Mapping the Surface of a Planet

Objective – Using data sheets, I can identify surface features on Mars.

Mapping the Surface of a Planet

Identifying Surface Features

(source: NASA Mapping the Surface of a Planet)

NASA has been returningimages of Mars since 1965. The Mariner 4 spacecraft flewpast Mars and sent back twenty-one images. Science and technology haveimprovedgreatly over the last 50 years. The Mars Global Surveyorspacecraft has sent back over 100,000 images of the Martian surface. Theseimages have helped scientists determine what geological activityhas occurred to make the planet appear as it does today. Impact craters,volcanoes, layering, and riverbeds look much the same on Mars as they do onEarth. Scientists can, use Earth's features as a comparison forMars. Geological features on Mars are easy toidentify if you know what you are looking for.

Impact Craters

Impact craterson Mars, the Moon,or any other planetary body areformed when meteorites slam intoits surface, creating a crater. Impact craters on Mars varyin size from less than 1 km (0.6miles) to 2,100 km (1,300 miles) indiameter. An impact crater usuallyhas five parts, although not all ofthese parts are visible in all craters.The image at right is of a crater in aregion called Arabia Terra on Mars.It is typical of craters found in our Solar System.

• Rim – This is the raised area around theedge of the crater.It is made of material thrownupward by the impactthat created the crater.
• Ejecta – Material which landedoutside the crater in a blanket. One type of ejecta is long,outward-pointing streaks calledrays.
• Walls – The wallsofthe crater slope down to the floor.
• Floor – The floor is often flat.
• Central Uplift – Ifthe impact was violent enough tomelt the rock which became thefloor of the crater, a central upliftor peak will often form.

Volcanoes

Volcanoesare hills or mountains made frombuilt-up layers of lava(hot, moltenrock) ejected from cracks or ventsin the planet's crust. At the top ofthe volcano is a roughly circulardepression. This depression is calleda calderaif it is larger than one mile(0.6 km) in diameter; a craterif it is smaller thanone mile (0.6 km) in diameter.There are five types ofvolcanoes.

• Shield volcanoesaredomes wider than they arehigh. They also havevery low slopes. They are formedfrom hot, freely-flowing lava.

Earth Mars

• Plug Dome – This type ofvolcano is usually small, rising notmore than a few thousand metersabove the surface. If the lava from a volcano flows slowly, it piles up in the vent.This creates a “plug.”

• Spatter Cones–This type of volcano is similar size to a plug dome.It is formedfrom gas-charged lava fountains thatthrow lava high into the air.

• CinderCone– This type of volcano is formed from volcanic ashand coarse materials exploding fromthe vent.

Earth Mars

• Composite Volcano – This type ofvolcano is actually a blend of theother types, sometimes having quieteruptions and sometimes havingviolent explosive eruptions. MountSt. Helens, which last erupted onMay 18, 1980, is an example of thistype of volcano.

Stratification

The Earth's crust has experiencedmany changes over its 4.5 billion-year history. The crust ismade up of many layers of rock, onelaid on top.This process is called stratification.These rock layers, or strata, tell usmuch about the history of the Earthand how it has changed.The strata form a geological timelinewe can use to date changes in the Earth's crust.Where this timeline is exposed,we can read the history ofthat area. One placewhere we can see strata is in theGrand Canyon. It wasformed over many millions of years. The Colorado River slowly worethrough the surface rock and carveddeep channels. As theriver dug deeper, more layers of rock were exposed.It revealed much about thegeological history of this region.

Canyons also exist on Mars. Some may have been cut by water or lava. The largest canyonon Mars is Valles Marineris, whichis over 10 km (6 miles) deep and4,000 km (2,500 miles) long.

Ifplaced on the Earth, it would stretchacross the entire United States! The strata revealedtell us the story of the planet'shistory. Using cameras aboardspacecraft orbiting Mars, scientistshave found evidence of layeredterrain.

River Beds

Earth Mars

Rivers on Earth form when runningwater carves channels into the land. On Mars, no liquidwater can exist today, so no watercan flow to carve channels. NASAspacecraft instruments, however,have found many examples of long,snake-like formations. These resembledry riverbeds similar to those foundon Earth. At the eastern end ofValles Marineris is a complex systemof outflow channels that drain intothe plain called Chryse Planitia.

These channels were thought tohave formed when water suddenly floodedthe surface.The channels were carved injust a few weeks. It was as if all ofthe water in the Great Lakes weresuddenly drained into the Gulf ofMexico in just two weeks.

There aremany features on Mars, such asNanedi Vallis, shown below, thatindicate that at one time the planetmay have been much warmer andwetter than it is today.

