Chapter 9. ASTRONOMY 202 Spring 2007: Solar System Exploration. Class 27: Planetary Geology [3/26/07] Announcements.

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1 ASTRONOMY 202 Spring 2007: Solar System Exploration Instructor: Dr. David Alexander Web-site: Class 27: Planetary Geology [3/26/07] Announcements Planetary Geology Planetary Surfaces Planet Interiors: Terrestrial Planets Chapter 9 Structure of the Interior Internal Heat The Mantle and Lithosphere Planetary Core and Magnetic Fields Now Playing:

2 Announcements Web Project WINDOW CLOSES TODAY Observing TBD Homework Homework #7 is available online and due Mon Apr 2

3 Impact Cratering Impacting objects typically hit a planet s surface at 30,000 to 250,000 km/hr. Craters are generally 10 times wider than the impacting object and about 10-20% as deep as they are wide. Crater is the Greek word for cup.

4 Impact Cratering Number and size distribution of craters on the surface of a planet tell us the age of the planet s surface. Crater shapes reveal the surface history and surface conditions of a planet.

5 Volcanism The term volcanism refers to leakage of molten lava through the planet s lithosphere as well as volcanic eruptions. The molten rock (magma) rises because it is less dense than solid rock and because tectonic forces may squeeze the magma upward under pressure. There are three types of volcanic flow: Low viscosity basalt lavas flow far and flatten out before solidifying creating volcanic plains Moderate viscosity lavas solidify before completely spreading out resulting in shield volcanoes Most viscous lavas build up tall steep stratovolcanoes

6 Volcanism Shield Volcano Volcanic Plains Stratovolcano

7 Volcanism: Outgassing Volcanism provide the means for the formation of planetary atmospheres (and oceans). Virtually all the gas that made the atmospheres of Venus, Earth and Mars (and the water vapour that created Earth s oceans) was originally released from the planet s interior by outgassing. Volcanic outgassing on Io Volcanic outgassing on Mount St. Helens The presence of volcanism on the terrestrial planets can be traced directly to the planet s size since volcanism requires substantial interior heat. Mercury and the Moon cooled more quickly because of their small size.

8 Tectonics Continental Drift or plate tectonics explains the movement of the Earth's plates and also explains the cause of earthquakes, volcanoes, mountain range formation, and many other geologic phenomenon. The plates are moving at a speed that has been estimated at 1 to 10 cm per year. In 1915, the German geologist and meteorologist Alfred Wegener ( ) first proposed the theory of continental drift and hypothesized that there was an original, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth". Pangaea began breaking up during the Jurassic period, forming continents Gondwanaland and Laurasia, separated by the Tethys Sea The carpenter Tekton, son of Harmon, the Adjuster, constructed for Paris the ship which brought Helen to Troy and was particularly beloved of Athena.

9 Tectonics Ongoing tectonics can occur only on planets with mantle convection. Caused by compression and stretching of lithosphere. Multiple fractures on Earth created plates which move under, over and around each other.

10 Erosion

11 Erosion Erosion is a blanket term for a variety of processes that break down or transport rock through the action of ice, liquid or gas. The presence or absence of erosion can be traced to fundamental planetary properties. Erosion can occur only on a planet with a significant and moving atmosphere. Requirements for erosion: Planetary Size: need large planet to sustain and atmosphere Distance from Sun: atmospheric temperature governed by Sun Rotation Rate: drives winds

12 Planetary parameters affecting geology

13 Planetary parameters affecting geology

14 Planetary parameters affecting geology

15 Geology of Venus Geology of Venus mapped out by radar on the Magellan spacecraft Venus is very similar in size to the Earth and are in the same basic region of the solar system. Crater counts suggest that the surface of Venus is about 1 billion yrs old. Shield and Stratovolcanoes Little sign of erosion on Venus Tectonic stress marks

16 Key Geological Trends