1. Studying for Exam II, etc. Same type of exam as first one Chapters covered: Sec. 0.4, Ch.1, Ch. 4, not Ch. 5 Note: also Triangulation and Measurement covered, but not terrestrial atmospheres March 31 (iSkylab due!) Reading: Section 10.1 “The Solar Neighborhood” plus Warm-up Friday, April 4: Class canceled (Conference)

2. Meteor Showers – caused by comets RadiantDuration Quadrantids (QUA)Dec. 28-Jan. 7 Lyrids (LYR)Apr. 16-25 Eta AquaridsApr. 21-May 12 Beta TauridsJune 30 Delta Aquarids July 25-31 Perseids (PER) Aug. 10-14 Draconids Oct. 6-10 Orionids (ORI) Oct. 15-29 TauridsOct.12- Dec 2 Leonids (LEO) Nov. 14-20 Geminids (GEM)Dec. 6-19

3. Meteors, Meteroids and Meteorites A Meteor is a sudden strike of light in the night sky A Meteoroid is a small asteroid, less than 100 m in diameter A Meteorite is any piece of interplanetary matter that survives the passage through Earth’s atmosphere and lands on Earth’s surface

4. Meteors and Meteorites Small particles that strike the atmosphere Come from fragments of asteroids, Moon, Mars, comets Strike the earth all the time (“meteorites”) –High speed means lots of energy released on impact

5. Impact Craters Quebec's Manicouagan Reservoir. Large meteorite landed about 200 million years ago. The lake, 45 miles in diameter, now fills the ring. Barringer Crater, AZ 0.8 mi diameter, 200 yd deep; produced by impact about 25,000 years ago

6. Tunguska ~30 m body struck Siberia in 1908 Energy equal to that of a 10 Megaton bomb! Detonation above ground; several craters

7. Frequency of Impact Events

8. Formation of the Solar System Features to explain: –planets are far apart, not bunched together –orbits of planets are nearly circular –orbits of planets lie mostly in a single plane –directions of revolution of planets about Sun is the same, and is the same as the direction of the Sun's rotation –directions of rotation of planets about their axes is also mostly in the same direction as the Sun's (exceptions: Venus, Uranus, Pluto) –most moons revolve around their planets in the same direction as the rotation of the planets –differentiation between inner (terrestrial) and outer (Jovian) planets –existence and properties of the asteroids –existence and properties of the comets

9. Formation of the Solar System Condenses from a rotating cloud of gas and dust –Conservation of angular momentum flattens it Dust helps cool the nebula and acts as seeds for the clumping of matter

10. Formation of Planets Orbiting dust – planitesimals Planitesimals collide Different elements form in different regions due to temperature Asteroids Remaining gas

11. Structure of the Planets explained Temperature and density of materials drop with distance to sun

12. Cleaning up the Solar System Small objects are forced out of the inner Solar System by gravitational pull of bigger planets Small planetesimals collide and form planets -- or are thrown out!

13. The Earth-Moon System Earth/Moon radius: ¼ Earth/Moon mass: 1/81 Earth-Moon distance: 384,000 km

14. Features of the Earth & Moon Mass: Earth: 6  10 24 kg Moon: 1/81 Earth’s Radius: Earth: 6400 kmMoon: 1/4 Earth’s ra Density: Earth: 5500 kg/m 3 Moon: 3300 kg/m 3 –5.5 times that of water –About 2 times that of a rock Gravity: Earth: 9.8 m/s 2 Moon: 1/6 Earth’s gravity (about the same as in water)

15. Earth’s Atmosphere 78% Nitrogen, 21% Oxygen, 1% Other Troposphere – region of weather Stratosphere – stable and calm Ionosphere – gases charged by interaction with radiation from space

16. Ozone Layer (O 3 ) Absorbs most UV radiation from the Sun Hole over Antarctic –Chlorofluorocarbons (CFC’s) – released by spray cans, refrigerators

17. Magnetic field/shield: Motion of Charged Particles Charged particles “trapped” by magnetic fields Origin of the Van Allen radiation belts Protects us!

18. Moon: Large-Scale Features “Maria” –Dark areas resembling oceans –Plains of solidified lava –Part of the lunar mantle –About 3.2–3.9 billion years old Highlands (“Terrae”) –Light-colored, resemble continents –The lunar crust –More than 4 billion years old

19. The Moon – Far Side Can be seen by satellites only

20. The Mountains of the Moon Especially well visible near the terminator – the borderline between light and shadow

21. Structure of the Moon Also consists of crust, mantle and core No hydrosphere, magnetosphere or atmosphere Little seismic action

22. Tides Daily fluctuations in the ocean levels Two high and two low tides per day A result of the difference in gravitational pull from one side of the Earth to the other –F = G M m / R 2

23. Lunar Craters Old scars from meteoroid impacts Lots of them; all sizes –Copernicus ~ 90 km across –Reinhold ~ 40 km across –Also craters as small as 0.01 mm!

