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With this hands-on activity, students will learn the basic concepts of planetary geologic mapping based on photointerpretation of spacecraft images of planetary surfaces. They will practice on different images of planet Mars, reconstructing the sequence of events that shaped that precise place of the red planet, learning to become real Geo-detectives!
Scientistis study other planets and moons using images caught by cameras onboard space missions. But, not being able to land and observe these surfaces directly, they do not have direct information on the material of surface rocks and historic data on surface events. So they need landers to examine rocks dirctly and they need to reconstruct surface geology from morphology, the shapes (relief) and patterns of the terrain.
Scientists so learn how to distinguish between observations and interpretations. For observations, we use a descriptive vocabulary. For interpretations, they reconstruct the evolution history of that surface, deducing the geologic processes that must have happended on the surface.
To do this, it is important to recognize the morphology, the shapes ofwhat we see on these surfaces. Some of these shapes are due to geological phenomena that we know very well on Earth.
There are geological features that we can identify and study on Earth that can also be found on other terrestrial (or rocky) planets and moons.
Let’s start with some definitions:
Image: Young impact craters. Left: Meteor (Barringer) Crater in Arizona, USA. The crater is about 1 km across and is 50,000 years old. Perspective view. Credit: Shane.torgerson, Wikimedia Creative Commons Attribution 3.0 Unported https://creativecommons.org/licenses/by/3.0/deed.enRight: A young impact crater on Mars. The crater is about 1 km across. The upper part of the image is in color. HiRISE ESP_012857_1910 NASA/JPL-Caltech/UArizona
Image: young and old simple craters on the Moon.
Image: caldera. Left: Aerial photo of Halemaumau pit crater in 2009, showing a white plume being emitted by a small, active lava lake. The crater is located within the much larger Kīlauea caldera of Hawaii. Credit: Hawaii Volcano Observatory, USGS Right: The nested, complex caldera at the top of the highest volcano on Mars, Olympus Mons. The caldera is 10 km across. Credit: ESA/DLR/FU Berlin (G. Neukum)
Image: Lava flow. Left: Lava flow from Sabancaya Volcano, Peru. Credit: NASA, International Space Station Science, 07/15/10, Attribution-NonCommercial (CC BY-NC 2.0) Right: Lava flow on Mars, from the south slope of Arsia Mons at 20.824°, 233.290°E. THEMIS image, Credit: NASA/JPL-Caltech/Arizona State University.
Image: Channel and streamlined island: Left: Small channels with streamlined islands, on the sandy beach of Galveston, Texas. Credit: HH (author). Right: Channels on Mars, east of Olympus Mons, flanked by lava flows. The channels contain additional lava flows but water may have also flowed in it in the past. It is probably a lava channel. It has streamlined and more irregular islands, created by water or very fuid (low-viscosity) lava. Credit: NASA/JPL-Caltech/Arizona State University.
To learn how to get information by observing images from satellites, watch the following introduction video on how to become a Geo-detective! This video can also be used in calssroom to be shown to the students (see Activity 0).
Link to the video
Distinguish between negative and positive reliefs
The first thing to know when approaching an image of a planetary surface is how to distinguish between negative and positive relief using light and shadows to distinguish high and low relief forms from flat surfaces (see the video to better understand how).
Image: This figure explains the relationship between the direction of illumination, shadows /shading and relief. The same image can result from two different relief situation depending on where the illumination comes from. Without familiar objects, or knowing the direction of the Sun, we are unable to determine the correct relief. The left hand part of the figure shows relief from the ground as a cross section while the right hand side shows the same objects from above as seen on a spacecraft image. The upper part shows how depressions would look like, and the lower part shows elevations.
Distinguish old from new surfaces
Geologists reconstruct the story of how a landscape formed by determining which rocks and forms formed when in that region.
In stratigraphy, you will have four tools to determine which unit is older. Results from the four tools should be consistent with each other.
Image: an image of the Moon where you can see the importance in crater density to evaluate the age of a surface. The smooth, dark mare (lava plain) is younger (left side – it has only few, small craters). The rough, densely cratered highland terrains are older (right side). The rough surface is the result of crater depressions and crater ejecta on the top of each other. Credits: NASA.
For this Introduction activity you will need to project the slides or distribute printed copies of Introduction.ppt and stimulate a class discussion with students, asking questions and discussing answers.
Image 1: Mars. Part of Marte Vallis, Mars. It is a south from the large volcanic Elysium Rise. Credits NASA/JPL/MSSS
see Video at Link https://drive.google.com/file/d/1FMbxK-p1sTakHe0gd1PXT4n2EDgqmZ8s/view?usp=sharing
Image 2: Mars map with outlines. Credits: Henrik Hargitai
NOTE: Why is the outline of the crater in the image above larger than you would imagine? Be careful, because the bowl-shaped depression is only part of a crater! The outline should be at the base of the rim, including the rim and the depression. This is the outline of the crater's geomorphologic unit. In the outline the rocky materials thrown out from the crater can be included too. This is the crater's geologic unit, because it includes every material on the ground that is connected to the formation of this crater. The material of the ejecta in older craters is already eroded away. So be careful! In our exercises when we do geologic mapping, we should map the material (rock) units that formed in one event, and not the geomorphic shapes of the landscape.
Image 3: Mars map with outlines and colored zones. Credits: Henrik Hargitai
Image 4: Mars map with history. Credits: Henrik Hargitai
In Handout and Handout with solutions, we provide Images to be used to replicate the activity on other geological areas.
Four different images from Mars are provided to be used in this activity. One of them can be used as a final evaluation to understand how much students have learned from this activity.
On this map the teachers can ask students to: