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Comets and Asteroids

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Nucleus seems to be composed of several fragments. ... One thing 'Armageddon' got right ' ... for 'Armageddon': $34.8 million. The Threat is Real. In any year... – PowerPoint PPT presentation

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Title: Comets and Asteroids


1
Comets and Asteroids
  • Paul J. Thomas
  • Department of Physics and Astronomy
  • University of Wisconsin - Eau Claire

2
Asteroids
Ida and Dactyl, from the Galileo spacecraft
3
The Asteroid Belt
4
Comets
Comet Hale-Bopp
5
The Kuiper Belt and Oort Cloud
6
The Comet Nucleus
Halley
Tempel 1
7
Deep Impact Mission
8
Surprises from Comet Tempel 1
  • Nucleus seems to be composed of several
    fragments.
  • Water vapor vents appeared all over the nucleus,
    as expected, but carbon dioxide only vented from
    certain parts.
  • Dust only came from the carbon dioxide vents.

9
Surprises from Comet Tempel 1
  • There are some very smooth areas on the nucleus,
    as if something had flowed there. However, the
    comet's gravity is extremely weak.
  • There are circular areas with raised rims that
    resemble impact craters. But the surface gets
    vaporized every time the comet's orbit takes it
    close to the sun.

10
Organic Molecules in Comets and Asteroids
  • Carbonaceous chondrite asteroids are 3-5 organic
    by mass.
  • 3 of organic asteroidal carbon is amino acids.
  • Kerogen is similar to chondritic organics.
  • Halley dust is 30 organic by mass.
  • Halley gas is 14 organic by mass.

11
The Early Terrestrial Environment
  • Complex terrestrial organisms 3.5 Gya.
  • Probable biologically mediated C12/C13
    fractionation 3.8 Gya.
  • Heavy Bombardment ended 3.8 Gya.

12
Meteorites through the roof
Sylacauga, AL, 1954
Freehold Township, NJ, 2007
13
Comet Shoemaker-Levy 9
14
Asteroid 1997XF11
  • 2 km diameter asteroid.
  • Brian Marsden (Harvard) calculated 2028 close
    approach of 40,000?180,000 km!
  • Paul Chodas and Don Yeomans (JPL) revised this to
    80,000?2,500 km.
  • Still, it will almost certainly hit Earth
    eventually...

15
Podkammenaya Tunguska Area
  • 2200 km2 area of felled trees.
  • No central crater, but stand of trees stripped of
    bark and leaves.

16
The Tunguska Epicenter
17
Tunguska Blast Site
  • Butterfly pattern consistent with incidence
    angle of ?45º, airburst height of 10 km (Zotkin
    and Tsikulin, 1966 Korobeinikov et al., 1976)

18
Tunguska Then and Now
19
15 MT Airburst Models
20
Meteor Crater, Arizona
  • 50,000 years old.
  • 15 MT event.
  • Iron asteroid.

21
Airbursts
Tunguska, 1908
Once in 300 years
22
Crater Cluster on Venus
  • 25.6 latitude 336.0 longitude.
  • 1.5 km diameter.
  • Appears to have been formed by four fragments of
    a single object.

23
Small Terrestrial Impacts
Once in 10,000 years
Barringer Meteor Crater, 50,000 y
24
Large Terrestrial Impacts
Once in 100,000 years
Gosses Bluff, 143 My
25
Civilization-Ending Impacts
Vredefort, 1,970 My
Once in a million years
Manicouagan, 210 My
26
Extinction-Level Events
Once in a 100 million years
Chicxulub, 65 My
27
Near Earth Objects (NEOs)
  • Near Earth Asteroids (NEAs)
  • 5083 discovered so far
  • 730 with diameters gt 1 km
  • 900 Potentially Hazardous Asteroids (PHAs)
  • Comets
  • Much higher impact speeds, impossible to
    catalogue all objects

28
Spacewatch Telescopes
0.9 and 1.8 m telescopes discover 20 Near Earth
Asteroids/year
Spacewatch telescope, Kitt Peak, Arizona
1994 GK
1994 GL
1994 XM1
29
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32
One thing Armageddon got right
  • Mr. President, NASAs budget for hunting the sky
    for asteroids is only a million dollars a year
    and - excuse my language - its a real big-assed
    sky out there.
  • NASAs Executive Director, Dan Truman
  • (Billy Bob Thornton)
  • Opening weekend grosses
  • for Deep Impact 41.1 million
  • for Armageddon 34.8 million

33
The Threat is Real
  • In any year
  • Probability of 1/100,000 of Earth being hit,
    without warning, by an undiscovered NEO gt1 km in
    diameter.
  • Probability of 1/1,000 to 1/100 of Earth being
    hit, without warning, by an undiscovered NEO 60
    m in diameter.
  • These unknown NEOs currently pose a far greater
    risk than any known NEO.
  • Rick Binzel, Ted Bowell, Clark Chapman, Paul
    Chodas, Paolo Farinella, Al Harris,
    Andrea Milani, David Morrison, Steve Ostro, Don
    Yeomans
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