Starry Monday at Otterbein

1. Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the month- October 1, 2007 Dr. Uwe Trittmann

2. Today’s Topics • Atmospheric Histories – Or: Is the Greenhouse Effect positive or negative? • The Night Sky in October

3. Feedback! • Please write down suggestions/your interests on the note pads provided • If you would like to hear from us, please leave your email / address • To learn more about astronomy and physics at Otterbein, please visit • http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.) • http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)

4. Obviously … • No “Greenhouse Effect” without greenhouse – need an atmosphere • But: atmospheric histories possible without atmosphere! (it could have vanished) • “Positive” and “negative” have a colloquial and a scientific meaning

5. 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

6. Greenhouse Effect • By “absorption” we mean that the radiation’s energy get stored in the molecule • The molecule has now more energy, corresponding to a higher temperature

7. Positive, negative and runaway Greenhouse Effects • Positive greenhouse effect heats up a surface from the temperature that it normally would have • Earth would be 74 F colder without it • Cooling effects are sometimes called a “negative” or “inverse” greenhouse effect • Runaway greenhouse effects get stronger as the temperature gets up, e.g. because this releases more greenhouse gases • If you like it cooler, a positive greenhouse effect could be “negative” 

8. Overview: The Solar System

9. Contents of the Solar System • Sun • Planets – 9 known (now: 8) • Mercury, Venus, Earth, Mars (“Terrestrials”) • Jupiter, Saturn, Uranus, Neptune (“Jovians”) • Pluto (a Kuiper Belt object; officially a “dwarf planet” ) • Natural satellites (moons) – over a hundred • Asteroids and Meteoroids • 6 known that are larger than 300 km across • Largest, Ceres, is about 940 km in diameter • Comets • Rings • Dust

10. Size matters: radii of the Planets Typically: larger radius larger volume larger mass larger gravitational pull

11. The Terrestrial Planets • Small, dense and rocky, solid surface Mercury Mars Venus Earth

12. The Jovian Planets • Large, made out of gas, and low density, no solid surface Saturn Jupiter Neptune Uranus

13. All Planets were formed from the same gas cloud at the same time • Formation of the Solar System from a rotating cloud of gas and dust • Dust helps cool the nebula and acts as seeds for the clumping of matter Why are the planets so different?

14. Differences of the Planets explained Temperature and density of materials drop with distance to sun 32ºF

15. Atmospheric Histories • Primary atmosphere: “primordial” materials: hydrogen, helium; plus: methane, ammonia • Too light to “stick” to a planet unless it’s very big  Jovian Planets • Secondary atmosphere: water, CO2, SO2, … • Outgassed from planet interiors, a result of volcanic activity • Tertiary atmosphere: changes due to biological activities on surface

16. Current Atmospheres • Mercury, Moon  (and most moons), asteroids:no atmosphere! • Note the soft edges of the crater erosion without atmosphere!

17. Venus’ current Atmosphere • 96.5% CO2, 3.5% Nitrogen at 90 times Earth’s atmospheric pressure; sulfuric acid clouds • View from Russian probe Venera 14 (1975)

18. Hothouse Venus: 870 °F – liquid lead!

19. Current Atmosphere of Earth • 78% Nitrogen, 21% Oxygen, 1% Other • Most “other” is Argon! • Troposphere – region of weather • Stratosphere – stable and calm • Ionosphere – gases charged by interaction with radiation from space

20. Ozone Layer (O3) • Absorbs most UV radiation from the Sun • Hole over Antarctic • Chlorofluorocarbons (CFC’s) – released by spray cans, refrigerators • Ozone at ground level is a pollutant!

