.underline}. The extreme heat can generate large amounts of
nitrogen oxides (NOx). NOx is easily transformed into nitric acid,
resulting in [acid rain]{.underline}.

**More About ...**

## More About Impact Events in General

Impact craters are geologic structures formed when a large meteoroid,
asteroid or comet smashes into a planet or a satellite.

A very large number of meteoroids enter the Earth\'s atmosphere each
day, amounting to more than a hundred tons of material. They are almost
all very small, just a few milligrams each. Only the largest ones ever
reach the surface. The average meteoroid enters the atmosphere at
between 10 and 70 km/sec. All but the very largest are quickly
decelerated to a few hundred km/hour by atmospheric friction, and they
hit the Earth\'s surface with very little fanfare. However meteoroids
larger than a few hundred tons are slowed very little; only these large
(and fortunately rare) ones make craters.

All the inner bodies in our solar system have been heavily bombarded by
meteoroids throughout their history. The surfaces of the Moon, Mars and
Mercury, where other geologic processes stopped millions of years ago,
record this bombardment clearly. On the Earth, however, which has been
even more heavily impacted than the Moon, craters are continually erased
by erosion and redeposition as well as by volcanic resurfacing and
tectonic activity. Thus only about 120 terrestrial impact craters have
been recognized, the majority in geologically stable areas of North
America, Europe and Australia. Spacecraft imagery has helped to identify
structures in more remote locations that can be explored for positive
identification.

**More About the Energy Released by Impact**

Energies of impact are almost incomprehensibly large. They come chiefly
from the kinetic energy of the impacting object. An object only a few
meters across carries the kinetic energy of an atomic bomb as it strikes
another object at high velocity. The impact of an object only a few
kilometers across (smaller than many known asteroids and comets) can
release more energy in seconds than the whole Earth releases (through
volcanism, earthquakes, tectonic processes, and heat flow) in hundreds
or thousands of years.

**More About Extraterrestrial Objects in the Solar System**

Thousands, possibly millions, of objects move throughout the solar
system, orbiting the Sun. They range from microscopic dust particles to
objects tens of kilometers across. Each object moves in its own orbit.
We don\'t know how often they have hit the Earth in the past.

**More About Impact Velocity**

The minimum impact velocity for collisions with Earth is 11.2 km/s. This
is equal to the escape velocity for an object launched into space from
Earth\'s surface.

**More About the Sizes of Craters**

Objects of less than half a kilometer in diameter can make craters 10 km
in diameter.

## More About Crater Shapes

Nearly all impact events result in circular craters. In rare cases where
the angle of impact was very low (0-10 degrees from the plane of the
horizon), craters can be ovoid in shape.

**More About Finding Impact Craters on the Ground**

When looking for impact craters in satellite images, first pay attention
to circular features in topography or bedrock geology. Look for lakes,
rings of hills, or isolated circular areas.

On the ground, look for changes in the physical properties of the rocks
in and around impact structures. Fractured rock is less dense than
unaltered target rock around the structure. Also look ejecta and shocked
rock fragments on the original ground surface outside the crater, and
for fragments of the meteorite.

Landsat 7 Educational Activity Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Finding Impact Craters with Landsat

Student Name:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Class Period: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Student Worksheet for Step 4:**

**[Describing Satellite Images of Possible Impact Craters]{.underline}**

**Part I.** Consider what effects an impact event might have, and
**describe those effects below**. Though you are working in groups for
this step of the activity, each student must complete this worksheet.

A. [The object itself]{.underline}: Would you expect to see any evidence
of the object itself in a satellite image? What evidence might you find?

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

B. [Shape of the land:]{.underline} What kinds of changes would that
impact make to the shape of the land where it hit, and all around?

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

C. [Effects of Time]{.underline}: What kinds of changes will occur to
the impact site over time? Remember that some changes are fast, and some
are slow.

