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Minor Bits of the Solar System

Minor Bits of the Solar System. Asteroids, Comets and Meteoroids & Extrasolar Planets too!. Nucleus of Comet Wild2. ASTEROIDS: aka, Minor Planets. Smaller than planets, but many similarities

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Minor Bits of the Solar System

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  1. Minor Bits of the Solar System Asteroids, Comets and Meteoroids & Extrasolar Planets too! Nucleus of CometWild2

  2. ASTEROIDS: aka, Minor Planets • Smaller than planets, but many similarities • Over 75,000 cataloged; over 200,000 down to 100 m “known”; lots discovered by Sloan Digital Sky Survey • Most are probably solid; irregular shape • Some are “rubble piles”, easily disrupted • Gaspra (S type) and Ida (S type, w/ “moon” Dactyl)

  3. Asteroid Orbits • Most in ASTEROID BELT: 2.1 AU < a < 3.3 AU • Kirkwood gaps: PA = 1/2, 1/3, 1/4, 2/5, 3/7 PJ --- Jupiter prevented growth of a planet in the belt • Amor: Mars-crossing;Trojan: near Jupiter's L4 and L5 • Apollo: Earth-crossing, can  big craters & destruction

  4. Kirkwood Gaps: Resonances with Jupiter

  5. Last Pop Quiz • Person at the right of each row, take out a piece of paper • Neatly print your name on it. • Pass it to your left. • If you’re here, 10 pt, if not, 0.

  6. Answers to Review Questions • T: Venus’s atm conducts heat rapidly • F: Valles Marinaris & Olympus Mons (but it’s inactive) • F: MJ = 318 ME but > 2 times all others! • F: Saturn rotates almost as fast as Jupiter and has differential rotation too • F: only after Uranus’s orbit wasn’t explained by known planets’ gravity was Neptune predicted, searched for & found • T: 1:2:4 periods for Io, Europa & Ganymede heat Io & Europa a lot via elliptical orbits & induced strong tides • T: Saturn has 61 known moons, but only Titan is big • F: ion tails point away from Sun

  7. Rest of Answers • 9) A -- iron rust gives Mars its red color • 10) E -- densities between 1.3 and 2 g/cm3 : ice+rock • 11) C -- 1/D = 1/R - 1/P here R=2.00 d, P = 8.00 d so 1/D = 1/2 - 1/8 = 3/8 and D = 8/3 d = 2.67 d • 12) C -- rocky core, liquid metallic H2, liquid & gas H2 • 13) C -- 4 km/s and eventually escapes Vth=(3kT/mmole)1/2 (and Vesc = (2GM/R)1/2 ) Vth(H2)/Vth(O2) = (mO/mH)1/2 = (32/2)1/2 = 4 and as Vth(O2) = 1 km/s, Vth(H2) = 4 km/s • Since Vth(H2) > (1/6) Vesc = 2 km/s the H2 will eventually escape

  8. Asteroid Classes and Physical Properties • C-type (Carbonaceous): majority, darkest, dominate farther out,   1.3 g/cm3, porous? • S-type (silicate) reflect more light, more in inner belt,   2.0 g/cm3 • Biggest in the Asteroid Belt: Ceres (D = 940 km), Pallas (580 km), Vesta (540 km)--probably had volcanoes • Some are binary: from Earth --- Pallas, from Space (Galileo) --- Ida (& Dactyl); frequent collisions  moons • New are Quaoar: past Pluto at 42 AU, (D = 1300 km), the 3rd biggest Plutino -- very icy so really more like comets • Sedna: very eccentric, a  480 AU, D  1800 km -- currently at 75 AU, most distant Kuiper belt object known

  9. Space Mission to Asteroids Near Earth Asteroid Rendezvous: NEAR • Took close-up photos of Mathilde (C-type; about 60x50 km) in 1997 • Orbited and crash-landed into Eros (S-type;34x11x11km) in 2001. Inset: “young” area where rubble filled in craters

  10. Danger from Space!!! • When earth crossing asteroids hit the earth, the energy of the impact can be huge; speeds ~ 20 km/s • Even modest (100 m size) meteoroids can produce big craters (every 200,000 yr or so) • Extinctions from massive amounts of debris kicked into the atmosphere, blocking sunlight for years and killing plants (every 70,000,000 yrs or so) -- last one @ Cretaceous/Tertiary boundary 66,000,000 yr ago Manicouagan reservoir in Quebec: 70 km in diameter: hit by meteoroid ~2x108 yr ago

  11. COMETS: Dirty Ice-balls Seen as bright trails across the sky COMPONENTS: • NUCLEUS --- typically 10 km across When warm enough the ice SUBLIMATES • COMA --- gases sublimated from nucleus • HYDROGEN ENVELOPE --- 106 km • IONIZED TAIL --- pushed directly away from the Sun, by the SOLAR WIND; up to an AU • DUST TAIL --- curved, due to inertia of heavier dust particles wanting to follow orbit

  12. Cometary Structure (Halley)

  13. Anatomy of a Comet Movie

  14. Cometary Tails • Halley (last slide) • Giacobini-Zinner (1959); ion tail over 5x105 km • Hale-Bopp (1997) showed both ion and dust tails, streching over 40O

  15. COMETARYORBITS • Very elliptical orbits, many highly inclined • Usually FROZEN; warm up near 5 AU • Most nuclei in OORT CLOUD: 10,000 -- 50,000 AU; originated closer, ejected by jovian planets long ago • “Short” period comets: KUIPER BELT --- formed outside Neptune: over 1000 known, so over 100,000 > 100 km • Many molecules found in their spectra: CH4, NH3, CO2 & H2O

