Clark R. Chapman

1. http://www.boulder.swri.edu/clark/clark.html NEO IMPACT SCENARIOS Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA, and “The B612 Foundation” Session 3-PD-3 “Threats & Consequences II” AIAA-2004-1416 2004 Planetary Defense Conference: Protecting Earth from Asteroids Garden Grove CA USA 23 February 2004

2. In the Post 9/11 World... What kinds of impact predictions do we really have to plan for? How does society respond to real (or imagined) threats? It’s more than engineering, folks!

3. Sizes, Impact Frequencies of NEOs Leonid meteor shower Smallest, most frequent Second Week Boulder Dust Peekskill meteorite Huge, extremely rare Building 15 km 100 Myr Tunguska, 1908 Millennium K-T mass extinctor, 65 Myr ago Mountain 500,000 yr SL9 hits Jupiter 1994

4. Asteroid Size Distribution:How Often Impacts of Different Energies Happen Courtesy Al Harris

5. Death Threat from Impacts, by Asteroid Diameter and Location of Impact • Statistical mortality from impacts, post-Spaceguard, distinguished by size and location of impact (NEO Science Definition Team [SDT], 2003) • SDT tsunami hazard is divided by 10 (think deaths, not property damage) • Land impacts by <100m asteroids (Tunguskas) are objectively important, but they also occur MUCH more frequently than Global destroyers • Tunguskas and their smaller cousins may dominate popular interest in the impact hazard, and hence the work of the NEO community. (For nominal case) Global Max Nominal Min Worldwide Deaths (Annual) Worldwide Deaths (Annual) Land Tsunami Asteroid Diameter (km) Asteroid Diameter (km)

6. The Four DEFT Scenarios: Other Considerations Remember: an impact scenario is unprecedented in historical times; there are no protocols to deal with one, nor is there a base of experience with an impact’s unique social and physical repercussions… • Aramis best simulates ever-changing (generally improving) knowledge of impactor and impact circumstances. Other cases would be similar. • Who will inform what officials about these threats? • Technical and political arguments in a context of worldwide anxiety and fear. • Preparation for evacuation, storing food, post-disaster relief (if deflection is uncertain or fails). http://www.aero.org/conferences/planetdef/Impact_Scenarios.pdf

7. Impacts of Practical Concern

8. Case Studies of Potential Impact Disasters(in my 2003 OECD study) • Civilization destroyer: 2-3 km asteroid or comet impact • Tsunami-generator: ~200 m asteroid impacts in the ocean • ~200 m asteroid strikes land • Mini-Tunguska: once-a-century atmospheric explosion (30-40 m body) • Annual multi-kiloton blinding flash in the sky (4 m body) • Prediction (or media report) of near-term impact possibility • Nature of Devastation. • Probability of Happening, in 21st century. • Warning Time. • Possibilities for Post-Warning Mitigation. • After-Event Disaster Management. • Advance Preparation. What can we do now? Six case studies, exemplifying the different sizes and types of impact disasters, were discussed in these terms: We just experienced Case (f) threatening a Case (d) LAST MONTH!

9. d. “Mini-Tunguska”: Once-in-a-Century Atmospheric Explosion • Nature of Devastation. 30-40 m “office building” rock hits at 100 times speed of jetliner, explodes ~15 km up with energy of 100 Hiro-shima A-bombs. Weak structures damaged/destroyed by hurricane-force winds out to 15 km. If over land, dozens or hundreds may die, especially in poor, densely populated areas (minimal damage in desolate places). • Probability of Happening. Once-a-century, but most likely over an ocean or sparsely-populated area. • Warning Time. Very unlikely to be seen beforehand; no warning at all. • Mitigation Issues. Little can be done in advance (an adequate search system would be very costly). Rescue and recovery would resemble responses to a “normal” civil disaster. No on-the-ground advance preparation makes sense, except public education about this possibility. Mini-Tunguska

10. f. Prediction (or Media Report) of Near-Term Impact Possibility • Nature of the Problem. Mistaken or exaggerated media report (concerning a near- miss, a near-term “predicted” impact, etc.) causes panic, demands for official “action”. • Probability of Happening. Has already happened several times, certain to happen again in next decade. Most likely route for the impact hazard to become the urgent concern of public officials. • Warning Time. Page-one stories develop in hours; officials totally surprised. • Mitigation Issues. Public education, at all levels of society: in science, critical thinking, and about risk, in particular. Science education and journalism need improvement with high priority.

