Homework #3

1. Homework #3 Homework #3 is due Tuesday, October 9.

2. Standing on a Comet What the $&*^%#

4. Io  no impact craters  most volcanic body in the solar system (>300 active volcanoes)  significant tidal heating

5. Plumes can reach 300 km above the surface, implying ejection velocities of ~1 km/s, 10 times higher than the most violent volcanoes on Earth.

6. Europa Surface is almost entirely frozen water, brown regions show small deposits of rocky material. Liquid ocean underneath? HST showed that Europa has a very tenuous oxygen atmosphere, one of only 5 moons in the Solar System to harbor an atmosphere. Most likely to harbor life outside of Earth. “Attempt No Landing There”

7. Ganymede Dark terrain (older), bright terrain Young craters show highly reflective freshly exposed ice

8. Callisto Heavily cratered but there is a deficit of small craters. Perhaps the most heavily-crated object in the Solar System

9. 79 moons discovered to date. Most in solar system.

10. Saturn • Giant and gaseous like Jupiter • Spectacular rings • Many moons, including cloudy Titan

11. Only 2/3 as dense as water!

12. September 2009

13. Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon. Artist’s conception

14. Each “ring” composed of many may “ringlets”.

15. Titan •  900 km thick atmosphere •  pressure at surface is 50% greater than Earth’s • atmosphere is 98% composed of N probably from NH3 photodissociation, but also hydrocarbons • you could almost fly by flapping your arms!

16. Uranus • Smaller than Jupiter/Saturn; much larger than Earth • Made of H/He gas and hydrogen compounds(H2O, NH3, CH4) • Extreme axis tilt • Moons and rings • Excess methane gives bluish color

17. Uranus spins on its side – rotational axis points toward Sun

18. ~42 years of continuous daylight followed by ~42 years of continuous night at poles.

19. occultation

20. Five major moons of Uranus

21. Neptune • Similar to Uranus (except for axis tilt) • Many moons (including Triton)

22. Same surface gravity as Earth (if it had a solid surface)

23. Neptune rings system Voyager 2

24. Triton Retrograde orbit, 23o inclination; if captured is the largest captured moon. Smooth young terrain is consistent with recent geological activity resulting from tidal heating from Neptune after being captured.

25. Chapter 8Formation of the Solar System

26. What properties of our solar system must a formation theory explain? • Patterns of motion of the large bodies • Orbit in same direction and plane • Existence of two types of planets • Terrestrial and Jovian • Existence of smaller bodies • Asteroids and comets • Notable exceptions to usual patterns • Rotations of Uranus and Venus, Earth’s Moon

27. Motion of Large Bodies • All large bodies in the solar system orbit in the same direction and in nearly the same plane. • Most also rotate in that direction.

28. Orbital Plane of Solar System

29. What properties of our solar system must a formation theory explain? • Patterns of motion of the large bodies • Orbit in same direction and plane • Existence of two types of planets • Terrestrial and jovian • Existence of smaller bodies • Asteroids and comets • Notable exceptions to usual patterns • Rotations of Uranus and Venus, Earth’s Moon

30. Two Major Planet Types • Terrestrial planets made of rock/metal (high density), relatively small, and close to the Sun with few/no moons and no rings. • Jovian planets are gaseous (low density), larger, and farther from the Sun with many moons and rings.

31. What properties of our solar system must a formation theory explain? • Patterns of motion of the large bodies • Orbit in same direction and plane • Existence of two types of planets • Terrestrial and jovian • Existence of smaller bodies • Asteroids and comets • Notable exceptions to usual patterns • Rotations of Uranus and Venus, Earth’s Moon

32. Swarms of Smaller Bodies • Many rocky asteroids and icy comets populate the solar system. Asteroid Belt – between Mars and Jupiter Kuiper Belt – outside Neptune’s orbit (including Pluto) Oort Cloud – ~50,000 AU or about a light year (not actually discovered yet)

33. What properties of our solar system must a formation theory explain? • Patterns of motion of the large bodies • Orbit in same direction and plane • Existence of two types of planets • Terrestrial and jovian • Existence of smaller bodies • Asteroids and comets • Notable exceptions to usual patterns • Rotations of Uranus and Venus, Earth’s Moon

34. What theory best explains the features of our solar system? • The nebular theorystates that our solar system formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula. (Nebula is the Latin word for cloud.) • Kant and Laplace proposed the nebular hypothesis over two and a half centuries ago. • A large amount of evidence now supports this idea.

35. Close Encounter Hypothesis • A rival idea proposed that the planets formed from debris torn off the Sun by a close encounter with another star. • That hypothesis could not explain observed motions and types of planets. • Survived well into the 20th century before losing favor

36. Galactic Recycling • Elements that formed planets were made in stars and then recycled through interstellar space. • Sun is a second or third generation star to explain ~1-2% metal content of the Solar System. • First generation of stars should have no terrestrial planets!

37. What caused the orderly patterns of motion in our solar system?

38. Conservation of Angular Momentum • Rotation speed of the cloud from which our solar system formed must have increased as the cloud contracted. Mass x velocity x radius = constant as radius velocity

39. Rotation of a contracting cloud speeds up for the same reason a skater speeds up as she pulls in her arms. Cloud initially a light year or so in diameter.

40. Collisions between gas particles in cloud gradually reduce random motions.

41. Flattening • Collisions between particles in the cloud caused it to flatten into a disk (rather than gravity pulling it down into a disk).

42. Why are there two major types of planets?

43. Conservation of Energy As gravity causes cloud to contract, it heats up. Gravitational potential energy  kinetic energy of gas  thermal energy via collisions.

44. Temperature distribution during early Solar System Nebula core is dense – collapses fast and first to form Sun. Solar environment is hot; it's cooler further out.

45. Inside the frost line: too hot for hydrogen compounds to form ices – water/CO2/methane stays in vapor form Outside the frost line: cold enough for ices to form

46. Temperature determines what can condense (gas to solid) to form seeds of planets at a given distance from Sun. Rock can be solid at much greater temperatures than ice. ➢ inside 0.3 AU – too hot for anything to condense ➢ only metals (Ni, Fe) close in (only need T<1300K) ➢ metals, plus rocks (minerals) further out (some condense even at T=500K) – out to ~3.5 AU ➢ metals plus rocks, plus ices (CH4, NH3, H2O) beyond the frost line (need T<150K) – beyond 3.5 AU There are rock + metals everywhere in Solar System (outside 0.3 AU), but ice only exists outside frost line (~3.5 AU)

47. H & He never condense to solid - they are always a gas!! Planetesimals form by accretion – a growth by collision (electrostatic force then gravitational force) Inside frost line we get rock/metal “seeds”. That's only 0.6% of all the stuff there. The planetesimals are small, and it's too hot to pull in H & He Outside the frost line we get rock/metal and ices – 2% of all stuff; planetesimals are larger, and it's cool (and massive) enough to pull in H & He

48. Gravity draws planetesimalstogether to form planets. This process of assembly is called accretion.

49. Dust grain – 0.02mm across from interplanetary space