voyage: a journey through our solar system grades 5-8 ... · pdf filejourney through the...

Voyage: A Journey Through Our Solar System

Grades 5-8

Lesson 10: Impact Craters: A Look at the Past

On October 17, 2001, a one to ten billion scale model of the Solar System was permanently installed on the National Mall in Washington, DC. The Voyage ex-hibition stretches nearly half a mile from the National Air and Space Museum to the Smithsonian’s Castle Building. Voyage is a celebration of what we know of Earth’s place in space and our ability to explore beyond the confines of this tiny world. It is a celebration worthy of the National Mall. Take the Voyage at www.voyageonline.org, and consider a Voyage exhibition for permanent installation in your own community.

This lesson is one of many grade K-12 lessons developed to bring the Voyage experi-ence to classrooms across the nation through the Journey through the Universe pro-gram. Journey through the Universe takes entire communities to the space frontier.

Voyage and Journey through the Universe are programs of the National Center for Earth and Space Science Education, Universities Space Research Association (www.usra.edu). The Voyage Exhibition on the National Mall was developed by Challenger Center for Space Science Education, the Smithsonian Institution, and NASA.

Copyright June 2006

JOURNEY THROUGH THE UNIVERSE�

Lesson 10: Impact Craters: A Look at the Past

Lesson at a Glance

Lesson OverviewIn this lesson, students discover that it is possible to learn a lot about objects in the Solar System and their history, as well as the history of the entire Solar System, just from looking at the craters on their surfaces. Students simulate how impact craters are formed, and how craters can look different based on the amount of energy they had during impact. Students then examine pictures of cratered surfaces of other worlds in the Solar System and discover that impact craters can provide a lot of information about a world’s history, and the history of the entire Solar System.

Lesson DurationTwo 45-minute class periods

Education Standards

National Science Education StandardsCore StandardStandard D2: The earth processes we see today, including erosion, movement of lithospheric plates and changes in atmospheric compo-sition, 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.

Related StandardStandard D1: Land forms are the result of a combination of constructive and destructive forces. Constructive forces include crustal deformation, volcanic eruption, and deposition of sediment, while destructive forces include weathering and erosion.

AAAS Benchmarks for Science LiteracyBenchmark 4C2: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, which act to level mountain ranges.

JOURNEY THROUGH THE UNIVERSE �

Impact Craters: A Look at the Past

Essential Questionw What can craters tell us about the history of objects in the

Solar System?

ConceptsStudents will learn the following concepts:

w Impact craters are depressions or pits on the ground formed by impacts by objects falling from space.

w The surface of the Moon has more impact craters than the Earth because there are processes on the Earth that erase and retard this type of cratering.

w Scientists can tell a lot about an object simply by studying the craters on the surface of objects.

ObjectivesStudents will be able to do the following:

w Examine impact craters and determine some properties of the object which created it.

w Decipher the history of objects in the Solar System based on the nature of its craters.


Science Overview

What is an Impact Crater?Impact craters are geologic structures formed when a meteoroid, aster-oid, or comet smashes into a planet, a moon, or another Solar System object with a solid surface. A meteoroid is a piece of stone-like or metal-like debris that travels in outer space. Most meteoroids are no bigger than a pebble. Large meteoroids are believed to come from the asteroid belt. This is a large belt of objects that are in orbit around the Sun between Mars and Jupiter. Some of the smaller meteoroids may have come from the Moon or Mars. When a meteoroid hits the Earth’s surface, it is called a meteoritre. Comets are sometimes called dirty snowballs or “icy mudballs.” They are a mixture of ices (both water and frozen gases) and dust that for some reason did not get incorpo-rated into planets when the Solar System was formed. Most comets orbit the Sun in a path that comes close to the Sun and then travel far beyond the orbit of Pluto.

All the inner planets (Mercury, Venus, Earth, and Mars) in the Solar System have been heavily bombarded by meteoroids throughout their history. This may also be true of Pluto (currently the outermost defined planet), since it is a solid planet like the inner ones, even though we do not know for sure at present time, since there are not sufficiently good pictures of Pluto to see features on its surface. Craters can also be found on the moons, asteroids, and possibly even on comets. It appears that most objects in the Solar System with a solid surface show evidence for meteoroid bombardment at some point in their history.

On Earth craters are continually erased by erosion as well as by volcanic resurfacing and tectonic activity. Thus only about 160 terrestrial impact craters have been recognized, the majority in geologically stable areas of North America, Europe, southern Africa, and Australia, where most ex-ploration has taken place to date. Spacecraft orbital imagery has helped to identify structures in more remote locations for further investigation in the future. As an example, scientists found the Chicxulub crater near Cancun in Mexico using seismic monitoring equipment designed to search for oil. Much of the crater lies under the ocean, and all of it is hidden under 65 million years’ worth (or about 1 km; 0.6 miles) of sediment. The crater is estimated to be 145-180 km (90-110 miles) wide. The Chicxulub impact is thought to have triggered a mass dinosaur die-off, through massive, long-term environmental changes. However, it is rare that impacts occur on Earth. The meteoroid would need to be large enough not to be vaporized as it entered Earth’s atmosphere. In addition, the orbit of a meteoroid would need to cross the Earth’s orbit at the same time as the Earth is at that same position.



