Mapping Surface of a Planet (1)

LAB: Mapping the Surface of a Planet Written and Developed by: Keith Watt, M.A., M.S. Assistant Director ASU Mars Education Program Edited by: Paige Valderrama, M.A. Assistant Director ASU Mars Education Program Sheri Klug, M.S. Director ASU Mars Education Program (C) 2002 ASU Mars Education Program. All rights re-served. This document may be freely distributed for non- commercial use only.

MAPPING THE SURFACE OF A PLANET Identifying Surface Features The National Aeronautics and Space Administration (NASA) has been returning pictures of Mars back to Earth since 1965, when the Mariner 4 spacecraft flew past Mars and sent back twenty-one images. Science and technology have progressed greatly since the early mission days. The Mars Global Surveyor spacecraft has sent back over 100,000 pictures of the Martian surface. These pictures have helped scientists determine what types of geological activity have 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 on Earth. Scientists can, therefore, use Earth's features as a comparison for Mars. In these activities you are a mission scientist trying to figure out what is happening on the surface of Mars. Geological features on Mars are easy to identify if you know what you are looking for. The following is a description of some of the most common geological features on Mars. Becoming familiar with these features will assist you in completing the activities that follow. Impact Craters Impact craters on Mars, the Moon, or any other planetary body are formed when meteorites slam into its surface displacing rock and soil, creating a bowl-shaped hole or crater.  Impact craters on Mars vary in size from less than 1 km (0.6 miles) to 2,100 km (1,300 miles) in diameter. o The picture on the following page is of a crater in a region called Arabia Terra on Mars. It has a morphology typical of many of the Martian craters.  An impact crater usually has five parts, although not all of these parts are visible in all craters. o The rim : the raised area around the edge of the crater is material that was thrown upward by the violence of the impact that created the crater. o Ejecta: Some of the material that was in the crater was thrown high into the air and landed outside the crater in a blanket called ejecta. o Rays: One type of ejecta is long, outward pointing streaks called rays . These rays are particularly visible on the Moon. o Walls of the crater slope down to the floor , which is often remarkably flat. o The central uplift: If the impact was violent enough to melt the rock which became the floor of the crater, a central uplift or peak will often form, a result of a rebound action (like a water

MAPPING THE SURFACE OF A PLANET Volcanoes On both Earth and Mars, volcanoes are hills or mountains made from built-up layers of lava (hot, molten rock) ejected from cracks or vents in the planet's crust.  There are five major types of volcanoes (see following figures): o Shield volcanoes are domes much wider than they are high (shaped like a shield) and have very s h a l l o w slopes. They are formed from hot, freely flowing lava (usually silica-poor basalt) centered atop magma plumes, or “hot spots,” as well as along divergent tectonic zones.  The largest volcano on Earth is a shield volcano called Mauna Loa , which rises over 9 km (5.4 miles) from the sea floor.  The largest volcano in the Solar System, Olympus Mons, Mars, is a shield-like volcano, rising 27 km (17 miles) high, and measuring 700 km (430 miles) across! o Composite volcanoes, also known as stratovolcanoes . These are the most common volcano type on Earth, associated with subduction zones related to Earth’s plate tectonic activity, and the most violent as they can erupt with a powerful explosive force, the result of trapped gasses escaping the silica-rich viscous magma.  A classic composite volcano is conical with a concave shape that is steeper near the top. Composite cones are large volcanoes (many thousands of feet or meters tall) generally composed of lava flows, pyroclastic deposits, and mudflow (lahar) deposits, as well as lava domes .  Mount St. Helens , which last erupted on May 18, 1980, is an example of this type of volcano. o Volcanic dome (lava dome) : Domes form from the slow extrusion of highly viscous silicic lava, too thick to spread out into a lava flow. Most domes are small, and many do not have a summit crater. Domes can form volcanic edifices in their own right such as Lassen Peak in Lassen Volcanic National Park or extruded in the summit craters of composite volcanoes as part of a post-caldera eruptive phase, such as at Redoubt Volcanoes in Lake Clark National Park .  This type of volcano is usually small, rising not more than a few thousand meters above the surface. o Spatter cones: S patter cones formed as hot lumps of lava were thrown a short distance into the air only to fall back to earth around a small central vent. As the still-molten blobs landed on top of each other, they cooled and adhered to nearby pieces to form the walls of what could be considered a mini-volcano. o Cinder cones are formed from volcanic ash and coarse materials exploding from the vent. The most famous cinder cone appeared in a Mexican farmer's cornfield in 1943, Mt. Paricutin growing to over 400 meters (1300 feet) in nine years.

 At the top of the volcano is a roughly circular depression. This depression is called a caldera if it is larger than one mile (0.6 km) in diameter or, confusingly enough, a crater if it is smaller than one mile (0.6 km) in diameter. Schematic diagram of a composite volcano (left). (Credit: Modified from USGS illustration). Eruption of Mt. St. Helens, WA, 1980 (right) Schematic diagram of a shield volcano (top). (Credit: Modified from USGS illustration). Mauna Loa volcano, HI (bottom)

