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Homework 6

Homework 6. Due Thursday, November 15. Quiz #3. End of class on Tuesday, November 20 Similar in nature to Quiz #1 and #2 (no formula sheet, no calculators) Covers material since Exam #2. Press Release Talk. Thursday, November 15: Connor and John will talk about:

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Homework 6

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  1. Homework 6 Due Thursday, November 15

  2. Quiz #3 End of class on Tuesday, November 20 Similar in nature to Quiz #1 and #2 (no formula sheet, no calculators) Covers material since Exam #2

  3. Press Release Talk Thursday, November 15: Connor and John will talk about: “BepiColombo Launches on Long Journey to Mercury” https://www.nytimes.com/2018/10/19/science/bepicolombo-mercury-launch.html

  4. Press Release Talk Thursday, November 15: Blake and Oleksandr will talk about: “What's keeping us from discovering dark matter?” http://www.astronomy.com/news/2018/10/whats-keeping-us-from-discovering-dark-matter

  5. Medium Moons of Uranus • They have varying amounts of geological activity. • Miranda has large tectonic features and few craters (possibly indicating an episode of tidal heating in past).

  6. Neptune’s Moon Triton • Similar to Pluto, but larger, and orbits backwards • Evidence of past geological activity (tidal heating?)

  7. Why are small icy moons more geologically active than small rocky planets?

  8. Rocky Planets versus Icy Moons • Rock melts at higher temperatures. • Only large rocky planets have enough heat from radioactivity. • Ice melts at lower temperatures. • Tidal heating can melt internal ice, driving activity. But do we really understand heating?

  9. What are Saturn’s rings like? • made up of numerous, tiny individual particles grain to boulder-size. • orbit around Saturn’s equator. • are very thin.

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

  11. Artist’s Conception of Rings Close-Up Composed of water ice

  12. 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.

  13. Why do the Jovian planets have rings? • Originally, it was thought that the only way to form a ring was by a moon shattering (a rare event). • Discovery of rings around all Jovian planets ruled out this scenario. • They formed from dust created in impacts on moons orbiting those planets.

  14. 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 moons. • Large boulders could originate from occasional shattering of a small moon

  15. 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 gone in a billion years.

  16. Chapter 12Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

  17. Asteroid Facts • Asteroids are rocky/metal leftovers of planet formation. • The largest is Ceres, diameter ~1000 kilometers. • ~600,000 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 (NOT a shattered planet).

  18. First Searches for Asteroids • Search motivated to find “missing” planet at 2.8 AU from Sun in late 18th century • Titius-Bode Law: Numerical sequence approximating distance of planets from Sun: a = 0.4 + 0.3 * 2m AU, m = -∞, 0, 1, 2, 3, 4, …… m=-∞, a = 0.4, Mercury: 0.39 AU m=0, a = 0.7, Venus: 0.72 AU m=6, a = 19.6, Uranus: 19.2 AU m=1, a = 1.0, Earth: 1.00 AU m=7, a = 38.8, Neptune: 30.1 AU m=2, a = 1.6, Mars: 1.52 m=3, a = 2.8, asteroid belt? (Ceres at 2.77 AU) m=4, a = 5.2, Jupiter: 5.20 AU m=5, a = 10.0, Saturn: 9.54 AU

  19. 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 2015, >~700,000 discovered Brightest: Vesta (m=5.1) • Largest: Ceres (487 km radius)

  20. Asteroid Names (17058) Rocknroll (19383) Rolling Stones (8749) Beatles (246247) Sheldoncooper (391257) Wilwheaton (214476) Stephencolbert (116939) Jonstewart (178008) Picard (2309) Mr. Spock* (2369) Chekhov (3594) Scotti *named after discoverer’s cat (pet names no longer accepted by International Astronomical Union) (8452) Clay (9164) Colbert (5835) Cole (3032) Evans (12292) Dalton (16238) Fox (2589) Daniel (2335) James (28475) Garrett (12777) Manuel (113333) Tyler (1574) Meyer (12130) Mousa (22622) Strong (3959) Irwin (32570) Peruindiana (165347) Philplait More at http://www.minorplanetcenter.net/iau/lists/MPNames.html

  21. Asteroid Orbits • Most asteroids orbit in the asteroid beltbetween Mars and Jupiter. • Orbits of near-Earth asteroids cross Earth’s orbit. • Trojan asteroids follow Jupiter’s orbit by +/- 60° (L4 and L5 Lagrangian points).

  22. 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.

  23. 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 grains of sand separated by kilometers.

  24. 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

  25. How Do We Estimate Sizes of Asteroids? In general, asteroids are NOT spatially resolved from Earth.Optical light  tells us how much sunlight it reflects.Infrared light  tells us how much thermal (blackbody) radiation it is emitting.Relative ratios gives us albedo and rough size.

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

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

  28. Meteor Terminology • Meteoroid: a sand- to boulder-size piece of asteroid or comet (or planet)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 • Supposed quote from Thomas Jefferson: “It is easier to believe that two Yankee professors would lie than that stones would fall from heaven.”

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

  30. Meteorite Impact Novato, California October 18, 2012

  31. 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.

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