Lesson at a Glance

Science Overview

Conducting the Lesson

Resources

Crater PartsWhen an object slams into a planet, a moon, or another solid body in the Solar System, it hits the surface very hard and causes the energy of the impacting object to be transmitted to the ground by a shock wave, and much of the object vaporizes during the process. The object that hits the planet is called an impactor. They create a shock wave; also, the way a crater is created depends on the size of the impactor—small impactors do not involve shock waves and a creation of a great crater; rather, they excavate a crater only slightly larger than the impactor; the sequence here describes a very high-velocity impact, where the impac-tor has not been slowed down much by the atmosphere. The shock waves expanding from the point of impact cause rocks and dust to fly away from the impact side and excavate a crater. The resulting impact forms a usually circular depression in the ground, which is called a crater. The base of a crater is called the floor, whereas the sides are called the wall. At the top of the crater wall is the crater’s rim. When a meteoroid strikes a planet, debris is typically ejected from the site of the impact. This debris is called ejecta. Sometimes rays can be seen surrounding a crater. The ray system is created by fine ejecta coming from the crater (and not all ejecta), and only occurs on objects that do not have a significant atmosphere. See Fig. 1 for an illustration of the parts of the crater.

Walls – The sides of the crater bowl. Walls can be very deep, depending on the severity of the impact. If a crater has shallow walls, then the crater may have been filled or eroded somehow since its formation.

Floor – The bottom part of the impact site. It may be the shape of a bowl, or it may be flat. This part is lower than the sur-rounding surface.

Rim – The edge of the crater; the rim is usually the highest part of the crater.

Ejecta – The debris that shoots, or ejects, out of the impact site when the crater forms. There is a lot of ejecta close to the crater, so the layer of eject is thick there. The ejecta gets thinner the farther away it is from the crater. The impact creates debris as the shock wave crushes, heats, and melts the rock.

Rays – The bright streaks that start at the rim of the crater and extend outward. Rays are created by fine ejecta coming from the crater and are only found on worlds where there is no sig-nificant atmosphere (e.g., on the Moon but not on Earth).


Central Peak – A small mountain that may form at the center of the crater in reaction to the force of the impact. Only large craters can have a central peak. The size at which craters can have central peaks depends on the size of the world. For ex-ample, on the Earth, craters larger than 2-4 km (1.2-2.5 miles) can have central peaks, while on the Moon, the crater must be larger than 15-20 km (9-12 miles) in diameter.

What Changes the Shape of a Crater?Initially, craters have a crisp rim and blankets of ejecta around the sides. On the Earth, actions of wind, water, lava flows, and plate tectonics can alter the appearance of a crater. Wind can blow away debris around the crater. Rivers and floods can erode the crater’s walls and rim, or the crater may be filled with water to form a lake. Lava flows can fill in the crater and make the rim smoother. Another impactor may come along and create a new crater inside an old crater. Other impactors can partially or completely destroy an older crater. Some of these effects can also operate on other worlds in the Solar System, depending on the properties of the world. For example, there is no wind or water on the Moon to erode the craters formed there, but one can see craters on the Moon that have been filled with lava, or see craters where new craters have been created on top of old ones.

Craters and Surface AgeThe older a surface is, the more time impactors have had to hit it. Really old surfaces have so many craters that it would be difficult to notice if another impactor hit it. Little of the surface is smooth. Most cratering took place right after the planets and moons formed, when there was a lot of debris left over from the formation of planets and other large objects in the Solar System. Places like the Earth’s Moon and the planet Mercury have heavily cratered, old surfaces.

However, the situation is a bit more complicated if the object has a sub-stantial atmosphere. If an atmosphere were present, most of the small meteoroids would “burn up” before hitting the surface. The friction of the atmosphere heats up the objects flying through it, and this process completely destroys most of the smaller meteoroids. In addition, there are other factors that can influence the number and the type of craters on an object. If there is a substantial atmosphere, there are probably winds that would tend to erode craters or fill them with dust (like on Earth or Mars). If the object has water, volcanoes, or is subject to the action of plate tectonics, the craters would have been covered with water and sediment, covered with dust and rock, or destroyed by the movement of the surface, respectively.



Lesson at a Glance

Science Overview


Resources

Figure 1.(Image credit: Part of Apollo 17 Metric photograph AS17-2923.)

The amount of energy involved in the impact depends upon the size of the impactor and the speed with which it hits the surface. The larger the impactor (more energy) the larger the crater. In addition, for two impactors of equal size, the crater would be larger for the one that hit with the greater speed (more energy).

Craters on the Moon range in size from over 300 km (190 miles) in di-ameter (larger than the state of Connecticut) to smaller than the head of a pin. Impact structures greater than 300 km (190 miles) are called impact basins, rather than craters, the dark regions of the Moon called

walls

floor

rim

ejecta

rays

central peak


maria, are examples of these large impact basins. Because there is no weather on the Moon, and little geologic activity, the only way to erode an existing crater is to cover it with more impacts or more debris from impacts. Young craters have sharp rims and are relatively deep. Older, more worn craters are usually shallow and have less distinct rims than newer craters. Scientists can estimate the relative ages of portions of the Moon by counting the number of impact craters present. The more craters, the longer the surface has been exposed to bombardment by meteoroids. Look at the Moon through a pair of binoculars, and you will see many craters. In fact, it is hard to find any place on the Moon where there are not any craters.

