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

2. Jovian Planet Formation The jovian cores are very similar: ~ mass of 10 Earths The jovian differences are in the amount of H/He gas accumulated. Why did that amount differ?

3. Differences in Jovian Planet Formation _______: The planet that forms earliest captures the most hydrogen and helium gas. Capture _______ after the first solar wind blew the leftover gas away. ________: The planet that forms in a denser part of the nebula forms its core first.

4. Density Differences Uranus and Neptune are denser than Saturn because they have less H/He, proportionately. But that explanation doesn’t work for Jupiter

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

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

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

8. Comparing Jovian Interiors Models suggest that cores of jovian planets have similar composition. Lower _________ inside Uranus and Neptune mean no metallic hydrogen.

9. Inside Jupiter High pressure inside of Jupiter causes the phase of hydrogen to change with depth. Hydrogen ____ like a metal at great depths because its electrons move freely.

10. Jupiter’s Magnetosphere Jupiter’s strong magnetic field gives it an enormous magnetosphere. Gases escaping Io feed the donut-shaped Io torus. Aurora on Jupiter

11. What is the weather like on jovian planets?

12. 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.

13. Methane on Uranus and Neptune Methane gas on Neptune and Uranus absorbs red light but transmits blue light. Blue light reflects off methane clouds, making those planets look blue.

14. Jupiter’s Great Red Spot A storm ______ as wide as Earth Has existed for at least __ centuries

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

16. Sizes of Moons Small moons (< 300 km) —No geological activity Medium-sized moons (300–1,500 km) —Geological activity in past Large moons (> 1,500 km) —Ongoing geological activity

17. Small Moons Far more numerous than the medium and large moons Not enough _______ to be spherical: “potato-shaped”

18. Medium and Large Moons Enough self-gravity to be spherical Have substantial amounts of ice Formed ________ around jovian planets Circular orbits in same direction as planet rotation

19. Io’s Volcanic Activity Io is the most volcanically active body in the solar system, but why?

20. Io’s Volcanoes Volcanic eruptions continue to change Io’s surface.

21. ______________ Io is squished and stretched as it orbits Jupiter. But why is its orbit so elliptical?

22. Orbital __________ Every 7 days, these three moons line up. The tugs add up over time, making all three orbits elliptical.

23. Europa’s Ocean: Waterworld?

24. Tidal Stresses Crack Europa’s Surface Ice

25. Tidal stresses crack Europa’s surface ice Tidal flexing closes crack, grinds up ice Tidal flexing opens crack, leaving two ridges

26. Europa’s Interior Also Warmed by Tidal Heating

27. Europa Diameter 3138 km Mass 4.8 x 10 22 kg Smooth young surface Oxygen atmosphere (not of biologic origin) Ices and water? Second possible place for life in our solar system.

28. Ganymede Largest moon in the solar system Clear evidence of geological activity Tidal heating plus heat from radio- active decay?

29. Callisto “Classic” cratered iceball No tidal heating, no orbital resonances But it has magnetic field !?

30. Titan’s Atmosphere Titan is the only moon in the solar system which has a thick atmosphere. It consists mostly of nitrogen with some argon, methane, and ethane.

31. Why are jovian planet moons more geologically active than small rocky planets?

32. Rocky Planets vs. Icy Moons Rock melts at _____ temperatures. Only large rocky planets have enough heat for activity. Ice melts at _____ temperatures. Tidal heating can melt internal ice, driving activity.

33. Much farther from Sun than inner planets Mostly H/He; no solid surface ___ times more massive than Earth Many moons, rings Jupiter

34. Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons ___ (shown here): Active volcanoes all over ______: Possible subsurface ocean ________: Largest moon in solar system ________: A large, cratered “ice ball”

35. Saturn Giant and gaseous like Jupiter Spectacular _____ Many moons, including cloudy Titan Cassini spacecraft currently studying it

36. Rings are ___ solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon. Artist’s conception The Rings of SaturnRings

37. What are Saturn’s rings like? They are made up of numerous, tiny individual particles. They orbit over Saturn’s equator. They are very thin.

38. Spacecraft View of Ring Gaps

39. Gap Moons Some small moons create gaps within rings.

40. Jovian Ring Systems All four jovian planets have ring systems. Others have smaller, darker ring particles than does Saturn.

41. Why do the jovian planets have rings? They formed from dust created in impacts on moons orbiting those planets. How do we know this?

42. How do we know? Rings aren’t leftover from planet formation because the particles are too small to have survived this long. There must be a continuous replacement of tiny particles. The most likely source is impacts with the jovian moons.

43. Ring Formation Jovian planets all have rings because they possess many small moons close-in. Impacts on these moons are random. Saturn’s incredible rings may be an “accident” of our time.

44. Smaller than Jupiter/Saturn; much larger than Earth Made of H/He gas and hydrogen compounds (H 2 O, NH 3, CH 4 ) Extreme ________ Moons and rings Uranus

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

46. Radiation and outflowing matter from the Sun — the ___________ — blew away the leftover gases. The Solar WindSolar

47. Swarms of Smaller Bodies Many rocky asteroids and icy comets populate the solar system.

48. Asteroids and Comets Leftovers from the accretion process Rocky _________ inside frost line Icy ______ outside frost line

49. Asteroid Facts Asteroids are rocky leftovers of planet formation. The largest is Ceres, diameter ~1,000 km. There are 150,000 in catalogs, and probably over a million with diameter >1 km. Small asteroids are more common than large asteroids. All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet.

