Homework #5

1. Homework #5 • Due Monday, October 13, 6PM • Covers Chapters 8, 9, and 10 • Estimated time to complete: 50 minutes • Read chapters, review notes before starting Note: Some of you have incompletes on previous assignments because you skipped one or more questions – go back and complete for partial credit on the skipped problems

2. Rocky Planets versus Icy Moons • Rock melts at higher temperatures. • Only larger rocky planets have enough internal heat from radioactivity. • Ice melts at lower temperatures. • Tidal heating can melt internal ice, driving activity.

3. Which of the following is not an explanation for why icy moons can still have geological activity while small terrestrial planets do not? • A) Ice melts at a much lower temperature than rock • B) Icy moons can feel strong tidal forces from their host planet • C) Small terrestrial planets do not have enough internal heat to sustain geological activity. • D) Icy moons gained more initial heat from the solar nebula to keep them warm than terrestrial planets did.

4. Which of the following is not an explanation for why icy moons can still have geological activity while small terrestrial planets do not? A) Ice melts at a lower temperature than rock B) Icy moons can feel strong tidal forces from their host planet C) Small terrestrial planets do not have enough internal heat to sustain geological activity. D) Icy moons gained more initial heat form the solar nebula to keep them warm than terrestrial planets did. Outer part of solar nebula was colder, not hotter than inner parts

5. What are Saturn’s rings like? • made up of numerous, tiny individual particles grain to boulder-size (not a solid disk) – each particle can be thought of as a tiny “moonlet” of Saturn. • ring particles orbit around Saturn’s equator. • ring system is very thin.

6. Spacecraft View of Ring Gaps Rings only a few tens of meters thick – length of Gallalee Hall! Collisions keep ring system thin and orbits circular.

7. Spacecraft View of Ring Gaps Rings only a few tens of meters thick – length of Gallalee Hall! Collisions keep ring system thin and orbits circular.

8. Artist’s Conception of Rings Close-Up Composed of water ice(and some rock) chunks 10 meters in size and smaller

9. Gap Moons • Some small moons create gaps within rings. • Gravitational perturbations cause ripples in rings.

10. Shepherd Moons • A pair of small moons can force particles into a narrow ring.

11. Jovian Ring Systems • All four Jovian planets have ring systems in equatorial plane. • Others have smaller, darker ring particles than Saturn, sometimes made of dust.

12. Why do the Jovian planets have rings? • Originally, it was thought that Saturn’s rings were formed by a large moon shattering (a rare event). • Discovery of rings around all Jovian planets ruled out this scenario. • They formed from ongoing impacts on moons orbiting those planets depositing dust/ice into orbit.

13. How do we know? • Rings aren’t leftover from planet formation because the particles are too small to have survived for so long (would have been ground down to nothing after 4.5 billion years by collisions with micrometeorites). • There must be a continuous replacement of tiny particles. • The most likely source is impacts with Jovian moons, which are plentiful in Jovian systems.

14. 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  all boulders will be gone in a billion years and it will have a ring system like the other Jovians.

15. Which of the following is true about ring systems and Jovian planets? • A) The rings rotate as one solid body, like a record. • B) All Jovian planets have a ring system. • C) Ring systems are typically ~100 km thick. • D) They are composed of large ~10 km boulders of ice.

16. Which of the following is true about ring systems and Jovian planets? • A) The rings rotate as one solid body, like a record. • B) All Jovian planets have a ring system. • C) Ring systems are typically ~100 km thick. • D) They are composed of large ~10 km boulders of ice. • Ring systems are only a few tens of meters thick (length of Gallalee Hall)

17. Chapter 8 Summary • Jupiter & Saturn – mostly H/He, Uranus/Neptune – mostly hydrogen compounds, all contain some rock/metal • Jovians became large (compared to terrestrials) because their cores could collect ice in addition to rock/metal • All Jovians have ice/rock/metal cores of ~5-10 Earth masses. Jupiter/Saturn also accreted a lot more H/He because they formed first in denser part of solar nebula • Jupiter is denser than its H/He composition implies, because its outer layers compressed the inner layers • Cloud layers on Jupiter (and to lesser extent Saturn) due to reflection off different molecules (NH3, H2O, NH4SH)