Impacts on EarthAs stated previously, craters are formed when a large meteoroid, as-teroid or comet smashes into a planet or its moon. Earth’s atmosphere protects us from most small objects that enter it. However, once in a while, a large object collides with Earth. The Chicxulub crater (men-tioned earlier) was formed when a meteoroid hit Earth near Cancun, Mexico, 65 million years ago. Another example is the Meteor Crater (also known as Barringer Crater) in Arizona that was formed by an-other meteoroid collision about 50,000 years ago. These large collisions happen only rarely. However, it is important for astronomers to track large meteoroids, because a large impact could be catastrophic to life on Earth. There are many astronomers around the world that are looking for objects that may pass near the Earth in the future.

Impacts on Other WorldsIn 1994, comet Shoemaker-Levy 9 crashed into Jupiter, creating dis-turbances in its atmosphere that were visible for months afterwards. The comet’s orbit had been disturbed when it got too close to Jupiter to resist its gravitational pull. In fact, the pull was so strong that the comet was split into at least 21 discernible fragments two years before it plunged into Jupiter’s atmosphere. The largest of these fragments was 4 km (2.5 miles) in diameter, and upon arrival produced an explo-sion the equivalent of 6,000,000 megatons of TNT, or about 75 times the estimated nuclear arsenal of the entire world during the height of the Cold War. This was the first time scientists were able to witness such a collision in the Solar System. Many available instruments on Earth and in space (Hubble Space Telescope, Galileo spacecraft) were used to capture images of this amazing event. Since Jupiter does not have a solid surface, no crater was produced. However, it is an example of an impact on another world.



Lesson at a Glance

Science Overview


Resources

By studying the properties of the impact craters on different worlds (or different parts of a world), you can deduce something about the his-tory of that object, or even about the history of the whole Solar System (such as there was a lot of debris left over from the formation of the Solar System, giving rise to the heavy meteoroid bombardment early in Solar System’s history).

JOURNEY THROUGH THE UNIVERSE10


Warm-Up & Pre-AssessmentTeachers will lead a discussion with the students about why there are hardly any craters easily visible on Earth, but many seen on the Moon.

Teacher Materialsw Picture of the Moon and the Earth found

in the back of the lessonw Overhead projector

Preparation & Procedures1. Make an overhead transparency of the picture of the Moon and the

Earth found in the back of the lesson. Project this onto a screen for the entire class to see.

2. Ask students to list ways in which the Moon looks different from the Earth. Some examples may be the lack of colors on the Moon, the lack of clouds on the Moon, and that the Moon has many craters. Make sure students understand what impact craters are.

3. Lead a discussion with the students as to why the two worlds look so different, even though they are located at the same distance from the Sun in the Solar System. Focus the discussion on craters. Ask students to hypothesize why there are craters on the surface of the Moon, but few visible on the surface of Earth.

JOURNEY THROUGH THE UNIVERSE 11



Warm Up &Pre-Assessment

Activity 1: Creating Craters

Activity 2:Craters in the Solar System

Lesson Wrap-Up

Resources

Lesson at a Glance

Science Overview

Notes:

JOURNEY THROUGH THE UNIVERSE1�


In this activity, students will simulate crater impacts by dropping pebbles or marbles into a pan of flour and cocoa. Students will identify the characteristics of impact craters and compare them to the picture of a lunar crater.

Student Materials (per pair of students)w Student Worksheet 1w Lunar Crater Imagew 1 pie pan (approximately 9 in)w Two pebbles or marbles of different sizes w Scale to measure mass of marbles w A bag of flour or a box of corn starchw Metric rulerw Sifterw Newspaper to cover the work surface w Powdered cocoa (about one sandwich-sized plastic bag full) w Meter stickw Calculator (optional)

Preparation & Procedures1. Make copies of Student Worksheet 1 and the Lunar Crater Image

found in the back of the lesson.

2. Discuss with the class what an impact crater is and how it is formed. You can use the following questions to lead your discussion:

There are a lot of pieces of rock floating around in space—do they ever hit anything? (Desired answer: yes) What evidence do we have that this has happened? (Desired answer: we see impact craters, for example on the Moon) What happens to the piece of rock (we call this the impactor) that hits the Moon when it impacts? (Desired an-swer: it can hit with such a speed that it is vaporized) Does everything hit the Moon with the same amount of energy? (Desired answer: probably not) What would make something hit the Moon with a different amount of energy? (Desired answer: if the impactor was bigger or moving faster it might hit with more energy) Years later, if we have no remnants of the impactor, but only the impact crater, how could we tell the amount of energy that impactor had when it hit the Moon? (Desired answer: the impact crater might look different if it has been hit with different impactors with varying energies) How could

JOURNEY THROUGH THE UNIVERSE 1�






Lesson Wrap-Up

Resources

Lesson at a Glance

Science Overview

we investigate what those impact craters might look like? (Desired answer: we can create a model and create impact craters, and examine them to see what they look like based on different kinds of impacts with varying energy) That’s exactly what we’re going to do!

3. Divide students into pairs and pass out Student Worksheet 1 and the student materials.

4. When students have completed the activity, give them a copy of the Lunar Crater Image so that they can answer the questions on their worksheet.