50. Asteroids are cratered and not round.

51. Asteroids with Moons Some large asteroids have their own moon. Asteroid Ida has a tiny moon named Dactyl.

52. Asteroid Orbits ____ asteroids orbit in a belt between Mars and Jupiter. ______ asteroids follow Jupiter’s orbit. Orbits of ____- Earth asteroids cross Earth’s orbit.

53. Orbital Resonances Asteroids in orbital resonance with Jupiter experience periodic nudges. Eventually those nudges move asteroids out of resonant orbits, leaving gaps in the belt.

54. Origin of Asteroid Belt Rocky planetesimals between Mars and Jupiter did not accrete into a planet. Jupiter’s gravity, through influence of orbital resonances, stirred up asteroid orbits and prevented their accretion into a planet.

55. Origin of Meteorites Most meteorites are pieces of _________.

56. Meteor Terminology _________: A rock from space that falls through Earth’s atmosphere. ______: The bright trail left by a meteoroid. _________: The rock that hits the ground.

57. Meteorite Types 1._________: Unchanged in composition since they first formed 4.6 billion years ago 2._________: Younger, have experienced processes like volcanism or differentiation

58. Primitive Meteorites

59. Processed Meteorites

60. Meteorites from Moon and Mars A few meteorites arrive from the Moon and Mars Composition differs from the asteroid fragments A cheap (but slow) way to acquire moon rocks and Mars rocks

61. Comet Facts Formed beyond the frost line, comets are icy counterparts to asteroids. The nucleus of a comet is like a “dirty snowball.” Most comets do ___ have tails. Most comets remain perpetually frozen in the outer solar system. Only comets that enter the _____ solar system grow tails.

62. _______ of Comet A “dirty snowball” Source of material for comet’s tail

63. Anatomy of a Comet ____ is atmosphere that comes from heated nucleus. ______ tail is gas escaping from coma, pushed by solar wind. ____ tail is pushed by photons.

64. Growth of Tail

65. Origin of Earth’s Water Water may have come to Earth by way of icy planetesimals from the outer solar system.

66. Famous Comets Halley’s Comet –Edmund Halley –76 year period –Nucleus 15x8 km –Next appearance 2062 Hale Bopp –Alan Hale and Thomas Bopp –4200 year period –50-60 million mile tail –Orbital speed 98,000 mph at perihelion 250 mph at aphelion

67. Photograph made by the Giotto spacecraft of the nucleus of Halley's comet. The spacecraft was approximately 1000 kilometers (about 620 miles) from the nucleus— deep inside Halley's coma of gas—during the time this picture was made. (Copyright 1986, Max Planck Institute for Aeronomy; courtesy Harold Reitsema, Ball Aerospace.)

68. Comet Hale-Bopp

69. Shoemaker-Levy 9 –Collided with Jupiter –400 km nucleus –Broke into 21 pieces before impact (A-W) Frag A generated an energy equivalent to 225,000,000,000 tons of TNT –Crater ½ Earth’s diameter

70. Comets eject small particles that follow the comet around in its orbit and cause meteor showers when Earth crosses the comet’s orbit.

71. Meteors in a shower appear to emanate from the same area of sky because of Earth’s motion through space.

72. ______ belt: On orderly orbits from 30–100 AU in disk of solar system ____ cloud: On random orbits extending to about 50,000 AU Only a tiny number of comets enter the inner solar system; most stay far from the Sun.

73. How did they get there? Kuiper belt comets formed in the Kuiper belt: flat plane, aligned with the plane of planetary orbits, orbiting in the same direction as the planets. Oort cloud comets were once closer to the Sun, but they were kicked out there by gravitational interactions with jovian planets: spherical distribution, orbits in any direction.

74. Pluto and Eris Much smaller than other planets Icy, comet-like composition Pluto’s moon Charon is similar in size to Pluto

75. What is Pluto like? Its largest moon Charon is nearly as large as Pluto itself (probably made by a major impact). Pluto is very cold (40 K). Pluto has a thin nitrogen atmosphere that refreezes onto the surface as Pluto’s orbit takes it farther from the Sun.

76. HST’s view of Pluto and moons

77. Pluto’s Orbit Pluto’s orbit is tilted and significantly elliptical. Neptune orbits three times during the time Pluto orbits twice — resonance prevents a collision. OrbitsOrbits of Neptune and Pluto

78. Is Pluto a Planet? Much smaller than the eight major planets Not a gas giant like the outer planets Has an icy composition like a comet Has a very elliptical, inclined orbit Pluto has more in common with comets than with the eight major planets.

79. Is Pluto a Planet? In 2006, the International Astronomical Union decided to call Pluto and objects like it “dwarf planets.”

80. Discovering Large Iceballs In summer 2005, astronomers discovered Eris, an iceball even larger than Pluto. Eris even has a moon: Dysnomia.

81. Other Icy Bodies There are many icy objects like Pluto on elliptical, inclined orbits beyond Neptune. The largest ones are comparable in size to Earth’s Moon.

82. Kuiper Belt Objects These large, icy objects have orbits similar to the smaller objects in the Kuiper Belt that become short period comets. So are they very large comets or very small planets?

83. Other Kuiper Belt Objects Most have been discovered very recently so little is known about them. NASA’s New Horizons mission will study Pluto and a few other Kuiper Belt objects in a planned flyby.