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

1. http://www.boulder.swri.edu/clark/clark.html IDENTIFYING THE PROBLEM OF NEOs: WHY WE ARE HERE The asteroid impact hazard and interdisciplinary issues Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA Introductory Keynote Presentation ICSU Workshop: Comet/Asteroid Impacts and Human Society Santa Cruz de Tenerife 29 November 2004

2. 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) • 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 1900s 1960s 1980s 1990s Meteorite punctured roof in Canon City, CO Meteor Crater Global catastrophe

3. Goals of this Keynote Talk… • To translate what astronomers and physi-cists have learned about asteroids and the impact hazard into familiar frameworks • To summarize (from an astronomer’s perspective) issues relevant to social scientists and policy makers • To foster thinking about this hazard to inspire a serious evaluation of how (and to what degree, if at all) society should become proactive about this threat My very recent review of the physical-scientific features of the hazard: http://www.boulder.swri.edu/clark/crcepsl.pdf My OECD report on how different impact scenarios might affect society: http://www.boulder.swri.edu/clark/oecdjanf.doc

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. September 11th terrorist attack? WE KNOW THIS… Very Poorly Somewhat Very Well Very Well

5. Comets & Asteroids: NEAs, NEOs 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...ifit 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

6. Sizes and Numbers of NEAs… and How Often They Hit

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

8. Environmental Consequences of Big Impacts • Total destruction in crater zone • Destruction zone 30 times the size of the asteroid • Tsunami (“tidal waves”) • Huge waves run up shores of impacted ocean • Stratospheric dust obscures sun • Agriculture ceases around the globe for a year • Global firestorm from meteor storm • Re-entering ejected material broils Earth’s surface • Poisoning of the biosphere • Sulfates, nitric acid, ozone layer destroyed… • Earthquakes • Modest effects compared with everything else

9. Visualize the Widely Different Impact Scenarios • Global, civilization-threatening horror (>2 km diam., 1 chance in 10,000 21st C.) • Regional catastrophe (e.g. tsunami destroys everything within few km of Pacific Rim)(300m-1.5km, 0.2% chance 21st C.) • Devastating local disaster (30m - 300m, 40% chance 21st C.) • Blinding Hiroshima-scale flash in sky (happens every few years) • Media hype, false alarm (happens every few months) OVER KASHMIR? OVER ISRAEL? HOW WOULD THE GENERALS RESPOND?

10. Impacts of Practical Concern: From my OECD Talk (2003)

11. 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 (deaths, not SDT’s 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 NEO astronomers and public officials. (For nominal case) Global Max Nominal Min Worldwide Deaths (Annual) Worldwide Deaths (Annual) Land Tsunami Asteroid Diameter (km) Asteroid Diameter (km)

12. 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 to 1 km) • NASA SDT proposed 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 Kitt Peak Natl. Observatory B612 Project : see Schweickart et al., Nov. 2003 Scientific American

13. Fledgling Attempts at Disaster Management and Preparation • Astronomers trying to communicate with… • the public (via science journalists: Torino Scale) • government officials (e.g. up NASA hierarchy) • Warning system beyond NASA not devised • to Dept. of Homeland Security (HSPD-5) • to military/civil defense agenices • to the rest of the world • Minimal awareness of impact hazard in national/international “all-hazards” planning • similarities in many causes of lethality (flying objects, fire, smoke, floods) • unique dissimilarities (psychological, physical: no radiation or precursors, not willful, etc.) • this “end-member” example has much to teach about unexpected, extreme disasters

14. Chances from Dying from Selected Causes (for U.S.A.) By terrorism (mostly due to Sept. 11th attacks) 9/11

15. Fatality Rates Compared with Accidents and Natural Hazards

16. 20th Century Catastrophes: We have much more to worry about! Source: John Pike • Averaged over long durations, the death rate expected from NEO impacts is similar to that from volcanoes.

17. 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 1.5 km-wide asteroid striking next year!

18. Common Misperceptions • Long waiting time until next impact • instead, we should think of chances of disaster • Judging consequences quantitatively • civilization-ending impact vs. K/T mass-extinction • “one death” vs. 100 deaths/yr vs. 3000 9/11 dead vs. we will all die in next 100 years • Shoemaker-Levy 9 Jupiter impacts overshadowed the Rwanda genocide in the news (July 1994) • “Blow it up” on the way in • movies misrepresent reality of decades lead-time • NEA is “on an impact course with Earth” • NEA discovery process, error ellipses, NEA orbits the Sun many times before impact: not intuitive! Part of very elongated error ellipse

19. Societal Impacts: (1) The News Media • A “near miss” (maybe just happened) • An actual bolide/fireball (hits a house) • Prediction of very small chance of a big impact decades in the future A 2002 BBC-online report said an NEA was “on a collision course with Earth” when the astronomer’s press release actually said that it would miss by 10’s of millions of km and the impact probability estimate was never higher than one-chance-in-100,000. There are some excellent science journalists who understand the subtleties, but people are increasingly scientifically illiterate and get news about NEOS from TV “weathermen” and others who often hype the story.

20. Societal Impacts: (2) Religion and (3) the Military • Asteroid impacts and the Apocalypse • web sites are filled with asteroid prophecies • Halley Comet 1910 pass was ‘end of world’ • late-night radio shows on “the fringe” • how would believers respond to a real threat? • Is ‘Planetary Defense’ a Military Job? • US Air Force funds NEO searches, reports bolide events, but takes no responsibility • NASA vs. Dept. of Energy vs. Dept. of Defense • Treaties ban use of bombs in outer space • UN COPUOS has sponsored NEO meetings • Asteroids as disarmament “bargaining chips” • Do war-zone generals understand bolides?

21. Societal Impacts: (4) the Scientific Community • Modern astronomy is rarely “practical” • NEOs are unique (except for solar flares) • Very unlike the practical sides of geosciences • NASA late-OSS funded “pure science” • NEAR-Shoemaker (landed on Eros) had purely scientific goals (origin/evolution of solar system) • Congress forced minor funding for NEO search • NEOs are prominent in “informal” science education (museums, TV documentaries) – giant mismatch with funded research • More open-minded in Europe & Japan, but budgets are inadequate to support major focus on NEA research • Integration needed between astronomers and the social sciences/policy makers

22. Conclusions: What Do We Do? • Humans have the intelligence and technology to protect society from the asteroid threat. The dinosaurs failed. • The threat from the skies is real but it is also very improbable. (It can teach us about other extreme hazards.) • Many threats to society and our lives (flu, war, famine…) are more immediate. • Can we rationally evaluate the priority of the NEO threat and undertake an international program to appropriately deal with this global issue?