Reflection & Discussion1. Discuss the features of impact craters with students. Discuss with

students the formation of impact craters and their features (rays, rim, ejecta, central peak).

2. Ask students to discuss how their craters looked different based on the amount of energy the impactor had when it hit.

3. Ask students to pretend that they are scientists who are seeing a crater on the Moon or another world for the very first time. Can they tell what the impactor was like based on what the crater looks like? (Desired answer: not completely, because the size of the crater depends on the velocity and the size of the impactor, not just the mass. However, as a general rule, the larger and more massive the impactor, the larger the cra-

ter. Therefore, scientists can determine the approximate size of impactors based

on crater size.) Discuss with the students the difference

between size (diameter, for example) and mass. Both are varied simul-taneously in their ex-periment, but they are actually different factors. Crater size, however, depends on

both mass and size.

Teaching Tip

What students do in this activity is dif-ferent than real cratering events in some ways.

When a crater is formed on a planetary surface, the energy of the impactor can break apart—even vapor-

ize—the impactor. In addition, the energy of a crater is determined by its mass and its velocity when it reaches Earth, but in this activity students calculate the potential energy from the height dropped. You may want to

make sure the students understand the differences between their model and real impact craters

at the end of the activity.

Teaching Tip

If corn starch is used instead of flour in this activity it will store lon-

ger and can be used again.


Assessment Criteria for Activity 1

4 Pointsw Student completed Student Worksheet 1 and gave appropriate reasons for

the answers to the questions.w Student answered the two Transfer of Knowledge questions correctly and

gave appropriate reasons for the answers.

3 Pointsw Student completed most of Student Worksheet 1 and gave appropriate

reasons for the answers to the questions.w Student answered the one Transfer of Knowledge question correctly and gave

appropriate reasons for both answers (this places emphasis on supporting conclusions, no matter whether correct or incorrect).

2 Pointsw Student completed some of Student Worksheet 1 and gave appropriate

reasons for the answers to the questions.w Student answered the two Transfer of Knowledge questions and gave ap-

propriate reasons for their answers, even if the answers were incorrect.

1 Pointw Student completed some or all of Student Worksheet 1, but did not give ap-

propriate reasons for the answers to the questions.w Student answered the two Transfer of Knowledge questions correctly, but did not

give appropriate reasons for their answers.

0 Pointsw No work completed.







Lesson Wrap-Up

Resources

Lesson at a Glance

Science Overview

Transfer of KnowledgeHave students complete the Transfer of Knowledge section in Student Worksheet 1. Here, they are asked to compare two impactors that caused two craters on the Moon.

Placing the Activity Within the LessonAsk student to blow gently on their impact craters (or ask them to imagine what would happen if they were to blow on their impact cra-ters). What happened? (Desired answer: they erode away) Ask students to think about why we can see impact craters on the Moon if they are so easily destroyed. Ask them to think about what sorts of conditions may happen on other worlds that would help to erase impact craters that once were there. This activity helped students understand the nature of impact craters, but in the next activity, they will be looking at pictures of surfaces on other worlds, and they will be asked why some impact craters are still around while others have disappeared.

ExtensionsHave students create a graph of Energy vs. Size of Impact Crater. Help them analyze it to see that the correlation is positive. You can also create graphs of impactor mass vs. impact crater or impactor size vs. impact crater.

Notes on Activity 1:


Activity 2: Craters in the Solar System

In this activity, students will examine impact craters on different worlds in the Solar System and discover that the craters can tell us a lot about the world on which they formed.

Student Materials (per pair of students)w Student Worksheet 2

Preparation & Procedures1. Ask students to recall the Warm-Up & Pre-Assessment activity

where they looked at the Moon and the Earth and compared the two worlds. The Moon clearly has more craters on its surface than the Earth. Ask students why they think this is; does it make sense that things hit the Moon more than the Earth, even though they are located at approximately the same place in the Solar System? (Desired Answer: no; some students may think that things actually do hit the Moon more often than the Earth. Ask them to explain why this would be the case and to back up their answer. Then move on and ask for other possibilities.)

Are there any other explanations as to why there are not as many craters on the Earth as on the Moon? Is there anything that the Earth has that would protect itself from getting hit that the Moon does not have? (Desired answer: an atmosphere).

In fact, many smaller objects burn up in Earth’s atmosphere due to friction with air and they never reach the ground to make a crater. For this reason, do you think the craters that do appear on Earth are very big or very small? (Desired answer: they are very big, because all of the very small things that hit the Earth burn up in its atmosphere, while big objects that hit the Earth may burn partially, but they are big enough to make it through the atmosphere to the ground.)

Is there anything that the Earth has that will not let craters stick around that the Moon does not have? (Desired answer: Earth has weather that can erode the craters, like wind and rain, as well as lakes and oceans, volcanoes, and plate tectonics)

What other reasons could there be for why there are not as many craters on Earth? (Desired answer: Earth has oceans; if something hits the ocean, a crater will not be visible on the surface but only on the ocean floor, which may quickly be eroded away by the water)







Lesson Wrap-Up

Resources

Lesson at a Glance

Science Overview

2. Tell students that scientists describe surfaces like Earth as “young” and surfaces like the Moon as “old.” Why do they think this is the case? (Desired answer: the craters on the Moon have been around for a long time, because there is very little there to erase them or to “renew” the surface. The Earth’s surface gets renewed all the time because of the activity on the surface; the craters on the Earth are probably young, because the older ones have been erased, or they are in regions where significant erosion has not happened for one reason or another.) Some worlds may have very young surfaces, some may be very old. Some worlds may have parts that are one or the other.

