Potential Impact Disasters: Near-Earth Object Hazards and Society

1. How a Near-Earth Object Impact Might Affect Society Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Commissioned by the OECD Global Science Forum Workshop on Near Earth Objects: Risks, Policies, and Actions Frascati, Italy 20 January 2003

2. The Hazard from Asteroids and Comets • 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.

3. 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

4. Comets and Asteroids The processes that formed the planets 4.6 billion years ago left many small remnant objects: comets (beyond the outer planets) and asteroids (in a “belt” between the orbits of Mars and Jupiter). Some of them occasionally cross the Earth’s orbit and can strike our planet...if it happens to be there at the same time. Comets Jupiter’s orbit We are Here! Asteroid Belt Sun NEOs Comets come from far beyond Jupiter Two asteroids colliding

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…” • In this talk, I 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 Six 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. Tsunami-Generator: ~200-meter Asteroid Impacts in Ocean • Nature of Devastation.Flying mountain, size of NASA-VAB, at 100 times jet-airliner speed, strikes ocean (~600 MT). Tsunami >10 m height (comparable to biggest historical cases) would devastate coasts around entire ocean rim, ranging up to kilometers inland; millions might die. Locally highly variable. • Probability of Happening.One chance in several hundred (worldwide chances this century). Land-locked countries mostly unaffected. Greatest threat is for countries with coasts on the largest oceans. • Warning Time. (a) <20% chance astronomers will discover the asteroid before impact, >80% chance it hits ocean without warning; (b) up to hours of warning if detected by Pacific Tsunami Warning Center; (c) advance tsunami warning possible for other oceans, but warning infrastructure is poorly developed.

10. Case A, continued: Tsunami-Generator: ~200-meter Asteroid Impacts in Ocean • Post-Warning Mitigation Possibilities. (a) deflection of asteroid (if discovered before impact); otherwise (b) evacua- tion to higher ground (if tsunami warning infra- structure is in place and works). • After-Event Disaster Management. Would resemble rescue efforts required following other record-setting natural disasters; unaffected locales several km inland could be centers for recovery efforts. • Advance Preparation. (a) development of tsunami- warning systems for all oceans; (b) recognition of different nature and signatures of impacts compared with earthquake-generated tsunami; (c) bathymetric studies of topography near populated areas could guide local planning; (d) enhancement of tsunami-protection infrastructure, recognizing that asteroid-tsunami may be larger than any previously considered.

11. B. ~200-meter Asteroid Strikes Land • Nature of Devastation. Same 600 MT explosion, but creates 4 km crater deeper than the Grand Canyon. City-sized area pulverized. Severe blast damage and fire 50 km in all directions. Earthquake, falling rocks, smoke, dust, etc. hundreds of km away. Destroys a small nation or modest-sized American state. Death toll: thousands to hundreds of thousands (could be millions or just a few). • Probability of Happening. One-in-1000 during 21st century. Russia, Canada, China, USA, Australia, Brazil most likely targets. • Warning Time. (a) <20% chance astronomers will discover asteroid long before impact; (b) >80% chance of strike without warning. Persons who witness strike from afar may have seconds to tens-of-seconds to take cover. The crater would be 6 times wider and deeper than Meteor Crater in Arizona, shown here.

12. Case B, continued. 200-meter Asteroid Strikes Land • Possibilities for Post-Warning Mitigation. Only if asteroid were detected in advance, possibility of deflection by Apollo Program-level space technology project (if not, there is no warning at all). • After-Event Disaster Management. Enormous zone of death and destruction, with combined effects of earthquake, Krakatoa-like volcanic explosion, typhoon, & firestorm rolled into one. No unusual lingering effects (e.g. no radioactivity), but unprecedented issues of health, panic, and despair to be dealt with (cf. Garshnek et al., 2000). • Advance Preparation. All places are equally likely to be the target. Normal emergency management protocols designed for extreme windstorms, fires, and earthquakes (which are much more likely to occur as a normal, terrestrial natural disaster than from an impact) would apply. But, unless the asteroid is discovered before it hits, there is little justification for asteroid-specific mitigation measures (except at the margins).

13. C. “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.

14. D. Annual, Multi-Kiloton Blinding Flash in the Sky • Nature of Devastation. A bus-sized boulder explodes 20 km up in the stratosphere with the energy of a small A-bomb (2 to 10 kT). The blinding flash is brighter than the Sun. No ground damage. But in a zone of military tension, such an event might be misinterpreted as an atomic attack, triggering an inappropriate response. • Probability of Happening. Annual event, somewhere on Earth. Far less likely to happen over a war zone. • Warning Time. No warning at all. • Mitigation Issues. Such events are regularly observed by U.S. Depts. Of Energy & Defense, information made available to public on timescale of weeks (?), probably not immediately to all who might be concerned. Level of knowledge among military agencies of other countries not known to me. Clearly, education about the possibilities of such events (in the context of various national military command-and-control structures) would help.

15. E. 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.

16. Case E, 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.

17. Case E, 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 marginal extra effort 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.

18. 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.

19. Case F, 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)

20. The Torino Scale Events Having No Likely Consequences Events MeritingCareful Monitoring Events MeritingConcern ThreateningEvents CertainCollisions

21. Issues that Affect Societal Response • Public Perception • Issues of subjectivity vs. objectivity • Role of news media, scientific literacy • Scientific Uncertainty and “meta errors” • Other Natural Hazards/Civil Defense • Impacts in context of other disasters • Lessons from thinking about an extreme • Asteroid Deflection • Insights after September 11th

22. 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.

23. 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.

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

25. Headline: “Mile-Wide Asteroid Will Hit in 2024” Which is least likely to be correct? A. The news report is wrong due to bad or hyped journalism. B. The scientific forecaster goofed. We’re safe. C. The astronomers erred. The asteroid is tiny; most of the world is safe. D. An asteroid will hit Earth in 2024. The correct answer is “D”: A, B, and C are all much more likely to explain the headline.

26. 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.

27. Scientific Uncertainty • Science is taught as “fact” but it is, actually, a process dominated by uncertainty • Even in normal interactions with scientists, public “users” of science rarely appreciate “error bars” (statistical, systematic) • The impact hazard has augmented(“meta”) errors: • Because one hasn’t happened, and large impacts far exceed the biggest bomb tests, our understanding of consequences is based on uncertain extrapolations • The chances of impact are so tiny that it is more likely that scientists will err in predicting impacts than that an impact will happen Warning to public officials: “Buyer beware!”

28. 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

29. 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.

30. Fatality Rates Compared with Accidents and Natural Hazards

31. Deflecting an NEO Away from Earth • Spacecraft technologies exist (but piecemeal, requiring system design/integration) to deliver deflection devices to an Earth-targeted NEO, given years/decades warning and lead-time. • The NEAR-Shoemaker spacecraft actually landed on the NEO Eros in 2001 • Powerful devices have been proposed: anchored bombs or stand-off neutron bomb • These could break up the object into several dangerous pieces, rather than move it intact • Low-thrust device options: plasma engine, solar sail, mass driver, boiling surface by powerful laser, even “paint-it-black” to take advantage of the so-called Yarkovsky Effect • Issues of “deflection dilemma” and trustworthy design of even low-thrust deflection (Schweickart)

32. Post-September 11th Insights • We’ve “learned” to expect 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 (I was charged $4 for a plastic cup of wine flying over the Atlantic to this meeting!) and the resulting potential losses (e.g. economic recession). • “Who was to blame for not foreseeing this kind of disaster?”

33. Current Dilemma. (Maybe this OECD meeting is a start to fixing it!)