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

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