3. Pass out Student Worksheet 2 to each pair of students, and tell them that they will be looking at cratering on other worlds in the Solar System, and that they will have to come up with conclusions about what those worlds are like, and whether they have old or young surfaces.

4. After the discussion below, present students with the Transfer of Knowledge question and ask them to write down their answers.

Reflection & Discussion1. Discuss with students the possibility of an impactor hitting Earth.

Most students are interested in the dangers of this, and you can use the Science Overview for details.

2. Discuss why the students have done this activity in terms of “rela-tive age” instead of absolute age. We cannot know the absolute age of these occurrences or surfaces, unless we go on the locations and test them with experiments that can determine the ages of rocks. If we stay on Earth and look at these surfaces from a distance, relative ages are the only way to measure age.

Transfer of KnowledgeHave students complete the Transfer of Knowledge section in Student Worksheet 2. Here, they are asked to put four surfaces in order by age.


Assessment Criteria for Activity 2

4 Pointsw Student completes Student Worksheet 2 correctly and justifies his or her answers.w Student completes Transfer of Knowledge correctly and justifies his or her answer.

3 Pointsw Student completes Student Worksheet 2 and justifies his or her answers.w Student completes Transfer of Knowledge and justifies his or her answer.

2 Pointsw Student completes some of Student Worksheet 2 and justifies his or her answers.w Student completes Transfer of Knowledge and justifies his or her answer.

1 Pointsw Student completes some of Student Worksheet 2 and justifies his or her answers.w Student completes some of Transfer of Knowledge correctly and justifies his or her answer.

0 Pointsw No work completed.







Lesson Wrap-Up

Resources

Lesson at a Glance

Science Overview

Placing the Activity Within the LessonStudents have now looked at other worlds in the Solar System and the nature of the impact craters on those worlds. Bring the discussion again back to Earth and discuss why there are not very many visible impact craters on Earth. Ask students to hypothesize whether there were impact craters in the past, and whether Earth may change in the future. Ask students, if we were to look for life on other worlds, would we want to look at worlds with many or few impact craters? Why?

Notes on Activity 2:

JOURNEY THROUGH THE UNIVERSE�0

Lesson Wrap-Up

Transfer of Knowledge for the LessonStudents must use the knowledge they have accumulated in Activity 1 about the nature of craters, and the knowledge from Activity 2 about what craters can tell you about the age of objects in the Solar System, and decide the history of the surface in the Transfer of Knowledge Picture found in the back of the lesson.

Lesson ClosureDiscuss with students the Transfer of Knowledge for the Lesson. In Activ-ity 2, students decided whether surfaces were relatively young or old, but in this section, students had to decide the order of processes that occurred on one surface. Discuss how critical this technique could be in deciding what happened to an object in the Solar System long ago, and the history of those objects. For example, whether their surfaces went through a liquid phase a long time ago or a short while ago could help determine the conditions that the entire Solar System (or at least in the part of the Solar System where the object is or was located) was in at those times. Scientists can compare objects in the Solar System as pieces in a puzzle, and begin to put together the big picture of the history of the Solar System. In this way, we have a sequence of events at hand, just waiting for the determination of the absolute age of one or a few events to be able to start to talk in absolute ages rather than relative ages.

Extensions for the Lesson Have students research the current theory of how the Moon was

formed—by a giant impact! Have students research the extinction of the dinosaurs and

how scientists think that it was a massive impact that was the cause of it.

JOURNEY THROUGH THE UNIVERSE �1


Lesson at a Glance

Science Overview





Lesson Wrap-Up

Resources

Assessment Criteria for the Lesson

4 Points Student justified their answer for parts A and B in Transfer of

Knowledge for the Lesson. Student’s answers for Transfer of Knowledge for the Lesson were

both correct.

3 Points Student justified their answer for parts A and B in Transfer of

Knowledge for the Lesson. One of student’s answers for Transfer of Knowledge for the Lesson

was correct.

2 Points Student justified one of their answers for parts A and B in

Transfer of Knowledge for the Lesson. One of student’s answers for Transfer of Knowledge for the Lesson

was correct.

1 Point Student justified one of their answers for parts A and B in

Transfer of Knowledge for the Lesson. Student’s answers for Transfer of Knowledge for the Lesson were

incorrect.

0 Points No work completed.

JOURNEY THROUGH THE UNIVERSE��

Resources

Internet Resources & References

Student-Friendly Web Sites:How Craters Age animation clickworkers.arc.nasa.gov/training/how-craters-age.html Interactive Map of Terrestrial Impact Craters www.lpl.arizona.edu/SIC/impact_cratering/World_Craters_

Web/intromap.html

Teacher-Oriented Web SitesAmerican Association for the Advancement of Science Benchmarks for Science Literacy www.project2061.org/publications/bsl/online/bolintro.htmBarringer Crater Web site www.barringercrater.com/Earth Impact Database www.unb.ca/passc/ImpactDatabase/National Science Education Standards www.nap.edu/html/nses/Terrestrial Impact Craters www.solarviews.com//eng/tercrate.htmVoyage Online www.voyageonline.org/

JOURNEY THROUGH THE UNIVERSE ��


Lesson at a Glance

Science Overview


Resources


Teacher Answer

Key

Teacher Answer Key

Student Worksheet 1

Impact TableStudents’ answers in the impact table will vary. Make sure their mea-surements and calculations were correct based on their materials and their data.

