Stories of Other Worlds
Dating Surface Ages with Craters---Thought Puzzles
Earth Science Essentials
by Russ Colson
Make sure you've read and understood the text before starting this exercise, especially as it deals with measuring the surface age of planets by crater density.
Thought Puzzle 1--Two Surfaces on One Planet:
Consider the illustration below of a planet's surface, with two surface areas, A and B, designated. Presuming an average cratering rate of 1 crater per 2,000,000 years in each of regions A and B, and presuming this rate is constant (not realistic of course) answer the following questions:
Thought Puzzle 2--Age of volcanos on Mars
Olympus Mons is the largest volcano on Mars. This shield volcano, similar to volcanoes in Hawaii,measures 624 km (374 mi) in diameter by 25 km (16 mi) high. It is 100 times larger than Mauna Loa on Earth. Located on the Tharsis Plateau near the equator, Olympus Mons is bordered by an escarpment. The caldera in the center is 80 km (50 mi) wide and contains multiple circular, overlapping collapse craters created by different volcanic events. The radial features on the slopes of the volcano were formed by overflowing lava and debris.
The surface area within the escarpment circling the volcano is about 337,000 square kilometers.
Count the number of impact craters within this same area to determine the crater density and estimate the age of this volcano.
Take note that the sun is coming from the left in the picture below--this allows you to tell the difference between a hill and a crater. Also, the circular features at the very top of the volcano are calderas, not impact craters--so don't count them.
To use the graph below the picture, you will need to know the size of the impact craters that you can see (there might be many more craters too small to see in this image). Big craters are much more rare than small craters, so you need to take the crater size into account when you estimate age. You can calculate the crater size by using the approximate scale provided.
Thought Puzzle 3--Age of Maré on the Moon
As we determined in a previous lesson, molten basaltic lava cut this channel, known as Hadley Rille, through the surface of the Moon. The channel winds along the base of the Apennine Front, one of the sites explored by the Apollo 15 astronauts. The walls of the channel are very steep, with slope angles of 25 to 30 degrees. The Maré Imbrium, across which Hadley Rille winds, is one of the 'younger' terrains on the Moon.
Last updated Oct 15, 2015. All text and pictures are the property of Russ Colson. Pictures from Mars and Moon courtesy of NASA. Crater density vs time graphs modified from Hartmann, Moons and Planets, 1993.
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