MAPPING THE SURFACE OF A PLANET Stratification The Earth's crust has experienced many changes over its four and a half billion-year history. The crust is made up of many layers of rock, one laid on top of the other in a process called layering or stratification . These rock layers, or strata , tell us much about the history of the Earth and how it has changed over time.  The strata form a geological timeline that we can use to date significant changes in the Earth's crust. Wherever this timeline is exposed, we can easily read off the history of that area. One spectacular place where we can see the strata that make up the Earth's crust is in the Grand Canyon . o The canyon was formed over many millions of years as the Colorado River slowly wore through the surface rock and carved deeper and deeper channels. As the river dug deeper, more layers of rock were exposed, revealing the deep time of this region. Canyons also exist on Mars, such as:  Valles Marineris , the largest canyon on Mars, is 7 km (4.4 miles) deep and 4,000 km (2,500 miles) long. If placed on Earth, it would stretch across the entire United States, many times larger than the Grand Canyon here on Earth. o Valles Marineris was formed not by flowing water or lava, but by massive tectonic forces causing the Martian crust to bulge and pull apart. o Regardless of whether a canyon was formed by flowing water or by a separating crust, the strata revealed tell us the same story of the planet's history. Using cameras aboard spacecraft orbiting Mars, scientists have found evidence of layered terrain. Could these layers tell us how Mars has changed over time? This is one of the questions scientists hope to answer by studying the strata found on Mars. Exposed layers of rock ( strata ) as seen in Grand Canyon, AZ formed by a combination of tectonism and gradation due to flowing water.

Top: Valles Marineris formed by tectonic forces (NASA). Below: Layered terrain (strata), Arabia and East Xanthe Terra region of Mars (NASA).

Mississippi R., Earth, MISR Images, NASA Nanedi Vallis, Mars Mars Global Surveyor, NASA

MAPPING THE SURFACE OF A PLANET Determining the Surface History As geologists piece together the geologic story of a planetary surface, there are three basic principles of interpretation that are followed:  Principle of Superposition  Principle of Cross-cutting Relationships  Principle of Original Horizontality Following these principles, geologists can begin to answer such basic questions as:  How were these features formed?  Which features were formed first and are therefore older?  Which features were formed later and therefore are younger? The Principle of Superposition The Principle of Superposition . This principle describes the order in which rocks are placed above one another.  Simply stated, strata located at the bottom of an undisturbed sequence of rocks are older than succeeding layers above. o The picture below illustrates this principle in an area on Mars revealing exposed strata in horizontal layers. Which layers in this picture are the oldest? Which are the youngest? o By examining the different rocks and fossils (if any exist) within these layers, geologists can interpret the geologic story of a region. preserved in the exposed layers of rock. o In areas where the layering is not exposed, geologists drill into the ground and remove long tubes of rock called core samples. These core samples reveal the layering of rock beds in exactly the same way. Exposed strata at Victoria Crater, Mars Mars Opportunity Rover, NASA

The Principle of Original Horizontality The Principle of Original Horizontality states that rocks deposited by the actions of flowing water, wind, and/or glacial movement, are deposited in nearly horizontal layers (see the Grand Canyon below). If the layers are no longer horizontal, they must have been bent or folded after they were originally deposited. What forces could have caused these layers to fold? o Earth’s lithospheric plates are moving very slowly, and over millions of years, create immense compressional forces, causing rock layers to fold, fracture, and deform . o Even though rock appears to be very hard and undeformable, given enough time, heat, and applied pressures, rocks can flow like putty , behaving in a plastic manner. o Likewise, if the rock unit is subject to hi stress, very suddenly, it can behave in a brittle manner and fracture. o In either case, the rock units must have been deposited as a flat, horizontal structure. Gravity will not allow it any other way. Horizontal layers of rock Grand Canyon, AZ Photo by K. Cole Folded rocks in Agios Pavlos, Greece

MAPPING THE SURFACE OF A PLANET – ACTIVITY 1 Now is your chance to apply what you've learned to actual images of the Martian surface. 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. MGS was launched November 7, 1996, and arrived at the Red Planet on September 12, 1997. The spacecraft completed its primary mission on January 31, 2001, but was still in good health so controllers decided to extend its mission. 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 presented here to determine the relative ages of those features. Once you have the ages of all the features, you will develop a n h ypotheses of how those features were formed. Features Near Olympus Mons (MOC2-102) 1. The image has been overlaid with a grid that has been marked in kilometers 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 the top right of the image. Is it raised above the surface or is it carved into the surface? What is your hypothesis? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 3. In order to answer question 2, you actually need more information: the Sun is illuminating the picture from the right. Now 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? ______________________________ 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 f eature raised or lowered? _________________________. 4. 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? ___________________________________________________________________________ ___________________________________________________________________________

MAPPING THE SURFACE OF A PLANET - ACTIVITY 2 The second instrument aboard the Mars Global Surveyor spacecraft is the Thermal Emission Spectrometer (TES) . The purpose of TES is to measure thermal infrared (IR) energy that is emitted from Mars. We often perceive thermal IR energy as heat. Just like visible light, thermal IR energy exists in many different "colors" or wavelengths . These "colors", however, are so red that your eye can't perceive them. TES has a special instrument which can not only see these wavelengths, but it can also measure how much of each wavelength is present. The instrument is also capable of measuring the total amount of energy reflected from the surface of Mars. Material with a high albedo is shiny and bright because it reflects a great deal of light, while material with a low albedo does not reflect much light and appears dark. You will use TES's measurement of the albedo of the Tharsis Province to learn more about the unique geology of this region. Albedo of the Tharsis Province 1. Examine the scale printed below the TES image. This scale shows the percentage of visible and IR light received from the Sun that is being reflected from the surface of Mars. a. What is the minimum percentage of visible and IR light that is reflected in the image? ________________________________ b. If you were looking at this area through a telescope, would it appear light or dark? _______________________________ c. What is the maximum percentage of visible and IR light that is reflected in the image? _______________________________ d. If you were looking at this area through a telescope, would it appear light or dark? ________________________ _______ e. Approximately what percentage is represented by a dark green color? ____________ 2. Find the three volcanoes of the Tharsis Montes region. The volcano located on the lower left is called Arsia Mons, the volcano in the middle is Pavonis 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? _____________________________