Questions & Conclusions

Questions about the experiment1. There was an area where the marble hit the flour, which became

white because it blasted away the cocoa, leaving the flour exposed. There were lines of white as well coming away from the middle.

2. The cocoa really helps to see how the surface is affected because you can see that more area is affected than just the surface where the marble hit.

3. The bigger the impactor, the bigger the crater (when dropped from the same height).

4. The higher the impactor, the bigger the crater (when using the same size impactor).

5. The energy is really the deciding factor in the size of the crater. No matter what, the higher the energy, the larger the crater.

6. This may or may not be true depending on the size of the impactors the students used. Look at the Impact Table to check the accuracy of their answers.


Questions about craters1. It is fairly accurate, in that it has most of the features from the Lunar

Crater Image, except that it does not have a central peak.

2.

Walls The walls are formed from the material that was not blasted out when the impactor hits the surface (and not from any indentation of the impactor—the walls are much farther out than the original impactor). They show the limit of the material blasted out of the crater.

Floor The floor is formed because the material above it has been blasted up and out.

Rim The rim is formed where the affected material meets the undisturbed material.

Ejecta The ejecta is formed from the material that was blasted out from the crater when the impactor hit.

Rays The ejecta can form rays of material. (Note: In real craters, rays should form when there is no atmosphere, which is not the case in the experi-ment. Be lenient in grading this section because rays may not form and therefore students may not understand how they form.)

Central Peak

The experiment did not form a central peak, but it was probably formed in reaction to the force of the impact.

Transfer of KnowledgeImpactor A hit the Moon with less energy than Impactor B. I can tell this is true because, even though Impact Crater A may look deeper than Impact Crater B (though this may also be just the effect of shadows covering most of the floor of the smaller crater), Crater B is definitely bigger than Crater A. From my experiment, I have found that the more energy an impactor has, the bigger the crater it creates.



Lesson at a Glance

Science Overview


Resources


Teacher Answer Key

Student Worksheet 2These answers are written with the assumption that the students’ only evidence toward their conclusions are the pictures they see. You may decide that students should have a more sophisticated understanding of what is actually going on in the picture if they have past classroom experience. Some leeway should be given to the students answers. If they are basing their answers only on the pictures, a lot of conclusions are possible without knowing anything else about the planet or its moon(s).

1. Mars – There is no evidence of horizontal or vertical motion in any of the photos. There are no folded mountains or places where parts of the surface have moved in relation to other parts. If Mars had volcanoes, they could cover older craters with dust and rocks. We do not see any evidence of volcanoes in these photos, so we can only offer that as a hypothesis. If Mars had an atmosphere, there could be winds that have covered older craters (like the ghost cra-ters) with dust or eroded parts of the crater. If Mars had water at some time, the action of the water would have eroded older craters (like the ghost craters). Since one of the photos shows fresh craters, these must have been formed more recently than those in the other two photos. It appears that dust moved by wind appears likely, maybe some water too (though this is less clear)—for the others, there is not enough evidence to suggest they have been factors.

2. Venus – There seems to be evidence of buckling of the surface in some areas, but these could have been caused by other geologic events besides plate tectonics, too. This action would destroy older craters. There are carters on top of these areas so they must have occurred after the buckling. If Venus had volcanoes, they could cover older craters with lava. Some of the features could be old lava flows. If Venus had an atmosphere, there could be winds that have covered older craters with dust or removed parts of the crater. If Venus had water at some time, the action of the water would have eroded older craters. Some of the features could be old river flows. There are several craters in the buckled area, so they occurred after these areas were formed.

3. Ganymede and Callisto – Callisto appears to have only fresh craters. This would indicate that there is or was no atmosphere and, therefore, no wind. There is no evidence for volcanoes or plate tectonics. There is also no evidence for presence of water in the past or in the present. Ganymede appears to have a buckled surface indicating it could be plate tectonics (but it could also be


caused by something else). This action would destroy older craters. There are craters on top of these areas so they must have occurred after the buckling. There seem to be channels that were cut by lava or water (but we cannot tell which). There are some ghost craters that could have become ghosts as the result of volcanic activity or material that was shot up by other crater hits or by weather.

4. Mercury – No atmosphere or water. There are some ghost craters that could have become ghosts as the result of volcanic activity or material that was shot up by other crater hits or by weather. There is a cut on the surface that goes through some older craters. [The students would not know what caused this. It is believed that this is the result of surface compression.] There is no evidence of plate tectonics.