  16. Tail Directions and Density • Tails basically point away from the Sun, but dust tails form later and are more curved • As the comet recedes from Sun, its tail is in front of it! • VERY POROUS w/  ~ 0.1 g/cm3

  17. Comet Deep-Freezers:The Oort Cloud and Kuiper Belt

  18. Pluto: King of the Kuiper Belt Objects • Pluto isn’t much bigger than several other KBOs, especially Sedna, probably about the same size and Eris, which is probably somewhat bigger. • So Pluto should be called a Minor Planet (aka asteroid or KBO) not a (Major) Planet

  19. Kuiper Belt Objects & Pluto • Eris, Pluto & other big KBOs • Pluto has 4 moons: Charon, Nix & Hydra • Surface in “true” color: made during eclipses of Pluto by Charon (and vice versa)

  20. FAMOUS COMETS: Halley’s • In 1705 Edmund Halley recognized several historical apparitions as recurrent: 76 year period; calculated orbit • Predicted its return in 1758 --- confirmed Newton's Laws • As seen in 1910 (spectacular) and 1986 (much less so) • Vega 2 & Giotto flew by & came very close in 1986: showed it to be irregular (15 by 10 km), very dark, with jets streaming from cracked outer layers

  21. Halley’s Comet’s Nucleus Resolved • Picture taken by ESA’s Giotto -- 50 m resolution. Brightest jets from gas and dust from nucleus

  22. Hale-Bopp Nucleus Animation

  23. FAMOUS COMETS: Shoemaker-Levy 9 • Discovered in 1993 while heading for Jupiter • Tides shredded and trapped it • Hit atmosphere in July 1994; big splashes above clouds • Effects in atm seen for months

  24. Deep Impact Mission • Collision w/ Comet Tempel 1 on July 4 2005 • Impactor gouged out a large hole while main satellite used photography and spectroscopy to probe composition

  25. METEOROIDS, METEORS, & METEORITES METEOROID: ANY DEBRIS < 100 m SIZE METEORS or Shooting Stars • Bright flashes in our atmosphere • Most: completely destroyed dust or pebbles • Rocks are brighter, some survive to become METEORITES

  26. METEOR SHOWERS: many more than usual • bigger dust lost by a comet left in the same orbit for many years; comets eventually are worn out • when Earth crosses the tail, they appear to RADIATE from a constellation • Perseid on Aug 11, 50/hr (Swift-Tuttle) • Draconid on Oct 9, 500/hr (Giacobini-Zimmer) • Leonid on Nov 16, 10/hr (up to 1000/min) (Tuttle) • Brightest meteors from big independent Meteoroids

  27. METEORITES: Messengers from Space Main CLASSES • STONY (93% of FALLS) --Most are S-type, basically rocky w/o chondrules, or achondritic -- these are the mostcommon type toland. --Many are Carbonaceous --Rare & primitive: CARBONACEOUS CHONDRITES • STONY-IRON • IRON-- very rare, but easily recognized; so most commonlyfound type. • All have densities more like asteroids than comets

  28. Big Meteorites Ahnighito, about 34 tons; Wabar, about 2 tons

  29. Meteorite Types • Stony (silicate) showing a dark crust from melting during passage through atmosphere • Iron showing crystalline structure on polished and etched surface

  30. Origins of Meteorites • Many left from Solar System formation: 4.55 Gyr old • Primitive: mainly stony which condensed in inner SS and carbon rich ones that formed in outer asteroid belt) • Asteroid fragments --- show evidence of heating • Processed: from differentiated objects, some like lava flows, so from the surface; others metallic, so from the cores of smashed asteroids • Blasted off the Moon --- many inclusions (rare) • Ejected from Mars --- different abundances of trapped gases (really rare)

  31. PLANETS AROUND OTHER STARS? • First evidence: DUST DISKS around nearby young stars. • Such disks often had holes in the center: likely to be areas cleared out by planets. • Spitzer ST of Fomalhut dust disk; Hubble ST of HR 4796A

  32. Resonably Direct Evidence • Only since 1994 (51 Pegasi) • Very accurate RADIAL VELOCITIES (50 m/s) of stars indicate tugs from much less massive objects with periods of days to years.

  33. Doppler shifts show Extrasolar planets around 51 Pegasi & Upsilon Andromedae (3) • SECOND WAY: Very precise ASTROMETRY (0.002 arcsec) could indicate wobbles in stars' paths over years which are also due to companions

  34. Statistics of Extrasolar Planets As of 2009, > 400 good indirect planet detections Dozens of stars have multiple planets detected • Both techniques: Much easier to detect close, multi-Jupiter mass planets,so, most found are more massive than Jupiter but a few ~ Neptune have been estimated

  35. Surprise: Hot Jupiters within 1 AU! Formed in situ; survive heat and wind? • Migrated inward through nebular disk? • Are these the typical planetary systems or just a selection effect? IS OUR SOLAR SYSTEM WEIRD? • A few planets transits have been seen after orbit known from radial velocity curves, confirming them for sure!

  36. Other Searches for Extrasolar Planets Direct evidence preferred: we want an IMAGE! • Imaging via blocking out light of star: coronagraph (IR much better than visible since ratio less extreme) • Finally done in 2009 • Interferometry could separate very nearby points: Space Interferometry Mission being planned (~2012) • Next stage: Earths, not just Jupiters: • Kepler mission currently looking for transits (2009); found 1 • Giving info on atmospheres of jovian exoplanets • Search for Extra Terrestrial Intelligence (SETI): • How?: radio signals, optical (laser) signals, visits??? • See Astronomy 1020 (Chapter 28)

  37. Congratulations! • You’ve survived (well, only one exam’s left) Astronomy 1010.

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