21. Mars’ current atmosphere • 95% CO2, 3% Nitrogen at less than 1% of Earth’s atmospheric pressure

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

23. Martian Seasons: Icecaps & Dust Storms

24. Jupiter’s Atmosphere • Cloud bands parallel to equator • Great Red Spot • First observed in 1664 by Robert Hooke

25. Jupiter’s Atmosphere • 86% Hydrogen, 14% Helium; some methane, water, ammonia • Several layers of clouds: ammonia, ammonium hydrosulfide, water • Colors mostly due to compounds of sulfur and phosphorus

26. Great Red Spot • About twice the diameter of the Earth • A hurricane that is hundreds of years old!

27. Saturn’s Atmosphere • 92% Hydrogen 7% Helium; some methane, water, ammonia • Belt structure similar to Jupiter’s, but fainter • Storms are rarer • White spot seen, 1990 (Voyager)

28. Uranus’ and Neptune’s Atmospheres Neptune’s Dark Spot • Ammonia frozen out; more methane • Methane absorbs red light, leads to bluish color • Almost no band structure on Uranus

29. Jupiter’s moon Io • The most volcanically active object in the solar system • Heated by tidal friction • Eruptions as high as 200 miles, may last for months • No atmosphere

30. Saturn’s Moon Titan • Titan is the only moon in the solar system known to have an atmosphere Infrared picture shows surface details

31. 2005 Huygens Landing • STRANGE TITAN: Get ready for two of the strangest hours in the history of space exploration. That's how long it will take the European Space Agency's Huygens probe to parachute to the surface of Saturn's largest moon Titan on January 14th. Huygens will sample Titan's atmosphere, photograph its bizarre terrain, listen for alien sounds and, possibly, splash down in a liquid methane sea.

33. Landing Site on Titan • Rocks made from methane ice

34. 360° Panorama of Titan

35. Atmospheric Histories - Venus • Venus is closer to Sun than Earth hotter surface • Not a lot of liquid water on surface initially • CO2 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 …

36. Earth’s Atmospheric History • Volcanic activity spews out water steam • Temperature range allowed water to liquify • CO2 dissolves in oceans, damping greenhouse effect • More water condenses, more CO2 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

37. Mars – Freezing over • Mars once had a denser atmosphere with liquid water on the surface • As on Earth, CO2 dissolves in liquid water • But: Mars is further away from the Sun  temperature drops below freezing point  inverse greenhouse effect • permafrost forms with CO2 locked away • Mars probably lost its atmosphere because its magnetic field collapsed, because Mars’ molten core cooled down

38. Global Warming on Earth • Excessively “politicised” topic • Very complex problem scientifically • Slow changes over long periods of time • Could use more data • Sources of heating, sources of cooling are temperature dependent

39. Hard Facts: Measurements • Undisputed: global temperatures go up

40. Man-made CO2 in the Atmosphere goes up

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

42. The Last Millennium – “Hockey Stick”

43. Is it for real? • Virtually everyone agrees that average global temperatures have risen by about 1 °F over the last century • May not sound like much, but during the last ice age average temperatures were only about 8-9 F colder than now • Real question: is it due to human activity (the greenhouse gases) or just natural variation? • IPCC report • “Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.”

44. A lot of human activities release greenhouse gases • No easy political solution  need concerted, global, long term initiative

45. Possible Effects • Rising sea levels and inundation of coastal areas • But not: ocean front properties in Kansas in 20 years! • More extreme weather (e.g. droughts followed by periods of heavy rainfall and flooding, hurricanes, monsoons, etc.) • Disruption of agriculture • Increases in malaria and other insect-borne diseases • …

46. Observing Inner and Outer Planets • Inner Planets: closer to sun than Earth • Mercury & Venus • Always close to sun in the sky • Outer Planets: further from sun than Earth • Mars, Jupiter, Saturn, Uranus, Neptune, Pluto • Best viewing when opposite of sun in the sky

47. Inner Planets superior conjunction Inner planet western elongation eastern elongation inferior conjunction Earth

48. conjunction Outer Planets quadrature Earth quadrature Outer planet opposition

49. Close Outer Planet Size of planet varies a lot as Earth moves Earth Outer planet

50. Far-Out Planet Earth Size of planet varies little as Earth moves Outer planet