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­

D. [What else]{.underline} might you see in these satellite images that
could help you learn about an impact crater?

­­­­­­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Part II. As a group, study all of the satellite images.** Below are
their fake names (to use until you\'ve identified them yourselves as
impact craters or something else):

> AOR
>
> Latitude: N 19° 6\'
>
> Longitude: E 19° 15\'
>
> Size: 12.6 km in diameter
>
> ELG
>
> Latitude: N 67° 30\'
>
> Longitude: E 172° 5\'
>
> Size: 18 km in diameter
>
> HGH
>
> Latitude: N 75° 22\'
>
> Longitude: W 89° 41\'
>
> Size: 20 km in diameter
>
> MAN
>
> Latitude: N 51° 23\'
>
> Longitude: W 68° 42\'
>
> Size: 72 km in diameter
>
> MSH
>
> Latitude: N 46° 16\'
>
> Longitude: W 122° 12\'
>
> Size: several km in diameter
>
> RCH
>
> Latitude: 21°04\'N
>
> Longitude: 11°22\'W
>
> Size: 38 km in diameter
>
> SCH
>
> Latitude: N 37deg 20\' 36.1\"
>
> Longitude: W 116deg 33\' 59.9\"
>
> Size: About 300 m in diameter

*[You need to know that...]{.underline}*

 All of these satellite images show [the Earth\'s land
surface]{.underline}, not another planet\'s surface, and not the
Earth\'s atmosphere. No hurricanes or tornadoes appear in these images.

 The colors in these images are [false colors]{.underline}. White
isn\'t always snow; lakes often appear black; vegetation is sometimes
red.

 All of these landforms are large. One is 300 m in diameter, and the
others are 1 km in diameter or larger. Most of them 10-90 km in
diameter.

 [Aliens]{.underline} from other parts of the universe had nothing to
do with creating the landforms in these images.

 If you see [a letter or a face]{.underline}, it\'s just an accident of
nature.

 [People]{.underline} sometimes make large craters with explosives or
large mining equipment.

 [Multiple Impacts]{.underline}: Sometimes impacts come in twos or
threes. It\'s rare, but it can happen when a comet or asteroid breaks
into a couple of large pieces just before it strikes the Earth.

Part III. As a group, now choose two of the images you find most
interesting, and prepare to describe them to the class as directed by
your teacher.

A. [Circle the name]{.underline} or names of the one or two landform(s)
your group has chosen to describe for the class. Write next to it if you
think it is an impact crater or some other kind of landform.

> AOR ELG HGH MAN MSH RCH SCH

B. [What evidence]{.underline} do you see in the satellite image that
your landform is or is not an impact crater? Describe it here:

­­­­­­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­­­­­­­­­\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Come to agreement as a group about whether or not the image you\'ve
chosen is or is not an impact crater, and why.

Landsat 7 Educational Activity

Finding Impact Craters with Landsat

**Teacher Reference for Step 5:**

**[The Landforms Identified]{.underline}**

[Aorounga]{.underline}

Impact Crater? Yes

Latitude: N 19° 6\'

Longitude: E 19° 15\'

Age: 345 million years

Size: 12.6 km in diameter

Location: Sahara Desert of northern Chad, Africa

Kind of Image: Spaceborne Imaging Radar-C/X-Band Synthetic Aperture
Radar (SIR-C/X-SAR)

Description: An object less than 1 kilometer wide made this crater 7-10
miles wide. The original crater was buried by sediments, which were then
partially eroded to reveal the current ring-like appearance. The dark
streaks are deposits of windblown sand that migrate along valleys cut by
thousands of years of wind erosion. The dark band in the upper right of
the image is a portion of a proposed second crater. Scientists are using
radar images to investigate the possibility that Aorounga is one of a
string of impact craters formed by multiple impacts.

20,000-30,000 years ago, the area that is now the Sahara Desert was a
wetland. Different kinds of forces were shaping this crater then.

360 million years ago, the Earth was undergoing a period of mass
biological extinction. By way of comparison, the impact that scientists
believed wiped out the dinosaurs 65 million years ago involved an
asteroid or comet 10 times larger than the one that broke up to form the
craters in Chad.

