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Geology - Our Solar System

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    Study Guide Geology – Our Solar System 1. Earth’s Moon Scientists have learned a lot about Earth’s Moon through many years of study. They have used powerful telescopes and information from both uncrewed spacecraft and crewed missions. Each of these methods has helped us better understand what the Moon is like on the surface and deep inside. 1.1 Studying the Moon’s Interior When astronauts visited the Moon, they left behind special instruments called seismic detectors . These tools measure vibrations inside the Moon. Today, they record about 400 small moonquakes every year . Most scientists believe these moonquakes happen because of Earth’s gravity . As Earth pulls on the Moon, it causes tiny movements along cracks, or faults, in the Moon’s crust. 1.2 Layers Inside the Moon Seismic data show that the Moon has a layered interior , much like Earth. • The outer crust is about 65 kilometers thick . • This crust is made mainly of basalt and feldspar - rich rock . • Beneath the crust, scientists believe there is a mantle , even though it cannot be directly observed.

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    Study Guide Calculations also show that the Moon is solid down to about 1,000 kilometers . This depth marks the lower boundary of the Moon’s lithosphere , which includes the crust and the rigid upper part of the mantle. 1.3 Features on the Moon’s Surface The Moon’s surface shows clear differences between regions: • The large, smooth lowlands are covered by basaltic lava flows , formed when molten rock once spread across the surface. • The mountainous regions are higher and rougher. Geophysical measurements suggest that these mountainous areas are isostatically balanced . This means that long ago, the Moon’s lithosphere was soft enough to allow thicker crustal regions to “float,” much like ice floating on water. 1.4 Moon Rocks and Their Age Astronauts also brought back rock samples from the Moon. These rocks include: • Anorthosite , a feldspar - rich igneous rock commonly found in the Moon’s crust • Basalt , which formed from cooled lava flows Scientists have dated these rocks and found that they are between 3.0 and 4.5 billion years old . The oldest of these rocks likely formed around the beginning of the solar system . 2. Mars 2.1 Mars and Earth: What’s Similar and What’s Di ff erent Mars shares several features with Earth, which is why it fascinates scientists. A day on Mars lasts almost 24 hours, very close to an Earth day. Mars also has an atmosphere, polar ice caps made mainly of carbon dioxide, and experiences seasons like winter and summer. However, there are important differences too. Unlike Earth, Mars does not have a strong, dipolar magnetic field. This means it is less protected from solar radiation. So far, scientists have not found any direct evidence of life on Mars, although research is still ongoing.

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    Study Guide 2.2 Volcanoes and Landscapes of the Northern Hemisphere The northern hemisphere of Mars is famous for its massive volcanoes. This region contains large shield volcanoes and many volcanic cones, with impact craters spread far apart. Some of these volcanoes are enormous — up to three times taller than the tallest volcanic mountains on Earth. The most impressive of all is Olympus Mons , the largest volcanic structure ever discovered in the solar system. The huge size of these volcanoes tells scientists two important things: • Magma must have flowed to the surface for a very long time. • The Martian lithosphere (the rigid outer layer of the planet) is extremely strong. Scientists have also identified horst and graben fault basins, which form when the planet’s crust stretches and breaks. Many volcanic cones show very little damage from meteor impacts. This suggests the volcanic activity is relatively recent. In fact, the newest lava flows may be less than 100 million years old , based on the low number of craters on their surfaces. 2.3 The Cratered Southern Hemisphere The southern hemisphere looks very different. Instead of volcanoes, it is covered with thousands of impact craters. This heavy cratering shows that the surface is much older and that volcanic activity there has been far less intense compared to the north. 2.4 Surface Materials, Wind, and Signs of Water The Martian surface is heavily weathered and made mostly of clay and sulfate materials. Strong winds shape this loose material into large sand dunes, which are common across the planet. Mars also shows features that look like winding, braided channels. These resemble river systems on Earth and suggest that running water — or even massive floods — once shaped the surface. Scientists think flooding could have happened if: • Frozen ground suddenly melted due to volcanic (magmatic) heat, or • A major change in climate caused ice to thaw quickly.

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