Understanding the Asteroid Impact Hazard

1. Perspectives on the Impact Hazard in a Dangerous World Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA The Asteroid/Comet Impact Hazard: A Decade of Growing Awareness American Association for the Advancement of Science, Annual Meeting Denver, Colorado 14 February 2003

2. In the Post 9/11 World... Does the remote threat of an asteroid catastrophe have anything to teach us?

3. The Hazard from Asteroids and Comets: Re-cap • The Earth encounters interplanetary projectiles, ranging: (a) tiny, harmless ones; (b) gigantic, destructive ones… (and everything in between). • The most dangerous ones are very rare but very destructive. Smaller impacts, with greater chances of happening soon, also merit practical concern by relevant public officials. • This extreme example of a natural disaster (tiny chances of happening, but with huge consequences) challenges a rational response by citizens and policy-makers.

4. What Do We Know About the Impact Hazard? • How many asteroids and comets there are of various sizes in Earth-approaching orbits (hence, 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. 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 K-T mass extinctor, 65 Myr ago Tunguska, 1908 Millenniunm Mountain 500,000 yr SL9 hits Jupiter 1994

6. “Of no practical concern…” • I will de-emphasize the extremes… • OBJECTS SMALLER THAN A FEW METERS ACROSS • although they can damage satellites in space, they have no practical consequences on the ground, are essentially harmless (when they cause minor harm, they make the news) • OBJECTS LARGER THAN A FEW KM IN SIZE • these are philosophically important, because they have shaped the evolution of life on Earth (mammals arose from the dinosaurs’ demise) and another such impact could eradicate the human species • BUT the chances of such an impact are extremely remote, and there’s not much we could do in advance to protect ourselves from the resulting holocaust, anyway • So I will discuss a broad mid-size range, several meters to several km in diameter ???

7. Impacts of Practical Concern

8. Case Studies of Potential Impact Disasters 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?

9. A. Civilization-Destroyer: 2-3 km Asteroid or Comet Impact • Nature of Devastation. A million MT explosion, whether on land or ocean, yields global climate catastrophe. Enormous regional destruction pales in comparison with global havoc as growing season is lost worldwide. Firestorm the size of India. Ozone layer destroyed. No nation spared severe direct consequences. Compounded disasters threaten future of civilization due to collapse of social and economic institutions. Hundreds of millions to billions might die. (Since this case is so extreme compared with anything ever experienced, its features are very uncertain…a 1 km asteroid might suffice, or it might take a 5 km impactor.) • Probability of Happening. Many bodies of this size have already been discovered and will NOT hit in near future. Remaining, undiscovered bodies (mainly comets) have 1-in-50,000 to 1-in-100,000 chance of striking in 21st century. • Warning Time. If an asteroid, excellent chance it would be known decades in advance. If a comet, only a few months to a few years notice.

10. Case A, continued (1). Civilization-Destroyer: 2-3 km Asteroid or Comet Impact • Possibilities for Post-Warning Mitigation. • Discovered many years to decades in advance. Deflection of the asteroid 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 of Earth near ground zero; production/storage of food and other preparations for crisis; hardening of susceptible elements of civilization’s infrastructure (communications, transportation, medical services). Extraordinarily challenging; probably ineffective if warning time were only months. • After-Event Disaster Management.Wholly unprecedented. History (Dark Ages, Plague) or fiction (e.g. “Lucifer’s Hammer”) might provide best perspectives.

11. Case A, continued (2). Civilization-Destroyer: 2-3 km Asteroid or Comet Impact • Advance Preparation. • Although extremely unlikely and wholly unprecedented, considering such an extreme case can encourage “out-of-the-box” thinking about other unanticipated future crises. • Diverting the object from hitting Earth would be extremely challenging, so advance work on initial steps (e.g. learning how to move a smaller asteroid) would be good preparation. • In normal international disaster planning and coordination, it would be worth extra effort at the margins to factor such a catastrophe into the thinking, to define the outer-envelope of contingencies. Lesser disasters might be more readily addressed in a context in which there has been thinking about the massive, global effort that would be required to address and recover from such an apocalytic horror.

