Earth as a Living Planet: Key Features and Human Impact

1. ASTR100 (Spring 2006) Introduction to AstronomyEarth as a Living Planet Prof. D.C. Richardson Sections 0101-0106

2. Extra Credit Opportunities • The first 10 astronomy-related posts to the course discussion board or blog. • Existing posts will earn retroactive credit and not count against the 10. • Maximum 3 points per student. • Comments/replies can count too! • Homework #6.5 on MasteringAstronomy.com. • Not due for a couple of weeks. • Ask me an astronomy question in class, right now!

3. A Word About the Greenhouse Effect • The “greenhouse” part is misleading: • A real greenhouse works by heating and trapping the air inside the structure. • The same principle explains why the inside of a car gets hot so fast on a sunny day. • The greenhouse “effect” is trapping of heat by the air (atmosphere) itself. • No glass needed!

4. What unique features of Earth are important to human life? • Surface liquid water. • Atmospheric oxygen. • Plate tectonics. • Climate stability.

5. What unique features of Earth are important to human life? • Surface liquid water. • Atmospheric oxygen. • Plate tectonics. • Climate stability. Earth’s distance from the Sun and moderate greenhouse effect make liquid water possible.

6. What unique features of Earth are important to human life? • Surface liquid water. • Atmospheric oxygen. • Plate tectonics. • Climate stability. PHOTOSYNTHESIS (plant life) is required to make high concentrations of O2, which produces the protective layer of O3.

7. What unique features of Earth are important to human life? • Surface liquid water. • Atmospheric oxygen. • Plate tectonics. • Climate stability. Plate tectonics are an important step in the carbon dioxide cycle.

8. The Carbon Dioxide Cycle • Atmospheric CO2 dissolves in rainwater. • Rain erodes minerals that flow into the ocean. • Minerals combine with carbon to make rocks on ocean floor.

9. The Carbon Dioxide Cycle • Carbonate rocks carried down into the mantle by subduction. • Rocks melt in mantle and outgas CO2 back into atmosphere through volcanoes.

10. What unique features of Earth are important to human life? • Surface liquid water. • Atmospheric oxygen. • Plate tectonics. • Climate stability. The CO2 cycle acts like a thermostat for the Earth’s temperature.

11. The Thermostat • If Earth heats up a bit, increased rainfall dissolves more CO2, reducing greenhouse effect. • If Earth cools down a bit, decreased rainfall dissolves less CO2, building up greenhouse gas. • Everything is OK if swings are slow and small…

12. These unique features are intertwined… • Plate tectonics creates climate stability. • Climate stability allows liquid water. • Liquid water is necessary for life. • Life is necessary for atmospheric oxygen. • More?

13. How is human activity changing our planet?

14. Dangers of Human Activity • Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation. • Human activity is driving many other species to extinction. • Human use of fossil fuels produces greenhouse gases that can cause global warming.

15. Global Warming • Earth’s average temperature has increased by 0.5°C in the past 50 years. • The concentration of CO2 is rising rapidly. • An unchecked rise in greenhouse gases will eventually lead to global warming.

16. CO2 Concentration • Global temperatures have tracked CO2 concentration for the last 500,000 years. • Antarctic air bubbles indicate the current CO2 concentration is at its highest level in at least 500,000 years.

17. CO2 Concentration • Most of the CO2 increase has happened in the last 50 years!

18. Modeling of Climate Change • Complex models of global warming suggest that the recent temperature increase is indeed consistent with human production of greenhouse gases.

19. Consequences of Global Warming • Melting of polar ice. • More extreme weather. • Rising sea levels.

20. What can we do about it? • Reduce greenhouse emissions by improving energy efficiency, especially car gas mileage. • Invest in alternative energy sources. • Bury the CO2.

