For Wednesday, Mar. 12

1. For Wednesday, Mar. 12 Read Section 7.5 (including Math Tools 7.2, 7.3) Assignments: Article Selection #1 (due today) Homework #4 (due Wed. Mar. 12) Mini-Project #3 (due Mon. Mar. 17)

2. Nebular Theory • idea that clouds of gas can form stars and planets ORION NEBULA (about 24 light-years across)

3. Starting Conditions ORION NEBULA Giant Molecular Clouds: • COLD (10-30 K) • LARGE (102s of light-years across, 106 MSun) • CHEMICAL COMPOSITION: 98% H and He 1.4% “ices” 0.4% “rock” 0.2% metal • cloud probably needs to be “nudged” to start forming stars

4. THE HORSEHEAD NEBULA • about 3.5 light-years across (about same as distance from Sun to nearest star… 5500x larger than solar system)

5. ROTATING DISK CONDENSATION ACCRETION CLOUD COLLAPSE GAS CAPTURE? Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds • planets orbit in same direction and same plane • Sun and planets rotate in same direction • disks seen around other stars • terrestrial planets and asteroids near Sun • jovian planets, icy moons, comets farther away • many meteorites are made of smaller bits • heavy cratering on oldest planet surfaces • asteroids, comets are “leftovers” • Jupiter, Saturn are mostly hydrogen and helium

6. CLOUD COLLAPSE Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds

7. Conservation Laws Specific combinations of variables have the property of keeping the SAME TOTAL VALUE before and after collisions, etc. MASS: stuff doesn’t disappear just because there is a collision…

8. Angular Momentum The larger the angular momentum, the harder it is to stop spinning or revolving • m: mass of object • v: speed of orbit or rotation • : angle between velocity arrow and radius line • r: distance from center of motion CONSERVATION OF ANGULAR MOMENTUM: amount does not change unless a twisting force (torque) acts on the object

9. Thought Question: Your daring professor sits in the “CHAIR OF DEATH” and starts rotating with his arms outstretched. If he pulls his arms in toward his body, and then moves them back to their original position, what will happen? • He will be spinning noticeably slower at the end. • He will be spinning at about the same speed at the end. • He will be spinning noticeably faster at the end. • Something horrible will happen…

10. Thought Question: If your daring professor sits in the “CHAIR OF DEATH” and starts rotating, what will happen if he moves his arms up and down parallel to his spin axis? • He will start to spin much slower. • He will keep spinning at the same speed. • He will start to spin much faster. • Something horrible will happen…

11. Cloud Collapse • Cloud starts out with a tiny rotation… • Gas falling toward axis starts rotating faster • Gas falling along axis doesn’t rotate faster • Faster rotation helps some gas start to orbit CONSERVATION OF ANGULAR MOMENTUM: SIDE VIEWS:

12. The Rotating Disk ORION NEBULA Part of cloud becomes flattened disk …seen around other stars

13. Conservation of Angular Momentum

14. Thought Question: Comet Halley has its perihelion at about 0.7 AU, and its aphelion at about 35 AU. How will its speed at perihelion compare to its speed at aphelion? rA rP Sun

15. ROTATING DISK CLOUD COLLAPSE Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds • planets orbit in same direction and same plane • Sun and planets rotate in same direction • disks seen around other stars

16. Heating CONSERVATION OF ENERGY: • As gas crashes together, it heats up… • (potential kinetic energy) • center of disk gets hottest COOLEST HOTTEST SIDE VIEW

17. Thought Question: As planets were beginning to form in the outer solar system (where jovian planets are today), what kinds of solid particles were probably present? snowflakes (icy material) only. dirt (rocky and metallic material) only. dirt and snowflakes.

18. For Friday, Mar. 14 Read Sections 8.1, 8.2, Math Tools 8.1 Assignments: Homework #4 (due today) Mini Project #3 (due Mon. Mar. 17) Article Outline #1 (due Fri. Mar. 21)

20. Star Formation ORION NEBULA

21. Star Formation • newborn stars are usually embedded in clouds

22. Star Formation • newborn stars are usually embedded in clouds

23. tiny dirt particles formed from condensed rock/metal • tiny ice crystals condensed from hydrogen compounds like water… but ONLY far from Sun

24. Raw Materials for Planets • most abundant raw materials: • H, He gases • “ices” (hydrogen compounds) • rock and metal

25. Condensation • Inner solar system: rocky, metallic dust condensed together into small objects meteorite cut-away:

26. ROTATING DISK CONDENSATION CLOUD COLLAPSE Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds • planets orbit in same direction and same plane • Sun and planets rotate in same direction • disks seen around other stars ion tail (from ices) • terrestrial planets and asteroids found near Sun • jovian planets, icy moons, comets found farther away

27. Accretion “Sticky” collisions of dust and snowflakes make bigger particles: Planetesimals(like asteroids and comets: several km across) slowly form, until gravity is strong enough to help pull them together: Largerprotoplanetsslowly form from these collisions:

28. Thought Question: Imagine the young solar system had a disk of orbiting dirt and ice particles. Before gravity started playing a big role, particles had to collide and stick together to make larger objects. As time went on, new collisions happened more and more frequently. at about the same rate. less and less frequently.

