Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA

1. http://www.boulder.swri.edu/clark/clark.html Consequences of Predicted or Actual Asteroid Impacts Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Session U22B: “Estimating the Consequences of Severe Geophysical Events” AGU Fall Meeting San Francisco 9 December 2003

2. In the Post 9/11 World... What are the potential consequences of the remote threat of an asteroid impact catastrophe?

3. The Hazard from Asteroids and Comets: Introduction The Little Prince • The Earth encounters interplanetary projectiles, ranging from (a) tiny, harm- less ones to (b) gigantic, destructive ones…(the big ones hit very rarely). • This is a newly recognized threat • Comet fears…Watson, Baldwin, Opik (NEAs,1950s) • Shoemaker/Meteor Crater…Mariner spacecraft • Alvarez et al. K-T Boundary hypothesis/Chicxulub • Spaceguard NEA “near misses”/disaster movies • This extreme example of a natural disaster (tiny chances of happening, but with huge consequences) challenges a rational response by citizens and policy-makers. Asteroid B612 Meteorite punctured roof in Canon City, CO Global catastrophe

4. What Do We Know About the Impact Hazard? • How many asteroids and comets there are of various sizes in Earth-approaching orbits (~1100 > 1 km diam.) So impact frequencies are known. • How much energy is delivered by an impact (e.g. the TNT equivalence, size of resulting crater). • How much dust is raised into the stratosphere and other environmental consequences. • Biosphere response (agriculture, forests, human beings, ocean life) to environmental shock. • Response of human psychology, sociology, political systems, and economies to such a catastrophe. Sept. 11th? NE USA 2003 Blackout? WE KNOW THIS… Very Poorly Somewhat Very Well Very Well

5. 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

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

7. Risk vs. Scale of Impact(Chapman & Morrison 1994) • Annual fatalities peak for events near the global “threshold size”, about 2 km • Orange/yellow zone illustrates our range of uncertainties for agricultural disaster due to stratospheric dust • Tsunami risk very uncertain Stratospheric Dust Tsunami

8. NASA Re-evaluation of Risk(NEO Science Definition Team, August 2003) • NEO population estimates • Residual impact hazard (after Spaceguard finds 90% of NEAs >1 km diameter, 2008) • Candidate technologies and search strategies (ground-based & space-based) to retire more of the risk (by identifying objects that won’t hit, or one that will) • Cost-benefit analysis Recommendation: Extend survey to discover 90% of Potentially Hazardous Objects >140 m diameter, in a ~$300 million program taking 7 to 20 years beginning in 2008. Statistical global mortality would drop from 300 to 30 deaths per year.

9. Deaths due to Land Hazard, Tsunami Hazard, Global Hazard 16 • “People Affected” Annually • Deaths for land and global • Tsunami inundation • Maximum, Nominal, Minimum • Comets < 1% of Hazard: it’s NEAs! • Overall vs. Residual Hazard (after SG) 0 0.04 km 1 km 8 km 60 800 0 0 0.04 km 1 km 8 km 0.04 km 1 km 8 km 6 Deaths are ~10% of people affected by tsunami

10. Overall Impact Hazard • Total impact hazard is dominated by global catastrophes…but Spaceguard is finding most NEAs >1 km diam., so residual hazard will soon be dominated by 60-600 m NEAs • Dividing tsunami risk by 10, residual risk is: • 33% from land impacts (60 – 200 m diam.) • 10% from tsunami (asteroids 150–600 m diam.) • 57% from global catastrophes (1-2 km diam.) • Statistical annual worldwide mortality: • 36 minimum estimate • 155 nominal estimate • 813 maximum estimate (Comparable with airliner fatalities) Numbers in official table (left) weigh property damage from tsunami more heavily

11. Chances from Dying from Selected Causes (for U.S.A.) By terrorism (mostly due to Sept. 11th attacks)

12. Fatality Rates Compared with Accidents and Natural Hazards

13. 20th Century Catastrophes: We have much more to worry about! Source: John Pike • Averaged over long durations, the death rate expected from impacts is similar to that from volcanoes.

14. What Can We Do about This Hazard? What Are We Doing about It? • We can use telescopes to search for asteroids and comets that might be on a collision course with Earth during this century (e.g. Spaceguard Survey) • NASA report proposes extension to 140 m • If one is found (among all those that we can certify as not a threat), then we could mitigate (evacuate, amass food supplies, move the asteroid so it won’t hit, etc.) • Low-thrust propulsion (e.g. B612 demo. project) could deflect NEA away from us See Schweickart et al., Nov. 2003 Scientific American

15. “Of no practical concern…” But YOU may disagree! • I will de-emphasize the extremes… • OBJECTS SMALLER THAN A FEW METERS ACROSS • they can damage satellites in space, but have no practical consequences on the ground, are essentially harmless (when they cause minor harm, they make headlines) • OBJECTS LARGER THAN A FEW KM IN SIZE • these are philosophically important: they have shaped evolution of life on Earth (mammals arose from the dinosaurs’ demise); another such impact could eradicate the human species • BUT the chances are extremely remote of such an impact in our lives; there’s little we could do in advance to protect ourselves from the resulting holocaust, anyway • So my Case Studies concern a broad mid-range, several meters to several km diam.

16. Impacts of Practical Concern

17. Case Studies of Potential Impact Disasters(abridged from my OECD study) Three case studies, exemplifying the different sizes and types of impact disasters, are discussed in these terms: • 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?

