Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA, and “The B612 Foundation” Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA, and “The B612 Foundation” 32 nd Session of Erice International Seminars on Planetary Emergencies Erice, Italy 21 August nd Session of Erice International Seminars on Planetary Emergencies Erice, Italy 21 August 2004 RECENT PERSPECTIVES ON THE HAZARD OF AN ASTEROID IMPACT

The Hazard from Asteroids and Comets: Introduction 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. The Little Prince Meteorite punctured roof in Canon City, CO Global catastrophe Asteroid B612 Very recent review:

What Do We Know About the Impact Hazard? How many asteroids and comets 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 How much energy is delivered by an impact (e.g. the TNT equivalence, size of resulting crater). environmental consequences How much dust is raised into the stratosphere and other environmental consequences. Biosphere response Biosphere response (agriculture, forests, human beings, ocean life) to environmental shock. psychology, sociology, political systems, and economies September 11 th terrorist attack? Response of human psychology, sociology, political systems, and economies to such a catastrophe. September 11 th terrorist attack? WE KNOW THIS… Very Poorly Somewhat Very Well Very Well

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 Scientific American

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

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

Death Threat from Impacts, by Asteroid Diameter and Location of Impact Statistical mortality from impacts, post-Spaceguard (2010+), 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 additionally they 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. Worldwide Deaths (Annual) Asteroid Diameter (km) Max Nominal Min Tsunami Land Global (For nominal case)

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

Fatality Rates Compared with Accidents and Natural Hazards

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

Impacts of Practical Concern

Case Studies of Potential Impact Disasters (in Chapman 2003 OECD study) 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: a.Civilization destroyer: 2-3 km asteroid or comet impact b.Tsunami-generator: ~200 m asteroid impacts in the ocean c.~200 m asteroid strikes land d.Mini-Tunguska: once-a-century atmospheric explosion (30-40 m body) e.Annual multi-kiloton blinding flash in the sky (4 m body) f.Prediction (or media report) of near- term impact possibility 13 January 2004: AL00667 was Case (f) masquerading as a Case (d)! Lessons must be learned.

a. Civilization-Destroyer: 2-3 km Asteroid or Comet Impact Nature of Devastation. A million MT explosion, global climate catastrophe, growing season lost worldwide; firestorm as big as India; ozone layer destroyed; no nation spared severe consequences; civilization threatened by collapse of social and economic institutions; billions might die. (Unprecedented, so uncertain.) Probability of Happening. Most 2-3 km bodies are known, will NOT hit soon. Residual ones: ~1-in-100,000 chance/century. Warning Time. If asteroid, decades; if a comet, few months. Possibilities for Post-Warning Mitigation. Years-to-decades warning. Deflection could avert impact, but very technically challenging for such a big object. If warning time is too short (or deflection fails). Mass evacuation near ground zero; production/storage of food; hardening of susceptible infrastructure (medical services, communications, transportation). Very challenging. After-Event Disaster Management. (See “Lucifer’s Hammer”) Advance Preparation. So rare, little useful to do other than “out-of-the-box” thinking that might prepare for other “unthinkable” disasters and help at the margins.

d. “Mini-Tunguska”: Once-in-a- Century Atmospheric Explosion Nature of Devastation 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

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 anxiety, 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.

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 (e.g. 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 is falling,” or post-9/11 fears of terrorism). Scientific illiteracy prevails among public, journalists, and officials (hurricane Charley) Odds of a “Royal Flush” (1 in 649,739) are like chances of a mile-wide asteroid striking next year!

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

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]

NEO Impact Scenarios: Public Issues Whether or not people actually “panic”, impact predictions generate anxiety and demands for governmental action, for which no plans exist The Torino Scale provides just a first cut estimate of how serious a prediction is (but Homeland Security scale hasn’t worked!) Public relations issues will evolve as technical knowledge about impactor, time, and location of predicted impact evolves “Trustworthy” handling of deflection Many unprecedented issues involving evacuation, contingencies, disaster relief National vs. international responsibilities?

Events and Developments, (1 of 2) NASA SDT report recommends Spaceguard Survey down to 140 m Serious discussion of NEA properties and deflection practicalities Sept NASA “Mitigation Workshop” proceedings out by end of 2004 (Camb. Univ. Press) AIAA/B612 “Planetary Defense Conference,” Feb on-line at: Small-body groundbased/spacecraft studies Radar and adaptive optics resolve asteroid moons Unexpected nucleus geology for Comet Wild 2 Deep Impact launch Dec. 2004, cratering of comet Temple 1 in summer 2005 Hayabusa begins 5-month study of NEA summer 2005, returns samples to Earth in summer 2007

Events and Developments, (2 of 2) Two NEA “events” in early 2004 AL00667 was estimated ~30 m in size with 10-40% chance of impacting northern hemisphere in next few days FH missed Earth by one Earth-circumference on 18 March 2004; it was, in fact, ~30 m in diameter. Both events highlight uncertainty in lower threshold size for damage on the ground: is it ~25 m or ~50 m? Some developing interest of social scientists in the impact hazard ICSU “Workshop on Comet/Asteroid Impacts and Human Society,” Tenerife, 27 Nov. – 2 Dec Natural hazards community disrupted (at least in U.S.) with new priorities in post-9/11 period; role of impact hazard (as an example of extreme events) is uncertain.

The Impact Threat: Conclusions Its potential consequences are horrific… exceeding any other natural hazard and equaling 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