September 26, 2011: 10am Class

1. September 26, 2011: 10am Class Please pick up papers along side of wall Today: Starry Night homework Mars Asteroids and Meteorites

2. See class notes for Aug. 26At the North Pole:

3. At the Equator

5. Viking’s View of VallesMarineris

6. Cratering on Mars • The amount of cratering differs greatly across Mars’s surface. • Many early craters have been erased.

7. What geological evidence tells us that water once flowed on Mars?

8. Dry Riverbeds? • Close-up photos of Mars show what appear to be dried-up riverbeds.

9. Erosion of Craters • Details of some craters suggest they were once filled with water.

10. Martian Rocks • Mars rovers have found rocks that appear to have formed in water.

11. Hydrogen Content • Map of hydrogen content (blue) shows that low-lying areas contain more water ice.

12. Crater Walls • Gullies on crater walls suggest occasional liquid water flows have happened less than a million years ago.

13. Small spherical rocks called “blueberries” are thought to be deposits formed by water

14. Judging from the geology of the river beds and the amount of cratering since, we estimate that liquid water was present around a billion years ago, or more, and froze and/or escaped Mars about 3 billion years ago HIRISE Video

15. Why did Mars change?

16. Changing Axis Tilt • Calculations suggest Mars’s axis tilt ranges from 0° to 60°. • Such extreme variations can cause climate changes. • Alternating layers of ice and dust in polar regions reflect these climate changes. Earth: axis tilt changes are avoided because we have a very large Moon

17. Climate Change on Mars • Mars has not had widespread surface water for 3 billion years. • Greenhouse effect probably kept the surface warmer before that. • Somehow Mars lost most of its atmosphere.

18. Climate Change on Mars • Magnetic field may have preserved early Martian atmosphere. • Solar wind may have stripped atmosphere after field decreased because of interior cooling.

19. Moons of Mars • Mars has two tiny moons: Phobos and Deimos • They look like asteroids • Phobos: 13 miles across • Deimos: 10 miles across Phobos Deimos

20. What have we learned? • What is Mars like today? • Mars is cold, dry, and frozen. • Strong seasonal changes cause CO2 to move from pole to pole • dust storms. • Why did Mars change? • Its atmosphere must have once been much thicker for its greenhouse effect to allow liquid water on the surface. • Somehow Mars lost most of its atmosphere, perhaps because of its declining magnetic field.

21. What have we learned? • What are the major geological features of Mars? • Differences in cratering across surface • Giant shield volcanoes • Evidence of tectonic activity

22. What have we learned? • What geological evidence tells us that water once flowed on Mars? • Some surface features look like dry riverbeds. • Some craters appear to be eroded. • Rovers have found rocks that appear to have formed in water. • Gullies in crater walls may indicate recent water flows.

23. “Canals” on Mars? Percival Lowell misinterpreted surface features seen in telescopic images of Mars.

24. Is there Life on Mars? Was there life in the past, when Mars had water?

25. Life on Mars? • Searches for life on Mars have yielded no evidence that life currently exists on Mars • However, we have only explored a tiny fraction of the surface of Mars • Contamination by spacecraft now a serious issue • We have discovered single-celled life forms on Earth in extreme environments: underwater heat vents, inside glaciers, etc. • Jury still out!

26. Asteroids and Meteorites

27. Asteroid Facts • Asteroids are rocky leftovers of planet formation. • Asteroids are cratered and not round. • The largest is Ceres, diameter ~1000 kilometers. • 150,000 in catalogs, and probably over a million with diameter >1 kilometer. • Small asteroids are more common than large asteroids. • All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet.

28. Asteroids with Moons • Some large asteroids have their own moon. • Asteroid Ida has a tiny moon named Dactyl.

29. Asteroid Orbits • Most asteroids orbit in the asteroid belt between Mars and Jupiter. • Trojan asteroids follow Jupiter’s orbit. • Orbits of near-Earth asteroids cross Earth’s orbit.

30. Origin of Asteroid Belt • Rocky planetesimals between Mars and Jupiter did not accrete into a planet. • Jupiter’s gravity, through influence of orbital resonances, stirred up asteroid orbits and prevented their accretion into a planet.

31. If you discover an asteroid and track its orbit, you get to name it.

32. Meteorites

33. Meteor Terminology • Meteorite: a rock from space that falls through Earth’s atmosphere • Meteor: the bright trail left by a meteorite • Falling star = meteor • Bolide = a really bright meteor

34. Near Earth Asteroids

35. Meteorite Impact Chicago, March 26, 2003

37. Meteorite Types • Primitive: unchanged in composition since they first formed 4.6 billion years ago • Processed: younger; have experienced processes like volcanism or differentiation • Stony Meteorites; Iron Meteorites

38. Stony Meteorite

39. Iron Meteorite

40. Meteorites from Moon and Mars • A few meteorites arrive from the Moon and Mars. • Composition differs from the asteroid fragments. • A cheap (but slow) way to acquire Moon rocks and Mars rocks

41. Meteor Showers • Many meteors seeming to come in along radiants

42. Meteors in a meteor shower appear to emanate from the same area of sky because of Earth’s motion through space.