12. B. “Mini-Tunguska”: 1-in-a-Century Atmospheric Explosion • Nature of Devastation. 30-40 m “office building” sized rock hits at 100 times speed of jetliner, explodes ~15 km up in atmosphere with energy of 100 Hiroshima A-bombs. Weak structures damaged/destroyed by hurricane-force winds to 20 km distance. Hundreds die; more deadly in poor, densely populated area but minimal damage in desolate regions. • Probability of Happening. Once-a-century, but most likely over an ocean or spasely-populated area. • Warning Time. Very unlikely to be predicted in advance (without major augmentation of discovery searches), hence 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 educating public about this possibility.

13. C. 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.

14. Case C, continued. Prediction (or Media Report) of Near-Term Impact Possibility Examples • 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 specfic 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 last year)

15. Badly Misleading News Stories in 2002 Alone • 2002 EM7 came from a “blind spot,” it was a near-miss, so the Spaceguard Survey is inadequate • Many NEOs are found departing. Goal never was to catch one just before impact. Reflects basic misunderstanding of survey approach. • 2002 NT7 “is on an impact course with Earth” (BBC, July 2002) and other hyperbole • It was a scientifically interesting case of a very small chance of impact many years from now; as usual, a few days of further observations reduced the chances to zero. • “Impact dangers less than we thought” (attributed to Brown et al., Nature, Nov. 2002) • Brown et al. studied harmless objects 1 to 10 m in size; no implications for “Tunguskas” let alone for the several km NEOs, which actually dominate the hazard, statistically.

16. A Royal Flush (UPDATE:This statistic has changed in the last few years as we have discovered most of the mile-wide asteroids and learned that those won’t strike Earth: now there’s a slightly better chance of getting a Royal Flush than death-by-asteroid next year!) Odds:1 to 649,739 • It is more likely that a mile-wide asteroid will strike Earth next year than that the next poker hand you are dealt will be a royal flush.

17. 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.

18. NEO Impacts in the Context of Natural Hazards and Civil Defense • Impact hazard has similarities and dissimilarities compared with more familiar disasters • Similarities include: nature of damage partly caused by familiar forces (fire, high wind, quake, falling debris, flood) • Dissimilarities: impacts happen anywhere; no analogs to “aftershocks”; no radioactivity or enemy soldiers • Though a major impact could happen, it is much less likely than a familiar natural disaster • For every future impact that will kill thousands to hundreds of thousands of people, there will likely be hundreds of floods, typhoons, and earthquakes that will each kill just as many

19. Fatality Rates Compared with Accidents and Natural Hazards

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

21. 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.

22. Current Dilemma. (FEMA has shown little interest, for example.) What should we do to develop the institutional capability to respond to a predicted or actual impact? Astronomers have tried to take the first step...

23. The Torino Scale (How to React to a Published Prediction of a Future Impact) Events Having No Likely Consequences Events MeritingCareful Monitoring Events MeritingConcern ThreateningEvents CertainCollisions

24. Warnings! (It’s a Dangerous World) UV Index Nuclear Plant Event Air Quality Hurricane Doomsday Computer Virus Fire Danger Wind Damage

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

26. Comparisons of Terrorist Threat and Impact Hazard • Similarities • Threats are new, “dreadful”, poorly understood, raise fears • Few have been (or will be) killed, in all likelihood…but many could be killed • Both strike randomly, in place and time • Dissimilarities • Terrorism is consciously done (so retribution is demanded) while impacts are an “act of God” • We can do something concrete about the impact hazard (search for the body that may impact, deflect it, or evacuate ground-zero); battling terrorism is like the “war on drugs” • We spend vast sums to battle terrorists, a few million $ annually to search for asteroids (and how much on flu vaccination programs that might save 20,000 annually?)

27. 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”.) • “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?)

28. 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