SPACE DEBRIS: ASTEROIDS, COMETS,
METEOROIDS and METEORS

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ASTEROIDS --- Minor Planets

  • Smaller than planets, but many similarities
  • Over 75,000 cataloged; over 200,000 down to 100 m known
  • Most are probably solid; irregular shape
  • Some are ``rubble piles'', easily disrupted

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    ORBITS

  • Largest number in ASTEROID BELT
  • Between 2.1 and 3.3 AU
  • Kirkwood gaps: P_A = 1/2, 1/3, 1/4, 2/5, 3/7 P_J
    --- Jupiter prevented growth
  • Amor: are Mars-crossing
  • Apollo: Earth-crossing, can --- > big craters
  • Trojan: are near Jupiter's L_4 and L_5

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    CLASSES

  • C-type (Carbonaceous) are majority, darkest, dominate farther out,
    density about 1.3 g/cm^3, porous?
  • S-type (silicate) reflect more light, more in inner belt,
    densities about 2 g/cm^3

  • Biggest: Ceres (D = 940 km), Pallas (580), Vesta (540)
  • New is Quaoar: past Pluto (at 42 AU), (D = 1300 km)
  • Newer is Sedna: now at 75 AU, but a ~= 480 AU; extremely eceentric orbit;
    most distant known Kuiper Belt Object, D ~= 1800 km, so similar in size to Mercury

    Some are binary: from Earth --- Pallas, from Space (Galileo) --- Ida (& Dactyl)

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    Near Earth Asteroid Rendezvous --- NEAR

  • Took close-up photos of Mathilde (C-type) in 1997
  • Orbited and crash-landed into Eros (S-type) in 2001.

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    COMETS --- Dirty Ice-balls

    COMPONENTS

  • Seen as bright trails across the sky
  • NUCLEUS --- typically 10 km across
  • When warm enough the ice SUBLIMATES
  • COMA --- gases sublimated from nucleus
  • HYDROGEN ENVELOPE --- 10^6 km
  • IONIZED TAIL --- pushed directly away from the Sun,
    by the SOLAR WIND; up to an AU
  • DUST TAIL --- curved, due to inertia

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    ORBITS

  • Very elliptical orbits, many highly inclined
  • Usually FROZEN; warm up near 5 AU
  • Most nuclei in OORT CLOUD: 10,000 -- 50,000 AU
  • Short period comets: KUIPER BELT --- outside Neptune

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    SOME FAMOUS COMETS

    Halley's Comet

  • Apparitions recognized as recurrent: 76 year period
  • Predicted to show in 1758 --- confirmed Newton's Laws
  • Vega 2, Giotto flew came very close in 1986 and showed it to be
    irregular (15 by 10 km), very dark, with jets streaming
    from cracked outer layers

    Comet Shoemaker-Levy 9

  • Discovered in 1993 -- heading for Jupiter
  • Tides shredded and trapped it
  • Hit atmosphere in July 1994; left big splashes above the clouds
  • Effects seen for months; dust still settling

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    METEOROIDS, METEORS, METEORITES

    METEORS or Shooting Stars

  • Bright flashes in our atmosphere
  • Most: completely destroyed dust or pebbles
  • Rocks are brighter, some survive

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    METEOR SHOWERS: many more than usual

  • bigger dust lost by a comet
  • left in the same orbit for many years
  • 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, typically 10/hr (but up to 1000/min !) (Tuttle)

    The BRIGHTEST METEORS are from large, independent METEOROIDS --
    fragments of asteroids

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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.

    ORIGINS

  • From Solar System formation: 4.55 Gyr
  • Asteroid fragments --- evidence of heating
  • Blasted off the Moon --- many inclusions
  • Ejected from Mars --- different abundances of trapped gases