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Defending Planet Earth

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2011 American Astronautical Society Robert H. Goddard Memorial Symposium--Mike A'Hearn, University of Maryland

2011 American Astronautical Society Robert H. Goddard Memorial Symposium--Mike A'Hearn, University of Maryland

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  • 1. Defending Planet Earth
    Mike A’Hearn
  • 2. Chixculub
    31-3-11
    Goddard Symposium
    mfa - 2
    Every 50-100 Myears
  • 3. Tunguska
    31-3-11
    Goddard Symposium
    mfa - 3
    Airburst of oblique impactor
    5-30 Mtons of TNT (20-130 Pj) 30-100m diameter impactor Everything flattened over >2000 km2 Possibly one every 200 years
    1927 vs. 2008
  • 4. Size Distribution & Frequency
    31-3-11
    Goddard Symposium
    mfa - 4
  • 5. Finding Them
    From Space vs. from Earth
    Earth-trailing orbit is fastest
    From Earth’s surface is cheapest
    IR vs. Visible
    IF! In space, IR seems better
    Goal of G. E. Brown survey
    90% of >140m
    31-3-11
    Goddard Symposium
    mfa - 5
  • 6. Kill Curves
    31-3-11
    Goddard Symposium
    mfa - 6
  • 7. Annual Deaths
    31-3-11
    Goddard Symposium
    mfa - 7
    LP Comets ignored ~10%, notimportant
    LP Comets ignored ~50% Whoops!
  • 8. Mitigation (per NRC)
    4 approaches depending on circumstances
    Civil defense (evacuation, sheltering, first aid, etc.
    Up to 50m diameter?
    Slow Push-Pull (tug, solar heating, albedo change, gravity tractor, et al.)
    Needs decades to operate (plus time to build, etc.)
    Max size 300-600 m diameter
    Gravity tractor closest to ready and least dependent on properties of NEO
    Kinetic Impacts (Super Deep Impact)
    sensitive to porosity of top meters to tens of meters
    momentum transfer efficiency not known
    much wider range of applicability (max size 1 to 1.5 km, shorter warning for small ones)
    Nuclear blast
    standoff blast best
    works up to 10 km and relatively short warning
    31-3-11
    Goddard Symposium
    mfa - 8
  • 9. Mitigation Applicability
    31-3-11
    Goddard Symposium
    mfa - 9
  • 10. What Next?
    Don Quixote-like mission
    a rendezvous spacecraft at a small NEO followed by a large impactor
    biggest gain in knowledge directly related to mitigation
    Guess $1.5G; Good for international collaboration
    Gravity tractor demonstration
    fewer unknowns other than engineering
    second priority
    Apophis a possible target but any small NEO will do
    Can’t predict which might need to be used first
    Small NEO is by far the most likely
    Warning time very uncertain but short warnings are likely at ~100m diameter or less
    31-3-11
    Goddard Symposium
    mfa - 10
  • 11. Research Needs
    Momentum transfer
    Warning times
    Tails of orbital distribution
    NEO properties - spin & shape, multiplicity, & especially porosity and density
    lots for science but not so much for hazard mitigation
    hence radar programs at Arecibo and Goldstone
    Physics of airbursts
    search strategy - death plunge vs. full survey
    Effects of the wide range of NEO properties on the mitigation strategy
    tsunami generation
    NEO disruption
    31-3-11
    Goddard Symposium
    mfa - 11
  • 12. Incomplete Mitigation
    31-3-11
    Goddard Symposium
    mfa - 12
    Risk of incomplete mitigation could lead to paranoia or even retaliation
    Risk of retaliation could lead to total inaction
    Requires official, working level close cooperation
  • 13. Bottom Line
    Insurance prevents destruction rather than compensating to rebuild
    How much insurance do we want?
    31-3-11
    Goddard Symposium
    mfa - 13
  • 14. Backup Slides