11. The Impact that Didn’t Happen: AL00667, 13/14 January 2004 • Nominal MPC Confirmation Page ephemeris, based on 4 LINEAR positions, suggests impact in 24 hr (few hrs after Bush space speech) • Posting noticed by amateur astronomers, discussed on Yahoo’s MPML while MPC staff, professional astronomers “in the dark” • Cloudy skies in much of Europe and USA prevent definite follow-up • Steve Chesley (JPL NEO Program Office) calculates 10% - 25% chance of impact, in northern hemisphere, during next few days of ~30 m body • Midnight considerations to announce Torino Scale = 3 prediction • Lucky ad hoc e-mail connection enables amateur astronomer Brian Warner, with 20-inch telescope, to search for “virtual impactors” • Warner finds no object; LINEAR recovers object; calculations few hrs before Bush speech place it 10 times farther away, impact ruled out • Czech recovery next night provides designation 2004 AS1 LINEAR site in N.Mex.

12. Attributes of the AL00667 Case • Predicting imminent, “final plunge” impacts is not in the scope of the Spaceguard Survey (LINEAR, MPC, JPL NEO Program Office, NEODys, IAU WGNEO, etc.) • A system that notifies observers to “confirm” very preliminary NEOs necessarily makes the data public; and if data indicate a possible impact, they cannot be ignored • AL00667 positions had larger-than-usual uncertainties (we now know); but analysis of trajectories within usual uncertain-ties yielded 40% impacting the Earth; there was no mistake • But AL00667 data were delayed or held private; not available at all to experts at Lowell Observatory, Univ. of Pisa • Is a public announcement ethically required if there is a professional calculation of >10% impact chance? • Should Bayesian statistics be folded into calculation? • Communications network for AL00667 was mainly ad hoc, unfunded, and cannot be relied on in future • There have been only rudimentary (at best!) protocols, plans to handle out-of-scope, unexpected cases • For once, news media did not hype (or even notice) event The NEO Confirmation Page Brian Marsden Palmer Divide Observatory

13. Suggestions and Recommendations in Aftermath of AL00667 • Should Spaceguard infrastructure be enhanced to operate “24/7” and handle imminent impacts? • NO: mismatched priorities; only few-% chance that next small impactor will be seen before it hits • YES: only if “SDT Report” is implemented with system optimized to find smaller impactors • Should there be plans/protocols for best-effort handling of unexpected, out-of-scope cases? • YES: public expects responsible, professional responses; we were lucky this time • Instead of “one-night-stand” preliminary data being held private by LINEAR/MPC, should data be made immediately available to qualified international asteroid orbit specialists? • MPC says “NO”: unverified data can be misused • I say “YES”: preliminary, time-urgent, noisy data are normal in science; independent calculations are essence of open science. Why keep private? “SDT Report” August 22, 2003

14. NEO Impact Scenarios: Public Issues • Whether people actually “panic”, impact predictions generate anxiety and demands for action, for which no plans exist • The Torino Scale provides just a first cut estimate of how serious a prediction is (but remember Homeland Security scale!) • Public relations issues will evolve as technical knowledge about impactor, time, location of impact evolves • “Trustworthy” handling of deflection • Many unprecedented issues involving evacuation, contingencies, disaster relief • National, international responsibilities?

15. Public Perception • While “known” to many from movies and the news, a serious impact disaster has never been experienced in recorded history. • The tiny chances and huge consequences are extremely difficult for people to relate to. • The impact hazard is “dreadful” (fatal, uncontrollable, involuntary, catastrophic, increasing…) and apocalyptic (with religious or superstitious implications for many). Public response to a real impending impact is expected to be exaggerated (e.g. Skylab falling). • Experience with news media hype and misinformation suggests we need more science literacy among journalists and citizens in general.

16. Two-Tiered Approach to Dealing with Irrational Risk Responses • Public officials must be prepared to deal with disproportionate responses • The public politically demands that they do • There are real psychological, economic, and other consequences • Politicians, educators, and science journalists must endeavor to teach citizens how to evaluate more rationally the risks that affect them • Generally, fear would be reduced; rational concern would lead to constructive response • Our national and personal resources would be employed more cost-effectively