Transfer of Knowledge1. Two of the most likely orders are: 2,3,4,1 or 2,3,1,4. Photos 2 and

3 show sharp crater rims. This would indicate that the craters in these photos are younger than those in photos 4 and 1. In addition, photo 3 could come before 2, if the object in 2 had some kind of activity in the distant past (but which ceased at some point) that would have obliterated older craters. Therefore, two other orders could be 3,2,4,1 or 3,2,1,4. The order of the last two in each sequence is in question. Both show weathering, but it would be difficult to choose which was older. Again, this would depend on the activity that had occurred on the object in the past.

2. Photo 1 could be Mercury or the Moon because there are many craters ; it looks like the images of the Moon or Mercury shown in this Activity and in Activity 1. This implies that there has been little activity on either body to obliterate craters after their surfaces solidified.

Photo 2 is Mars because it shows fairly fresh craters but not as many as in photo 1.

Photo 3 is Ganymede or Venus because it looks like pictures of their surfaces that were shown previously. Sharp features but no weathering due to wind or water. Photo 4 is Mars because it looks a lot like the NASA/Viking 1 Orbiter photo that was shown previ-ously. They both show either water or lava flows.

3. No. The reasons are explained in the answer to question 1.



Lesson at a Glance

Science Overview


Resources


Teacher Answer Key

4. No. The characteristics (an atmosphere, oceans or other bodies of water, weathering, volcanoes, and plate tectonics) noted at the beginning of Activity 2 play a large part in determining the age of the surface, but the planet may be much older than its surface. The amount of cratering on a world does give an indication of the age of the surface, but only of the surface.

Transfer of Knowledge PicturePart A: Oldest to youngest: B, A, C. The river has eroded away the edge of crater B, and you can see the river flowing through it, so it must have gotten there before the river did. But crater C is not eroded away and appears to be on top of the old riverbed, so it must have gotten there after the river had dried up.

Part B: Answers will vary. The basic idea is that Mars went through a history of cratering, with large craters first. Then river beds formed, perhaps Mars warmed up and allowed rivers to flow on the surface. After the river beds dried up, Mars continued to be hit and craters were created.

Warm-up & Pre-Assessment

Picture of Moon and EarthImages from photojournal.jpl.nasa.gov

page 1 of 1

Student Worksheet 1Creating Craters

Name ______________________________________________ Date ___________

Student Materials (Per pair of students)w 1 pie panw Two pebbles or marbles of different sizesw Scale w Bag of flour or box of cornstarchw Sifterw Metric rulerw Newspaperw Powdered cocoa w Meter stickw Calculator (optional)

Directions1. Use the scale to measure the mass of your two impactors (pebble or marble) and record the data in the

Impact Table on the next page.

2. Cover your area of the floor with newspaper.

3. Fill a pie pan with a thick layer of flour. Smooth out the flour so that it is as flat as possible.

4. Cover the top of the flour with a light dusting of cocoa. Use a sifter if you have one available.

5. Place the pie pan on the floor or on the ground.

6. Place one end of the meter stick on the floor next to the pan and measure 30 cm above the pan.

7. Drop one of your impactors into the pan from the 30 cm height.

8. Remove the impactor, and repeat steps 5 and 6 with a different size impactor, creating a second impact site in the pan so that it is not too close to the first impact. Remove the impactor, and draw a picture in the Impact Table on the following page.

9. Measure the size of your impact craters and record their diameters in the Impact Table.

10. Smooth the flour, sift on a now layer of cocoa, and repeat steps 5-7 for impacts from heights of 20 cm and 10 cm. Calculate the amount of energy for each impact.

page 1 of 6

Impact Table

HeightImpactor Mass Mass 1 _______ Mass 2 _______

Energy * (E = mgh)

Size of crater Draw a picture

30 cm(0.3 m)

30 cm (0.3 m)

20 cm (0.2 m)

20 cm (0.2 m)

10 cm (0.1 m)

10 cm (0.1 m)

* You need to calculate the amount of energy in the impactor when it is dropped toward the pie pan. The amount of energy (E) is equal to the impactor mass (m) times the gravitational constant (g) times the height at which you dropped the impactor (h). This energy corresponds to how much energy the impactor has at the time of impact, so it is a good way to characterize how strong each impact is.

Energy (measured in joules) = mass (measured in kilograms) x gravitational constant x height (measured in meters)

Gravitational constant g = 9.8 m / s2 page 2 of 6

Questions & Conclusions

Questions about the experiment1. How did the appearance of the surface of the flour change after it had been hit by the impactor?

2. What does the cocoa reveal about how impacts change the surface?

3. How does the size of the impactor affect the crater?

4. How does the height from which the impactor is released affect the crater?

5. How does the overall energy of the impactor affect the crater?

6. Are there any cases where a big impactor created a smaller crater than a small impactor, depending on where they were dropped from?

page 3 of 6

Ask your teacher for the Lunar Crater Image and use it to help you answer the questions below.

Questions using Lunar Crater Image1. Compared to the Lunar Crater Image, was your model an accurate representation of lunar craters? Explain why or why

not.

2. Look at the Lunar Crater Image. Examine each part of the image that is listed, and write a description about how each feature occurs, based on your findings from this activity.

Walls

Floor

Rim

Ejecta

Rays

Central Peak

page 4 of 6

Transfer of KnowledgeLet’s assume that a long, long time ago, Impactor A hit the Moon and created Impact Crater A. Around the same time, Impactor B hit the Moon and created Impact Crater B. Now, scientists want to know something about the impactors that created these craters, but the only thing they have to go on is what the impactors left behind—their craters. Look at the picture below of Impact Craters A and B. Based on the impact craters, compare the differences between the two impactors (A and B) that created these craters.