29. Accretion • many small objects collect into just a few large ones • collisions become less frequent • “HEAVY BOMBARDMENT”early in history

30. ROTATING DISK CONDENSATION ACCRETION CLOUD COLLAPSE Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds • planets orbit in same direction and same plane • Sun and planets rotate in same direction • disks seen around other stars • terrestrial planets and asteroids found near Sun • jovian planets, icy moons, comets found farther away • many meteorites are made of smaller bits • heavy cratering on oldest planet surfaces • asteroids, comets are “leftovers”

31. Gas Capture computer simulation: Cores of jovian planets are large enough that their gravity captures and holds gas (hydrogen and helium) gap created by planet

32. Thought Question: If the jovian planets had not been able to capture H and He gases, about how many times smaller would their masses have been? • About ½ the mass. • About 3/7ths the mass. • About 1/49th the mass. • About 1/200th the mass.

33. ROTATING DISK CONDENSATION ACCRETION CLOUD COLLAPSE GAS CAPTURE? Formation of the Solar System STEPS: EVIDENCE: • young stars seen in collapsing gas clouds • planets orbit in same direction and same plane • Sun and planets rotate in same direction • disks seen around other stars • terrestrial planets and asteroids found near Sun • jovian planets, icy moons, comets found farther away • many meteorites are made of smaller bits • heavy cratering on oldest planet surfaces • asteroids, comets are “leftovers” • Jupiter, Saturn are mostly hydrogen and helium

34. Leftovers Gas is eventually captured or pushed out by wind from the star, but dust and planetesimals are left around

36. For Monday, Mar. 17 Reading: Section 8.3 (up to “Most Planets Generate Their Own Magnetic Fields”), Math Tools 8.2 Assignments: Mini-Project #3 (due Mon. Mar. 17) Article Outline #1 (due Mon. Mar. 24)

37. SUN +JUPITER + EARTH Illustration of Kepler planet candidates blocking their stars

38. Transits - A Kind of Eclipse • planet crosses in front of a star, making star appear fainter 1130 planets detected so far!

39. Planet Transits amount of starlight blocked tells us about size of planet: VIEW FROM EARTH: star planet

40. Thought Question Most planets that have been discovered around other stars are thought to be like Jupiter. The Sun is about 11 times the size of Jupiter. What fraction of the Sun’s light would get blocked if we were watching Jupiter transit the Sun from far away? 99% 90% 10% 1% 0.1% 0.01% star planet

41. Questions!!! • Why are some jovian planets found near their stars? (“Hot Jupiters”) • Do jovian planets form differently than we think? • Did jovian planets “migrate” in toward their stars? • Why doesn’t everything have the “special direction”? • Why are Venus and Uranus rotating differently? • Why do some planets orbit in the opposite way that their stars rotate? What are “super Earths” and “mini-Neptunes”? Will terrestrial planet discoveries reveal something completely new? Why are some jovian planets found far from their stars?

42. Planets around Other Stars • Kepler 10b: • about 1.4x Earth’s size, 4.6x Earth’s mass • orbits in 45 days! • What is its surface like?

43. “Super Earths” • density similar to terrestrial planets • up to about 10 Earth’s mass (but less than Uranus and Neptune) • How common are they? • How do they form? • What could they be like?

44. still looking for these!!

45. Comparative Planetology Questions: • How are planets similar and different?  surface  atmosphere • Why are they different?

46. Uncovering Planet History CRATERING: • All planets heavily bombarded in past… • If a planet has craters today: • surface wasn’t completely protected (by atmosphere or oceans) • surface wasn’t “cleaned” recently (erosion, lava flows, or tectonics) • Look at: • how heavily cratered surface is • where craters are

47. Thought Question: D (lava flow from another volcano) C (crater) B (crater) A (volcano) What is the order from oldest to youngest?

48. Impact Craters

49. Mercury: heavily cratered, but how long ago?

50. Oldest Known Crystal4.374±0.006 billion yr old