##### El\'gygytgyn 

Impact Crater? Yes

Latitude: N 67° 30\'

Longitude: E 172° 5\'

Age: 3 - 4 million years

Size: 18 km in diameter

Location: Northeastern Siberia

Kind of Image: Landsat 7

Description: This impact crater has been filled in by a lake.

# Haughton

Impact Crater? Yes

Latitude: N 75° 22\'

Longitude: W 89° 41\'

Age: 23 million years

Size: 20 km in diameter

Location: Devon Island, Nunavut, in the Canadian high Arctic

Kind of Image: NASA\'s Landsat 7

Description: Although Haughton Crater has undergone substantial erosion,
many of its surviving geologic features are exceptionally well
preserved. The good state of preservation is due mostly to the crater\'s
geographic setting. Erosion in the polar desert of the high Arctic is
particularly sluggish due to the low amount of liquid water and the
presence of continuous permafrost. The absence of any substantial
vegetation cover also limits the weathering of surface materials, while
it optimizes the site\'s exposure for geologic surveys from the ground
and by remote sensing.

The impact event punched through the entire stack of Paleozoic sediments
present at the time and excavated material from a depth of over 1.7 km,
biting into the gneissic basement.

[Manicougan]{.underline}

Impact Crater? Yes

Latitude: N 51° 23\'

Longitude: W 68° 42\'

Age: 214 million years

Size: 72 km in diameter now; 100 km in diameter when created

Location: northern Quebec, Canada

Kind of Image: NASA\'s Multi-angle Imaging Spectroradiometer (MISR)

Description: Scientists have proposed that impact of an asteroid of
about 5 km in diameter created this crater, which was originally about
100 km in diameter. The initial crater rim has disappeared. A broad
central uplift persists. Construction of a hydroelectric dam downstream
from the crater allowed water to fill the surrounding depression,
creating a lake that forms a ring around the central part.

The Manicougan crater is composed of large pieces of rock embedded in
finer grained material rock (\"impact-brecciated\" rock). Geologists
have estimated the crater\'s age by studying the ratios of various
radioactive elements in the rock. The lake is bounded by
erosion-resistant metamorphic and igneous rocks, and shock metamorphic
effects are abundant in the target rocks of the crater floor.

The Manicougan impact event occurred toward the end of the Triassic
period. At that time the Earth experienced a mass extinction event
involving the loss of roughly 60 percent of all species. Some scientists
believe the impact may have been responsible for this mass extinction.

######## Mount St. Helens

Impact Crater? No. Mount St. Helen\'s is a volcano.

Latitude: N 46° 16\'

Longitude: W 122° 12\'

Age: probably less than 1 million years

Size: Several km in diameter

Location: South central part of the State of Washington, northwestern
United States

Kind of Image: NASA\'s Landsat 7

[Richat]{.underline}

Impact Crater? No. Richat is a product of erosion.

Latitude: N 21°04\'

Longitude: W 11°22\'

Age: Modern age

Size: 38 km in diameter

Location: Central Mauritania, northwest Africa

Kind of Image: NASA photograph taken by astronaut on the Space Shuttle

Description: Richat is a depression or pit about 100 m deep, in which
there is a dome of rock. The rock is actually different kinds of rock in
layers, several hundred million years old. Some kinds of rock erode
faster than others. Made of different materials, the layers of rock have
eroded at different rates, creating a series of concentric ridges.
Fields of sand surround Richat and are encroaching into the southern
part of the structure.

Researchers once thought Richat was an impact crater. But its flat
middle and lack of shock-altered rock indicate otherwise. A volcanic
eruption couldn\'t have formed it, because there\'s no dome of igneous
or volcanic rock. Why Richat is nearly circular, nobody knows.

[Schooner]{.underline}

Impact Crater? No, Schooner is manmade.

Latitude: N 37deg 20\' 36.1\"

Longitude: W 116deg 33\' 59.9\"

Age: 20^th^ century

Size: About 300 m in diameter

Location: Nevada, U.S.

