Minor Bits of the Solar System

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Minor Bits of the Solar System

• Asteroids, Comets and Meteoroids Extrasolar
  Planets too!

Nucleus of Comet Wild2
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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)

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Asteroid Orbits

• Most in ASTEROID BELT 2.1 AU lt a lt 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

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Kirkwood Gaps Resonances with Jupiter
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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 youre here, 10 pt, if not, 0.

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Answers to Review Questions

• T Venuss atm conducts heat rapidly
• F Valles Marinaris Olympus Mons (but its
  inactive)
• F MJ 318 ME but gt 2 times all others!
• F Saturn rotates almost as fast as Jupiter and
  has differential rotation too
• F only after Uranuss orbit wasnt explained by
  known planets gravity was Neptune predicted,
  searched for found
• T 124 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

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Rest of Answers

• 9) A -- iron rust gives Mars its red color
• 10) E -- densities between 1.3 and 2 g/cm3
  icerock
• 11) C -- 1/D 1/R - 1/P here R2.00 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) gt (1/6) Vesc 2 km/s the H2 will
  eventually escape

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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

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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-type34x11x11km) in 2001. Inset young area
  where rubble filled in craters

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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 _at_ Cretaceous/Tertiary boundary
  66,000,000 yr ago

Manicouagan reservoir in Quebec 70 km in
diameter hit by meteoroid 2x108 yr ago
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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

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Cometary Structure (Halley)
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Anatomy of a Comet Movie
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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

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COMETARY ORBITS

• 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
  gt 100 km
• Many molecules found in their spectra CH4, NH3,
  CO2 H2O

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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

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Comet Deep-FreezersThe Oort Cloud and Kuiper
Belt
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Pluto King of the Kuiper Belt Objects

• Pluto isnt 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

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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)

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FAMOUS COMETS Halleys

• 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

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Halleys Comets Nucleus Resolved

• Picture taken by ESAs Giotto -- 50 m resolution.
  Brightest jets from gas and dust from nucleus

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Hale-Bopp Nucleus Animation
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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

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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

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METEOROIDS, METEORS, METEORITES

• METEOROID ANY DEBRIS lt 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

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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

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METEORITES Messengers from Space

• Main CLASSES
• STONY (93 of FALLS)
  --Most are S-type, basically
  rocky w/o chondrules, or achondritic -- these are
  the most common type to land.
  
  --Many are Carbonaceous
  --Rare primitive
  CARBONACEOUS CHONDRITES
• STONY-IRON
• IRON -- very rare, but easily recognized so most
  commonly found type.
• All have densities more like asteroids than
  comets

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Big Meteorites
Ahnighito, about 34 tons Wabar, about 2 tons
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Meteorite Types

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

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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)

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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

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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.

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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

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Statistics of Extrasolar Planets

• As of 2009, gt 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

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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!

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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)

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Congratulations!

• Youve survived (well, only one exams left)
  Astronomy 1010.