18. A. Civilization-Destroyer: 2-3 km Asteroid or Comet Impact • Nature of Devastation. A million MT explosion, global climate catastrophe, growing season is lost worldwide. Firestorm the size of India. Ozone layer destroyed. No nation spared severe consequences. Compound effects threaten civilization by collapse of social/economic institutions. Billions might die. (Unprecedented, so predictions uncertain.) • Probability of Happening. Most 2-3 km bodies are known and will NOT hit soon. Residual ones have ~1-in-100,000 chance of striking in 21st century. • Warning Time. If an asteroid, decades; if a comet, few months. • Possibilities for Post-Warning Mitigation. • Discovered years to decades in advance. Deflection would avert disaster, but very technically challenging for such a big object. • If warning time is too short (or deflection fails). Mass evacuation of sector near ground zero; production/storage of food and other preparations for crisis; hardening of susceptible infrastructure (communications, transportation, medical services). Extraordinarily challenging; ineffective if warning time were only months.

19. Case A, (continued). Civilization-Destroyer: 2-3 km Asteroid or Comet Impact • After-Event Disaster Management.Wholly unprecedented. History (Dark Ages, Plague) or fiction (e.g. “Lucifer’s Hammer”) provide best perspectives. • Advance Preparation. • Considering such an extreme case encourages“out-of-the-box” thinking about other unanticipated future crises. • Deflection would be so challenging, advance work (e.g. learning how to move a smaller asteroid) would be good preparation. • In normal international disaster planning and coordination, extra effort at the margins to consider such an apocalyptic horror might define the outer-envelope of contingencies.

20. B. “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 Hiroshima A-bombs. Weak structures damaged/destroyed by hurricane-force winds out to 20 km. Hundreds die; mostly 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.

21. C. Prediction (or Media Report) of Near-Term Impact Possibility • Nature of the Problem. Mistaken or exaggerated media report (near-miss, near-term “predicted” impact, etc.) causes panic, demands for official “action”. • Probability of Happening. Already happened! Certain to happen again soon. This is the most likely way for the impact hazard to become of urgent concern to public officials. • Warning Time. Page-one stories develop in hours; officials totally surprised. • Mitigation Issues. Public education in science, critical thinking, and about risk, in particular. Science education and journalism need much improvement.

22. Case C, (continued). Prediction (or Media Report) of Near-Term Impact Possibility Examples LESSON: Perception drives the most likely consequences! • Actual “near miss” by >100 m asteroid, “just” 60,000 km from Earth. Will people believe official statements it will miss? • Reputable but mistaken astronomer predicts huge impact will occur on, say, 1 April 2017 in a specific country; report not withdrawn for few days; panic results. • Official IAU prediction of 1-in-few-hundred impact possibility later in century (Torino Scale = 2); not refined for months. • Grotesque media hype of one of above cases or other innocuous fact (3 cases last year)

23. 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, huge consequences are extremely difficult for people to relate to (building in 100 year floodplains.) • 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, or 9/11). Odds of a “Royal Flush” (1 in 649,739) are like chances of a mile-wide asteroid striking next year!

24. Hazard Scales: The Challenge of Simply Communicating Risk to Citizens • The well-known Richter Scale has been refined over decades. • Americans wrestled this spring with how to deal with “orange”. • The Torino Scale has had modest effectiveness, challenges. Terrorism Scale Richter Scale (Earthquakes) Predicted Asteroid Impact Scale

25. Comparisons with other Natural Hazards and with Terrorism • Similar to Terrorism • Threats are new, “dreadful”, poorly understood, raise fears • Few have been (or will be) killed, but many could be killed • Both strike “randomly”, in place and time • Dissimilar from Terrorism • Impacts are an “act of God”; terrorism is conscious evil • We can do something concrete to deflect an asteroid; battling terrorism is like waging the “war on drugs” • We spend a few million on Spaceguard, hundreds of billions to battle terrorists (how much on flu vaccinations?) • Similar to Natural Disasters:nature of damage mostly due to familiar forces (fire, high wind, quake, falling debris, flood) • Dissimilar from Natural Disasters: impacts happen any-where; no “aftershock” analogs; no radioactivity or enemy soldiers

26. Post-September 11th Insights • We’ve “learned” to fear the unexpected in what seems like an ever more risky world -- whether or not it truly is.(Asteroids appear to be an increasing danger, even though they aren’t, due to increasing “near misses”. Terrorism isn’t “increasing” much either: 2544 1983-93 vs 4376 1993-2003.) • “Objective” measures of death and damage (e.g. ~3000 deaths and property damage in lower Manhattan) do not begin to predict the nature of public responses and the resulting potential losses (e.g. economic recession). • “Who was to blame for not foreseeing this kind of disaster?” (we seek villains in government, for 9/11, for the Columbia disaster…who will be blamed if an asteroid strikes?)

27. Wrapping up the Impact Threat: • Its potential consequences are horrific… exceeding any other natural hazard and equalling all-out nuclear war • Unlike the dinosaurs, we have the intelligence and technology to avert a threatened impact • In a post-September 11th world, it is difficult (for me) to predict public reactions to near-misses, huge-but-low-probability disasters, bombs in space, and other impact hazard issues • Predictions of consequences involve psychology/ sociology/politics as much as geophysics • The impact hazard is REAL but it is VERY UNLIKELY that a big impact will happen during our lifetimes

28. Asteroid Impact Hazard Impact frequencies and projectile sizes There is an enormous variety of projectiles from interplanetary space that impact the earth. Reading clockwise from the upper left, there are dust grains that create “shooting stars” all the time to the “dinosaur killers” that strike only about once every hundred million years. The table shows the range of threatening impactors of practical concern, ranging from the “civilization destroyer” down to the “harmless” 2 kiloton atmospheric blast, which however could be mistaken for a nuclear attack in a place of international tension. SwRI researchers in Boulder are evaluating the impact hazard and what might be done about it.