18. Chapter 8 Summary 6) Uranus & Neptune are blue-green because of high concentrations of methane in their atmosphere 7) All jovians have strong storms and strong magnetic fields 8) Small moons  no geological history, odd shapes orbits  probably all captured comets 9) Medium moons  past geological activity – big enough for self-gravity to make them spherical in shape 10) Large moons  ongoing geological activity, driven by (1) tidal forces (tidal heating) from host planet and (2) ice melts at much lower temperatures than rock

19. Chapter 8 Summary 11) Io (Jupiter moon) – most geologically active object in Solar System 12) Europa (Jupiter moon) – liquid water ocean 13) Titan (Saturn moon) – thick atmosphere, liquid methane lakes 14) Saturn’s rings – consist of countless small bits of ice, not solid rings, ring system as thin as length of Gallalee Hall 15) All Jovians have ring systems – small particles must be constantly replenished from impacts on moons

20. Exam #2 Approaching 2nd Exam will be a week from today (Tuesday, October 14) Covers chapters 6, 7, 8, 9, and 10 40 questions, multiple choice, no calculators needed Bring a #2 pencil and an eraser. Many questions will be similar to clicker questions and homework problems (but NOT identical).

21. Chapter 9Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

22. Asteroid Facts • Asteroids are rocky/metal leftovers of planet formation – not a shattered planet. • The largest is Ceres, diameter ~1000 kilometers. • >500,000 in catalogs, and probably over a million with diameter >1 kilometer. • Small asteroids are more common than large asteroids. • All the asteroids in the solar system wouldn’t add up to an object the size of our Moon.

23. The Slow Search for Asteroids • (1) Ceres discovered in January 1, 1801 (d= 2.77 AU) • (5) Astraea discovered in 1845 • By 1980, ~9000 discovered • By 1990, ~15,000 discovered • By 2000, ~100,000 discovered • By 2010, >500,000 discovered Brightest: Vesta (m=5.1) • Largest: Ceres (487 km radius)

24. The Slow Search for Asteroids Red: Earth-crossing asteroids Yellow: Closest approach to Sun is 1.3 AU Green: All others Asteroids flash white upon discovery, then fade for rest of video.

25. More Hollywood Nonsense Asteroid belt often depicted as a densely-packed, hazardous area for space pilots. In reality, asteroids are separated by millions of kilometers  like individual grains of sand separated by kilometers.

26. Asteroid Names (17058) Rocknroll (19383) Rolling Stones (8749) Beatles (246247) Sheldoncooper (214476) Stephencolbert (116939) Jonstewart (178008) Picard (2309) Mr. Spock* (2369) Chekhov (4659) Roddenberry *named after discoverer’s cat (pet names no longer accepted by International Astronomical Union) (3959) Irwin (32570) Peruindiana (1996) Adams (719) Albert (2383) Bradley (1643) Brown (2751) Campbell (8452) Clay (5635) Cole (1476) Cox (3638) Davis (1829) Dawson (9022) Drake (10774) Eisenach (2742) Gibson (2527) Gregory (19079) Hernandez (2220) Hicks (14466) Hodge (2193) Jackson (6461) Adam (54) Alexandra (291) Alice (227962) Aramis (5947) Bonnie (9974) Brody (3306) Byron (2980) Cameron (24484) Chester (192158) Christian (8452) Clay (2589) Daniel (1829) Dawson (4954) Eric (2167) Erin (4735) Gary (1516) Henry (19955) Holly (5938) Keller (22312) Kelly (14583) Lester (16142) Leung (10404) McCall (9460) McGlynn (3819) Robinson (876) Scott (22294) Simmons (3351) Smith (2603) Taylor (2555) Thomas (5500) Twilley (6372) Walker (21903) Wallace (4908) Ward (2335) James (3754) Kathleen (23739) Kevin (6824) Mallory (2779) Mary (448) Natalie (1343) Nicole (21936) Ryan (3147) Samantha (542) Susanna (2603) Taylor (2555) Thomas

27. Asteroids are cratered and not round  not enough mass for gravity to shape rock into a sphere.Only Ceres is large enough to be spherical  only dwarf planet in asteroid belt Eros as viewed from NEAR spacecraft

28. Asteroids with Moons • Some large asteroids have their own moon. • Asteroid (243) Ida has a tiny moon named Dactyl.

29. Density of Asteroids • Measuring the orbit of asteroid’s moon tells us an asteroid’s mass (about a dozen so far) - use Kepler’s laws. • Mass and size tell us an asteroid’s density. • Some asteroids are solid rock; others are just piles of rubble.

30. 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.

