Lecture 9 The Geology of the Inner Planets October 5, 2015

Transcription

1 Lecture 9 The Geology of the Inner Planets October 5,

2 2 Clues to the Interior Structure of Planets Mean (Average) Density Mean Density Mass kg 3 Volume Water ~1000 kg/m 3 Rocks ~ kg/m 3 Metals ~ kg/m 3 Compare average density to known densities The mean density of the Earth is 5500 kg/m 3 m

3 3 Clues to the Interior Structure of Planets Many planets act like a magnet Magnetic field caused by a dynamo. To produce a magnetic field you need moving electrical charges, such as liquid metals spinning quickly in the core of a planet.

4 4 The Earth s Magnetosphere

5 5 Magnetosphere traps charged particles emitted from the Sun in region called Van Allen Belts protons and electrons high energies The Van Allen Belts

6 6 Aurora If solar activity is strong, some particles will leak into the atmosphere causing aurora (Northern and Southern Lights)

7 7 Structure of the Earth Average density ~ 5500 kg/m 3 Earth mostly rock and metal Silicon, iron, and oxygen very common. Interior structure of Earth can be determined by looking at how earthquake waves move through the Earth.

8 8 Interior Structure of the Earth Crust: thin, rocky Mantle:basalts Outer core: Liquid iron and nickel magnetic field seismic studies Inner core: Solid iron and nickel

9 9 Plate Tectonics on the Earth Lithosphere = solid crust and upper mantle. Mantle further down is more plastic and can flow. Lithosphere is fractured into many plates floating on denser mantle material

10 11 Geologic Activity on the Earth Most activity occurs near plate boundaries Earthquakes Volcanism

11 12 Earth s magnetic field originates in A. a solid, permanently magnetized core. B. the polar regions of the magnetosphere. 79% C. currents of molten iron deep inside the planet. D. intense electric currents in the Van Allen belts. 11% 6% 4% A. B. C. D.

12 13 Mercury Likely geologically dead Many craters Highlands ~ 3.8 byrs old Intercrater plains ~ older than 3 byrs old NASA's Mariner 10 spacecraft made its first flyby of Mercury in March 1974, and was also the only Mariner mission to visit two planets (the other was Venus). Images beamed back by the spacecraft from 437 miles above the planet revealed a surface very similar to that of the moon. However, Mariner 10 only had enough time to map half of the planet -- which is a big reason why NASA recently sent their MESSENGER spacecraft to Mercury.

13 14 Interior Structure of Mercury = 5430 kg/m 3 (similar to Earth) Earth is only denser because of gravitational compression Mass of Earth is greater Metals compressed to higher densities Mercury has proportionally much more metal. Weak magnetic field (1/100 of Earth s) little molten metal OR due to slow spin

14 15 Interior Structure Earth uncompressed = 4400 kg/m 3 Mercury uncompressed = 5300 kg/m 3 Mercury formed closer to the Sun, where higher temperature favored the condensation of heavier, metallic elements

15 16 Mercury Messenger Launched August 2004 Arrives

16 17 Messenger Fly-by August 2, 2005

17 18 The central core of Mercury is probably composed of A. water and CO 2 ices. B. molten rock. C. solid rock. D. solid or molten iron. 85% 3% 7% 6% A. B. C. D.

18 19 Interior Structure of Venus Mass, size and density (5340 kg/m 3 ) similar to Earth Composition and internal structure likely similar No magnetic field Due to slow rotation? P spin = 243 days

19 20 Venus Magellan

20 21 No Plate Tectonics No long ridges or faults indicating plate tectonics Many local deformations of surface, but not due to plate tectonics

21 23 Volcanoes on Venus Over 1600 major volcanoes observed Many similar to shield volcanoes on the Earth (e.g. Hawaii) May currently be active Sulfur dioxide in atmosphere Image 83 x 73 km

22 25 Coronae Large up-welling of mantle Volcanoes in and around coronae Unique to Venus Boann Corona Diameter: 225 km

23 26 Lava Channels, Lo Shen Valles ~22x27 km

24 27 Craters on Venus ~1000 craters observed on surface. Randomly distributed on surface = surface all about the same age. Surface about 500 million years old.

25 28 Venus and Earth have similar A. mass, density, and surface temperature. B. mass and density. C. mass, density, and magnetic field. 93% D. magnetic field, surface temperature, and atmosphere. 0% 3% 4% A. B. C. D.

26 29 Composition of Mars No global magnetic field P spin = 24.6 hours = 3900 kg/m 3 Some metal in the core but not liquid. interior is mainly rock compared to Venus and Earth.

27 30 General Surface Features Northern Hemisphere = lowlands Few craters = younger surface Lower average elevation Evidence for geologic activity Southern Hemisphere = highlands Many craters = much older surface Age ~3-4 byrs Google Mars Map

28 31 Volcanoes on Mars Volcanoes mainly found in Northern Hemisphere. Largest = Olympus Mons Diameter = 600 km Height = 24 km Very few craters on surface Possibly younger than 100 million years! No evidence for plate tectonics Volcanoes likely formed by hot-spot volcanism

29 32 Tharsis Region Twelve orbits a day provided the Mars Global Surveyor MOC wide angle cameras a global snapshot of weather patterns across the planet in April, Here, bluish-white water ice clouds hang above the Tharsis volcanoes. This computer generated image was created by wrapping a global map onto a sphere. The center of this sphere is 15 degrees North latitude, 90 degrees West longitude. This perspective rotates the south pole (which has no data coverage in the original map) away from our field of view. Courtesy NASA

30 33 Olympus Mons Size of Missouri 3 times height of Mt. Everest.

31 34 Tharsis Volcanoes This is a shaded relief image derived from Mars Orbiter Laser Altimeter data, which flew onboard the Mars Global Surveyor. Courtesy NASA

32 35 Valles Marineris Large canyon (fracture?) in crust 1/5 circumference of planet 7 km deep 4 minute tour

33 36 Comparison of Inner Planet Geologies

34 37 Mars has a rotation period of 24.6 hours and a density of 3900 kg/m 3 but it has no global magnetic field. What is its most probable interior composition? A. Very little metal, solid rock. 80% B. Very little metal, molten rock. C. Mostly molten metal but with solid rock. D. Mainly molten metal and molten rock. 10% 8% 1% A. B. C. D.