Where didall the water go? Water on Marstoday can exist only as ice or aswater vapor. Scientists believemuch of Mars' water is locked up asground ice deep beneath thesurface. This layer of frozen ice androck, called permafrost, may beseveral kilometers thick. Even afterthe water on Mars froze,large impacts may have melted thepermafrost and temporarily allowedwater to flow.

Water wouldeventually either refreeze or turn tovapor and escape into theatmosphere. The water in theMartian atmosphere is visible todayas wispy ice clouds. If Mars was warmerand wetter in the distant past than itis today, what causedthis change? Could the samechange happen to Earth? These arequestions that scientists areattempting to answer by using datareturned by spacecraft sent to Mars.

Determining the Surface History

Think of the most beautiful and interesting place you have ever seen. Arethere mountains, lakes, volcanoes, rivers, or rocks there? Do you have anyidea how these geological features were formed? Decidinghow the features formed isthe job of geologists.

With what we know about the Earth'ssurface, geologists can determine what is happening on other planets. Onceyou can identify geological features thenext question you should ask is: How were these features formed? Whichfeatures were formed first and are therefore older? Which features wereformed later and therefore are younger?

By asking these questions, geologists can determine the surface history of a planet. Tomake this determination, geologists use three basic rules, or principles. You must learn theseprinciples so that you can determine the history of the areas of Mars you willstudy.

#1 – The Principle of Superposition

This principledescribes the order in which rocksare placed above one another. Youknow from our discussion ofstratification that rocks in the Earth'scrust are laid down in layers, one ontop of the other. The Principle ofSuperposition states that stratalocated at the bottom of a stack of rocks are olderthan the layers at the top of thestack. If you think about it, thismakes sense. Theonly place younger rocks could belaid down is on top of the olderlayers.

The image shows anexcellent example of strata. Whichlayers in this image are the oldest?Which are the youngest? On Earth,geologists canestimate when the rock layers werelaid down. In this way, we discover atimeline of Earth's geological historyin the exposed layers ofrock.

#2 – The Principle of Cross-Cutting Relationships

Thisprinciple states rocks orgeological features such as canyons,rivers, or cracks in rocks, may be cutby other rocks or by other geologicalfeatures. The Grand Canyon was cut as the Colorado River slowly wore its way downthrough the layers of rock toproduce the canyon wesee today. The rocks werecut by the river; they must be olderthan the river. The canyon itself, the“cut” in the rocks, was created bythe river carving its way through therocks. The rocks are theoldest feature, followed by the river,and then the canyon “cut.” Theserelationships help geologistsdetermine the age of differentgeological features on the surface.This process will reveal a lot aboutthe surface history of a region!

#3 – The Principle of Horizontal Bedding

This principle states that rocks that are deposited by water, such as limestone, or rocks that are deposited by wind, such as sandstone, are deposited in nearly horizontal layers. If layers are no longer horizontal, they must have been bent or folded after they were originally laid down.

California lies upon a fault, a moving breakbetween two plates of the Earth's crust. These continental platesare moving very slowly. Over millions of years, the rock layers begin tobend

Now is your group’s chance to apply what you've learned to actual images of the Martian surface.

The goal of this activity, and the ones that follow, is to give you practice analyzing actual data sets from Mars in order to determine the surface history of the planet. You will need to be able to recognize the various geological features and apply the three principles we studied to determine the ages of those features. Once you have the ages of all the features, you will develop hypotheses of how those features were formed.

The image included with this activity was taken by the Mars Orbiter Camera (MOC), one of the three instruments aboard the Mars Global Surveyor (MGS)spacecraft.

Names ______

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Mapping the Surface of a Planet

Activity One

Features Near Olympus Mons (MOC2-102)

1. The image has been overlaid with a grid that has been marked inkilometers so that you can record the positions of features you identify.

a) What is the width of the area shown on the image? ______km

b) What is the length of the area shown on the image? ______km

2. Examine the long, winding feature that extends from the bottom left to thetop right of the image. Is it raised above the surface or is it carved into thesurface? What is your hypothesis?

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3. In order to answer question 2, you actually need more information.

4. TheSun is illuminating the picture from the right. Look at the circular feature just

above and to the right of the center of the image. If the Sun is shining from

the right side of this feature, is it a volcano or an impact crater?

______

5. For this image, if the shadow is on the right side of a feature, is that feature

raised or lowered? ______If the shadow is on the left side, is that

feature raised or lowered? ______

6. Olympus Mons, the largest volcano in the Solar System, produced the lava

flows that you see in the upper left corner of the image. Which feature is

older, the lava flows or the long winding feature that extends across the

image?______

• TheSun is illuminating the image from the right.

• Look at the crater in the 4-5 km, 4-5 km block. If the Sun is shining fromthe right side of this feature, is it a volcano or an impact crater?