21. What makes a planet habitable? • Located at an optimal distance from the Sun for liquid water to exist.

22. What makes a planet habitable? • Large enough for geological activity to release and retain water and atmosphere.

23. Planetary Destiny • Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.

24. ASTR100 (Spring 2008) Introduction to AstronomyJovian Planet Systems Prof. D.C. Richardson Sections 0101-0106

25. A Different Kind of Planet • Bigger and more massive. • Lower density, different composition. • Rings. • Numerous moons.

26. Jovian Planet Composition • Jupiter and Saturn • Mostly H and He gas. • Some hydrogen compounds, metal, rock. • Uranus and Neptune • Mostly hydrogen compounds: water (H2O), methane (CH4), ammonia (NH3). • Some H, He, metal, and rock. • Why the difference?

27. Jovian Planet Formation • Beyond the frost line, planetesimals could accumulate ICE. • H compounds are more abundant than rock/metal so jovian planets got bigger and acquired H/He atmospheres.

28. Jovian Planet Formation • The jovian cores are very similar: solid masses of about 10 Earths. • The jovian differences are in the amount of H/He gas accumulated. • Why did that amount differ?

29. Differences in Jovian Planet Formation • TIMING: the planet that forms earliest captures the most H & He gas. Capture ceases after the first solar wind blows the leftover gas away. • LOCATION: the planet that forms in the densest part of the nebula forms its core first.

30. Density Differences • Uranus and Neptune are denser than Saturn because they have less H/He, proportionately.

31. Density Differences • But that doesn’t explain Jupiter’s density…

32. Sizes of Jovian Planets • Adding mass to a jovian planet compresses the underlying gas layers.

33. Sizes of Jovian Planets • Greater compression is why Jupiter is not much larger than Saturn even though it is 3 times more massive. • Jovian planets with even more mass can be smaller than Jupiter.

34. What are jovian planets like on the inside?

35. Interiors of Jovian Planets • No solid surface. • Layers under high pressure and temperature. • Cores (~10 Earth masses) made of hydrogen compounds, metals and rock. • The layers are different for the different planets. WHY?

36. Inside Jupiter • High pressure inside Jupiter causes phase of hydrogen to change with depth. • Hydrogen acts like a metal at great pressures because its electrons move freely.

37. Comparing Jovian Interiors • Models suggest that cores of jovian planets have similar composition. • Lower pressure inside Uranus and Neptune means no liquid or metallic hydrogen.

38. Jupiter’s Magnetic Field • Jupiter has a powerful magnetic field generated by its rotating, convecting layer of metallic hydrogen.

39. Aurora on Jupiter

40. Aurorae on Saturn

41. What is the weather like on jovian planets?

42. Jupiter’s Atmosphere • Hydrogen compounds in Jupiter form clouds. • Different cloud layers correspond to freezing points of different hydrogen compounds. • Other jovian planets have similar cloud layers.

43. Planet colors • Ammonium sulfide clouds reflect red/brown. • Ammonia, the highest coldest layer, reflects white. Jupiter’s Colors

44. Planet colors • Saturn’s layers are the same, but deeper in and farther from the Sun—more subdued. Saturn’s Colors

45. Uranus and Neptune’s upper layers are colder still, allowing methane to condense as clouds. • Methane gas absorbs red light and transmits blue light reflected by the lower clouds.

46. Jupiter Winds and Storms • Earth’s rotation makes storms “spin.” • Jupiter’s fast rotation stretches storms into bands that surround the planet. • High east/west winds (up to 400 km/hr).

47. Jupiter’s Great Red Spot • A storm twice as wide as Earth. • Has existed for at least 3 centuries.

48. Weather on Jovian Planets • All the jovian planets have strong winds and storms.

49. Quiz! • Take out a sheet of paper. • Write down your name and section number. • That’s it! Ha ha. • Hand it in (along with HW#6 if needed). • Have a great Spring Break! • BUT REMEMBER, THERE IS DISCUSSION TOMORROW FOR SECTIONS 105 & 106!