31. Why are asteroids rocky or metallic? • They originate from a large rocky terrestrial planet that was shattered early in the history of the Solar System. B) There was no ice in the part of the Solar System where they formed. C) Actually, asteroids are mostly made of ice. D) Because asteroids are escaped moons from the terrestrial planets

32. Why are asteroids rocky or metallic? • They originate from a large rocky terrestrial planet that was shattered early in the history of the Solar System. B) There was no ice in the part of the Solar System where they formed. C) Actually, asteroids are mostly made of ice. D) Because asteroids are escaped moons from the terrestrial planets Asteroids formed inside the frost line  no ice available

33. Landing on an Asteroid Japanese lander Hayabusa landed on (25143) Itokawa on November 19, 2005, but failed to collect rock samples.

34. Landing on an Asteroid Still, dust was collected in its collecting horn, and Hayabusa returned to Earth in June 2010.

35. Meteor Terminology • Meteoroid: a sand- to boulder-size piece of asteroid floating through interplanetary space in Earth’s vicinity • Meteor: the bright trail in the sky left by a meteoroid (also called a “shooting star”) as it burns up in the atmosphere • Meteorite: a rock from space that falls through Earth’s atmosphere and lands • Quote from Thomas Jefferson: “It is easier to believe that Yankee professors would lie than that stones would fall from heaven.”

36. Meteorite Impact Meteorite 1, Chevy Malibu 0 Chicago, March 26, 2003 Peeksgill, NY Oct. 9, 1992

37. Meteorite Impact Novato, California October 18, 2012

38. Has a human ever been hit by a meteorite? A) No, a human has never been hit. B) Yes, a human has been hit once, but not killed. C) Yes, a human has been hit once and killed. D) People are hit about once every 10 years by a meteorite. 4 points for all who answer

39. Has a human ever been hit by a meteorite? A) No, a human has never been hit. B) Yes, a human has been hit once, but not killed. C) Yes, a human has been hit once and killed. D) People are hit about once every 10 years by a meteorite. 4 points for all who answer

40. Stars Meteorites Fell On Alabama Ann Hodges of Sylacauga, Alabama was hit and injured by a 8.5 lb meteorite on November 30, 1954 as she napped in her chair. Meteorite now resides down the street in the Natural History Museum.

41. Meteorite Types 1) Primitive (chondrites): unchanged in composition since they first formed 4.6 billion years ago in the solar nebula; - stony-iron (inner asteroid belt) - carbon-rich (outer asteroid belt) 2) Processed: slightly younger (by a few hundred million years); have experienced processes like volcanism or differentiation - metal-rich (cores of asteroids) - rocky (crusts of asteroids)

42. Primitive Meteorites Stone, metal mixed together  no differentiation

43. Processed Meteorites Underwent differentiation or volcanic processes

44. Meteorites from Moon and Mars • A few meteorites arrive from the Moon and Mars via large impacts. • Composition differs from the asteroid fragments. • A cheap (but slow) way to acquire Moon rocks and Mars rocks Martian meteorites Discovered July 2011

45. What are comets like? Comet Hyakutake - 1996

46. Comet (Greek for “hair”) Facts • Formed beyond the frost line, comets are icy counterparts to asteroids. • Nucleus of comet is a “dirty snowball.” • Most comets do not have tails. • Most comets remain perpetually frozen in the outer solar system. • Only comets that enter the inner solar system grow tails.  key point • Comets are icy analogs of asteroids.

47. Nucleus of Comet • A “dirty snowball” composed of rocky dust and icy (~20 km) • Hydrogen compounds also found, also CO  very cold • Contain complex organic compounds (e.g., amino acid glycine)  life origins? • Source of material for comet’s tail Comet Wild 2 as viewed from Stardust spacecraft in 2004

48. Deep Impact • Mission to study nucleus of Comet Tempel 1 • Projectile hit surface on July 4, 2005. • Many telescopes studied aftermath of impact.

49. Anatomy of a Comet • A coma is the atmosphere that comes from a comet’s heated nucleus. • A plasma tailis gas escaping from coma, pushed by the solar wind (protons and electrons) • A dust tailis pushed by photons (light) • Tails can be hundreds of millions of km long (i.e. more than 1 AU) Comet Hale-Bopp Halley’s Comet

50. Growth of Tail Tails always point away from Sun. Comets lose ~0.1% of their ice on each passage around Sun. Dust debris left behind near Earth’s orbit lead to annual meteor showers.