______

For this image, if the shadow is on the right side of a feature, is that featureraised or lowered? ______If the shadow is on the left side, is thatfeature raised or lowered? ______

7. Olympus Mons, the largest volcano in the Solar System, produced the lavaflows that you see in the upper left corner of the image. Which feature isolder, the lava flows or the long winding feature that extends across theimage?

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8. Complete the Data Log below, identifying as many features (such ascraters, canyons, riverbeds, and volcanoes) in the image as you canrecognize. Record the grid coordinates of each feature on the Log so that youcan find them later. After you have identified these features, use the threeprinciples you learned previously to rank the features from oldest toyoungest. Be sure to explain your reasoning in the “Notes”section! Finally,in the space below “tell the story” of what has happened to form the featuresshown in this image in your own words.

Features Near Olympus Mons (MOC2-102) Data Log

Features / Grid Coordinates / Age Rank / Height
Features / Grid Coordinates / Age Rank / Height

Notes

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Activity Two

The second instrument aboard the Mars Global Surveyor spacecraft is theThermal Emission Spectrometer (TES). The purpose of TES is to measurethermal infrared (IR) energy that is emitted from Mars. We often perceivethermal IR energy as heat. Just like visible light, thermal IR energy exists inmany different “colors” or wave-lengths. These “colors” however, are so redthat your eye can't perceive them. TES has a special instrument which cannot only see these wavelengths, but it can also measure how much of eachwavelength is present. The instrument is also capable of measuring the totalamount of energy reflected from the surface of Mars. Material with a highalbedois shiny and bright because it reflects a great deal of light, whilematerial with a low albedo does not reflect much light and appears dark. Youwill use TES's measurement of the albedo of the Tharsis Province to learnmore about the unique geology of this region.

Albedo of the Tharsis Province

1. Examine the scale printed below the TES image. This scale shows thepercentage of visible and IR light received from the Sun that is beingreflected from the surface of Mars.

a) What is the minimum percentage of visible and IR light that isreflected in the

image? ______

b) If you were looking at this area through a telescope, would itappear light or

dark? ______

c) What is the maximum percentage of visible and IR light that isreflected in the

image? ______

d) If you were looking at this area through a telescope, would itappear light or

dark? ______

e) Approximately what percentage is represented by a dark greencolor?

______

2. Find the three volcanoes of the Tharsis Montes region. The volcanolocated on the lower left is called Arsia Mons, the volcano in the middle isPavonis Mons, and the volcano located to the upper right is Ascraeus Mons.

a) Which of these volcanoes has the highest albedo? ______

b) Which of these volcanoes has the lowest albedo? ______

3. The large volcano northwest of (to the left and above) the Tharsis Montesis Olympus Mons, the largest volcano in the Solar System. Notice that thereis a region of very bright material on the northwest face of the volcano. Thisbright material is actually not on the surface, it is water-ice clouds in theatmosphere.

a) Which side of Olympus Mons is the material on? ______

b) Now look at the Tharsis Montes. Which side is the material on here?

______

c) Why do you think the material is only found on one side of thevolcanoes?

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d) What does this tell you about the winds on Mars?

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4. Look at the filmy white feature stretching northeast from Pavonis Monsand lying southeast of Ascraeus Mons. This feature is Valles Marineris, thelargest canyon in the Solar System. The canyon is marked by material that issimilar in albedo to the material on the northwest side of the Tharsis Montes.

a) What do you think this material might be? ______

b) Why do think this material would collect in the canyon?

______

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5. Look at the red-colored region near the north pole of Mars (the blackcircular area here is just the area where Mars Global Surveyor could notcollect data).

a) Is this region bright or dark? ______

b) Why do you think the region appears this way (bright or dark)?

______

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Activity Three

The third major instrument on board the Mars Global Surveyor spacecraft isthe Mars Orbiter Laser Altimeter (MOLA). This instrument, controlledfrom NASA's Goddard Space Flight Center in Greenbelt, Maryland, transmitsinfrared laser pulses towards Mars. These pulses bounce off the Martiansurface and the instrument measures the time it takes to receive the returnpulse. Because light (and an infrared laser pulse) always travels at the samespeed, the instrument can measure the distance from the spacecraft to thesurface with a great deal of accuracy. The image you will use in this activityshows the topographyor heights, of the region surrounding the threeTharsis Montes volcanoes. This image is not a photograph! A computergenerated this image by assigning colors to represent different heights aboveor below the datum, or “sea level” on Mars. The color scale below the imagewill allow you to determine the heights of the features.

Topography of the Tharsis Montes Region

1. The grid on this image is marked in degrees of latitude and longitude. TheMartian equator runs directly through the middle of the image at 0 degreeslatitude. One degree of latitude or longitude in this region is about 59 km.

a) What is the width (in degrees) of the image? ______o

b) What is the length (in degrees) of the image? ______o

2. Notice the three volcanoes that cross the image from bottom left to topright.

a) How tall (in meters) are these features above the datum?