24. Ages of the Earth and Moon Determined by radioactive dating –Compare amount of radioactive material with amount of decay product –Useful isotopes: Uranium-238 (half-life 4.5 billion years) Uranium-235 (half-life 0.7 billion years) For shorter time scales, Carbon-14 (5730 years) Oldest surface rocks on Earth (Greenland, Labrador) about 3.9 billion years old –When rocks solidified Lunar highlands: 4.1–4.4 billion years old –Rocks from lunar maria slightly younger, more recently melted Meteorites: 4.5 billion years old –Date to origin of solar system

25. Mercury Small, bright but hard to see About the same size as the moon Density about that of Earth Day ~ 59 Earth days Year ~ 88 Earth days

26. Venus Bright, never very far from the sun –“Morning/Evening star” Similar to Earth in size and density Day ~  243 Earth days (retrograde!) Year ~ 225 Earth days

27. Venus Very thick atmosphere, mostly CO 2 Heavy cloud cover (sulfuric acid!) –About 90 times the pressure of Earth’s atmosphere –Very strong greenhouse effect, surface temperature about 750 K No magnetic field

28. Surface Features Two large “continents” –Aphrodite Terra and Ishtar Terra –About 8% of the surface Highest peaks on Aphrodite Terra rise about 14 km above the deepest surface depression –Comparable to Earth’s mountains

29. Hothouse Venus: 850 °F

30. Mars Fairly bright, generally not too hard to see Smaller than Earth Density similar to that of the moon Surface temperature 150–250 K Day ~ 24.6 hours Year ~ 2 Earth years Thin atmosphere, mostly carbon dioxide –1/150 the pressure of Earth’s atmosphere Tiny magnetic field, no magnetosphere

31. Mars Northern Hemisphere basically huge volcanic plains –Similar to lunar maria Valles Marineris – Martian “Grand Canyon” –4000 km long, up to 120 km across and 7 km deep –So large that it can be seen from Earth

32. Martian Volcanoes Olympus Mons –Largest known volcano in the solar system –700 km across at base –Peak ~25 km high (almost 3 times as tall as Mt. Everest!)

33. Martian Seasons: Icecaps & Dust Storms

34. Martian Surface Iron gives the characteristic Mars color: rusty red! View of Viking 1 1 m rock Sojourner

35. Water on Mars? Mars Louisiana Outflow Channels Runoff channels

36. Life on Mars? Giovanni Schiaparelli (1877) – observed “canali” (channels) on Martian surface Interpreted by Percival Lowell (and others) as irrigation canals – a sign of intelligent life Lowell built a large observatory near Flagstaff, AZ (Incidentally, this enabled C. Tombaugh to find Pluto in 1930) Speculation became more and more fanciful –A desert world with a planet-wide irrigation system to carry water from the polar ice caps? –Lots of sci-fi, including H.G. Wells, Bradbury, … All an illusion! There are no canals…

37. Viking Lander Experiments (1976) Search for bacteria- like forms of life Results inconclusive at best

38. Atmospheric Histories Primary atmosphere: hydrogen, helium, methane, ammonia –Too light to “stick” to a planet unless it’s very big  Jovian Planets Secondary atmosphere: water, CO 2, SO 2, … –Outgassed from planet interiors, a result of volcanic activity

39. Atmospheric Histories - Venus Venus is closer to Sun than Earth  hotter surface Not a lot of liquid water on surface initially CO 2 could not be absorbed by water, rocks because of higher temperatures  run-away Greenhouse effect: it’s hot, the greenhouse gases can’t be be stored away, it gets hotter …

40. Earth’s Atmospheric History Volcanic activity spews out water steam Temperature range allowed water to liquify CO 2 dissolves in oceans, damping greenhouse effect More water condenses, more CO 2 is absorbed If too cold, ice forms  less cloud cover  more energy No oxygen at this point, since it would have been used up producing “rust” Tertiary atmosphere: early life contributes oxygen –1% 800 Myrs ago, 10% 400 Myrs ago

41. Mars – Freezing over Mars once had a denser atmosphere with liquid water on the surface As on Earth, CO 2 dissolves in liquid water But: Mars is further away from the Sun  temperature drops below freezing point  inverse greenhouse effect permafrost forms with CO 2 locked away Mars probably lost its atmosphere because its magnetic field collapsed, because Mars’ molten core cooled down

42. Greenhouse Effect Earth absorbs energy from the Sun and heats up Earth re-radiates the absorbed energy in the form of infrared radiation The infrared radiation is absorbed by carbon dioxide and water vapor in the atmosphere

43. Global Warming Excessively “politicized” topic Very complex problem scientifically Slow changes over long periods of time Sources of heating, sources of cooling themselves are temperature dependent

44. Data is not enough – need to understand how to interpret it correctly

45. Noise vs Signal, Long term vs Short term

46. Man-made CO 2 in the Atmosphere goes up

47. Correlation: Temperatures rise when Carbon Dioxide levels rise This is true since prehistoric times