Kind of Image: IKONOS (privately-owned satellite); 1-meter resolution

Description: Nuclear testing resulted in the Schooner crater.

Landsat 7 Educational Activity

Finding Impact Craters with Landsat Due Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Student Name:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Class: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Student Worksheet for Step 6:**

**Questions You Would Ask**

**on a Field Expedition to a Possible Impact Crater**

Identifying what might be an impact crater in a satellite image is only
the first step in identifying it with 100 percent certainty. That
requires people making a field expedition to gather and study evidence
at the site itself.

Field expeditions cost money. Getting money nearly always requires
writing excellent grant proposals. You have to prove you understand the
science and know what you\'re doing before people will give you the
money to do it.

**[Your task]{.underline}** is to write a series of questions you would
use to guide a field expedition to determine whether or not a given
landform was an impact crater.

[You will do well on this learning assessment if you]{.underline}:

> -- [Show evidence]{.underline} that you have a full and complete
> understanding of how an impact event can shape the land, soil, and
> surrounding rocks, as well as the atmosphere and living things;
>
> -- Use terminology [accurately]{.underline};
>
> -- Explain your ideas in ways that [makes sense]{.underline};
>
> -- Use [complete sentences]{.underline}.

Landsat 7 Educational Activity

Finding Impact Craters with Landsat

**Student Learning Assessment Rubric**

**LEVEL 4**

There is evidence in this response that the student, using analysis, has
a full and complete understanding of how impact events have shaped the
land, atmosphere, and living things.

-   The response synthesizes information to provide a complete
    description of the known effects of an impact event on the Earth
    system.

-   Ideas are well integrated.

-   The response uses accurate terminology to explain scientific
    principles.

**LEVEL 3**

There is evidence in this response that the student, using analysis, has
a good understanding of how impact events have shaped the land,
atmosphere, and living things.

-   The response synthesizes information to provide a complete
    description of the known effects of an impact event on the Earth
    system.

-   Ideas are reasonably well integrated.

-   The response uses mostly accurate terminology to explain scientific
    principles.

**LEVEL 2**

There is evidence in this response that the student has a basic
understanding of how impact events have shaped the land, atmosphere, and
living things.

-   The response provides descriptions of some known effects of an
    impact event on the Earth system.

-   Ideas are reasonably well integrated.

-   The response uses limited accurate terminology to explain scientific
    principles.

**LEVEL 1**

There is evidence in this response that the student has limited
understanding of how impact events have shaped the land, atmosphere, and
living things.

-   The response provides partial descriptions of one or two effects of
    an impact event on the Earth system.

-   Ideas are not well integrated.

-   The response makes little or no use of accurate terminology to
    explain scientific principles.

**LEVEL 0**

There is evidence that the student has no understanding of how impact
events have shaped the land, atmosphere, and living things.

The response is completely incorrect or irrelevant, or there is no
response.

Landsat 7 Educational Activity

Finding Impact Craters with Landsat

# **Extensions**

1\. Few Craters on the Earth.

> Craters cover the Moon\'s surface; we can see them easily with a
> telescope. Why do we find few craters on Earth, and why is it so hard
> to find them?
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

2\. Craters in the Sea.

> Only a handful of impact craters have ever been discovered under the
> sea. One reason is that the sea floor is harder to get to and to study
> than places on land. There is another reason. What is it?
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

­­

> ­­

3\. Craters Around the Globe.

> Visit a world map of impact craters at:
> http://gdcinfo.agg.emr.ca/crater/world_craters_e.html
>
> Have more impact craters been discovered in some places than in
> others? Where are these \"clusters\" of craters? Why are they where
> they are and not somewhere else?
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> ­­

4\. Impact on Jupiter.

> Jupiter was hit by fragments of an object designated Comet
> P/Shoemaker-Levy 9 in 1994. \[http://www.jpl.nasa.gov/sl9/\] No
> craters were made by this impact. Why not?
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

5\. Impacts Elsewhere in the Solar System.

> Would you expect to find impact craters on solid bodies in the rest of
> the solar system? Why or why not?
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_­­
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_