Impactor A hit the Moon with (more, less, the same amount of) energy than Impactor B had when it hit the Moon. I can tell this is true because:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

page 5 of 6

AB

Lunar Crater Image

walls

floor

rim

ejecta

rays

central peak

Figure 1.(Image credit: Part of Apollo 17 Metric photograph AS17-

2923.)Crater Parts

WallsThe sides of the crater bowl. Walls can be very deep, depending on the severity of the impact. They may look like steps, or walls can be shallow. If a crater has shallow walls, then the crater may have been filled or eroded somehow since its formation.

FloorThe bottom part of the impact site. It may be the shape of a bowl, or it may be flat. This part is lower than the surrounding surface.

RimThe edge of the crater; the rim is usually the highest part of the crater.

EjectaThe debris that shoots, or ejects, out of the impact site when the crater forms. There is a lot of ejecta close to the crater, so the layer of ejecta is thick there. The ejecta gets thinner the farther away it is from the crater. The impact creates debris as the shock wave crushes, heats, and melts the rock.

Rays The bright streaks that start at the rim of the crater and extend outward. Rays are created by fine ejecta coming from the crater and are only found on worlds where there is no significant atmosphere (e.g., on the Moon but not on Earth.)

Central Peak A small mountain that may form at the center of the crater in reaction to the force of the impact. Only large craters can have a central peak. The size at which cra-ters can have central peaks depends on the size of the world. For example, on the Earth, craters larger than 2-4 km (1.2-2.5 miles) can have central peaks, while on the Moon, the crater must be larger than 15-20 km (9-12 miles) in diameter.

page 6 of 6

Student Worksheet 2: The Older You Are...

Name ______________________________________________ Date ___________

If a surface is young, it may be because the world may have...

an atmosphere oceans, rivers, or other bodies of water weathering (wind, rain, etc.) volcanoes plate tectonics

1. Look at the three pictures below of the Martian surface. These pictures show how one planet can have parts that are older than others. (Image credits: NASA/JPL/Malin Space Science Systems)

page 1 of 5

Figure 1. This picture shows fairly fresh craters on Mars. Fresh cra-ters usually have a sharp rim, an ejecta blanket, and central peaks. Notice that this part of Mars has many impact craters.

Figure 2. This picture shows degraded cra-ters on Mars that have no ejecta blanket, the rim is eroded, and interior features are gone.

Figure 3. This picture shows ghost cra-ters on Mars that are faintly visible and have been eroded away almost completely. Ghost craters are those that one can still barely see when looking at the surface of an object, and that have probably been there for a long time, getting more and more faded away. Notice that this part of Mars also does not have many impact craters.

Fresh craters usually have a sharp rim, an ejecta blanket, and central peaks (if they were created). Degraded craters usually have no ejecta blanket, the rim is eroded, and interior features are gone.

2. Look at the picture below of Venus. Venus has mostly large craters, but numbers vary across the surface. Venus has a number of fresh, degraded, and ghost craters, but also surfaces with no craters whatsoever.

From this picture and the description of Venus’s craters above, what can you conclude about the characteristics of Venus that may result in these kinds of craters? Pick three characteristics from above and explain your answer

page 2 of 5

Figure 4. Venus. Image credit: NASA

3. Look at the picture below of two moons of Jupiter, Ganymede and Callisto. These Moons have many craters of all kinds (fresh, degraded, and ghost) and sizes.

page 3 of 5

Figure 5. GanymedeImage credit: NASA/JPL

Figure 6. CallistoImage credit: NASA/JPL

From these pictures and the description of Ganymede’s and Callisto’s craters above, what can you conclude about the characteristics of these moons that may result in these kinds of craters? Pick three characteristics from above and explain your answer.

4. Look at the picture at the right of Mercury. This planet has many craters covering its whole sur-face, and they are mostly fresh, although there appears to be some ghost craters.

From this picture and the description of Merucy’s craters above, what can you conclude about the characteristics of this planet that may result in these kinds of craters? Pick three characteristics from above and explain your answer.

Figure 7. Mercury. Image credit: NASA/JPL/Northwestern University

Transfer of Knowledge

1. Put the following cratered surfaces (numbered 1 through 4) in order from youngest to oldest.

2. What objects in Activity 1 or 2 might these be images of?

3. Can you be sure of the order you picked?

4. Does an older surface mean that the planet is older than other planets? Why or why not?

Image credit: NASA/JPL/Northwestern UniversityImage credit: NASA

Image credit: NASA/JPL

Image credit: NASA

1 2

3

4

page 4 of 5

Image credit: NASA

Transfer of Knowledge Picture

The picture below is one of craters and river beds. Use it to answer the following questions.

Image credit: NASA/Viking 1 Orbiter

Part A. Put these objects (A, B, and C) in order of age, and explain why you believe this is the case. Be sure to look at the crater rims to tell you if there has been any erosion.

Part B. Based on the picture above, write a description of the environment around Mars through time. Explain your answer.

A

B

C

page 5 of 5

voyage: a journey through our solar system grades 5-8 ... · pdf filejourney through the...

Documents