Clark R. ChapmanSouthwest Research Institute Boulder, Colorado, USA,

and “The B612 Foundation”

Clark R. ChapmanSouthwest Research Institute Boulder, Colorado, USA,

and “The B612 Foundation”

3232ndnd Session of Erice International Seminars Session of Erice International Seminars on Planetary Emergencieson Planetary Emergencies

Erice, Italy 21 August 2004Erice, Italy 21 August 2004

3232ndnd Session of Erice International Seminars Session of Erice International Seminars on Planetary Emergencieson Planetary Emergencies

Erice, Italy 21 August 2004Erice, Italy 21 August 2004

RECENT PERSPECTIVES ON THE HAZARD OF AN ASTEROID IMPACTRECENT PERSPECTIVES ON THE

HAZARD OF AN ASTEROID IMPACT

http://www.boulder.swri.edu/clark/clark.html

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: http://www.boulder.swri.edu/clark/crcepsl.pdf

What Do We Know About the Impact Hazard?

How many asteroids and cometsHow many asteroids and comets there are of various sizes in Earth-approaching orbits (~1100 > 1 km diam.) So impact frequencies are known.

How much energyHow 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 consequencesenvironmental consequences.

Biosphere responseBiosphere response (agriculture, forests, human beings, ocean life) to environmental shock.

Response of human psychology, sociology, psychology, sociology, political systems, and economiespolitical systems, and economies to such a catastrophe. September 11September 11thth terrorist attack? terrorist attack?

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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 See Schweickart et al., Nov. 2003 al., Nov. 2003 Scientific AmericanScientific American

Asteroid Size Distribution: How Often Impacts of Different Energies Happen

Courtesy Al Harris

Sizes, Impact Frequencies of NEOs

DustDust

Boulder

Boulder

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Build

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MountainMountain

Second

Second

WeekWeek

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500,000 yr500,000 yr

100 Myr

100 Myr

Leonid meteor showerLeonid meteor shower

Peekskill meteoritePeekskill meteorite

Tunguska, 1908

SL9 hits

Jupiter 1994

SL9 hits

Jupiter 1994

K-T mass extinctor, 65 Myr ago

Smallest, most frequent

Smallest, most frequent

Huge, extremely rareHuge, extremely rare

15 km15 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 Tunguskas and their smaller cousins may dominate popular interest in the impact hazard, and hence the work of the NEO community.impact hazard, and hence the work of the NEO community.

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Asteroid Diameter (km) Asteroid Diameter (km)

Max

Nominal

Min

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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:

Six case studies, exemplifying the different sizes and types of impact disasters, were discussed in these terms:

a.a. Civilization destroyer: 2-3 km asteroid Civilization destroyer: 2-3 km asteroid or comet impactor comet impact

b.b. Tsunami-generator: ~200 m asteroid Tsunami-generator: ~200 m asteroid impacts in the oceanimpacts in the ocean

c.c. ~200 m asteroid strikes land~200 m asteroid strikes land

d.d. Mini-Tunguska: once-a-century Mini-Tunguska: once-a-century atmospheric explosion (30-40 m body)atmospheric explosion (30-40 m body)

e.e. Annual multi-kiloton blinding flash in Annual multi-kiloton blinding flash in the sky (4 m body)the sky (4 m body)

f.f. Prediction (or media report) of near-Prediction (or media report) of near-term impact possibilityterm impact possibility

13 January 2004: AL00667 was 13 January 2004: AL00667 was Case (f) masquerading as a Case Case (f) masquerading as a Case

(d)! Lessons must be learned(d)! Lessons must be learned. .

http://www.boulder.swri.edu/clark/oecdjanf.doc

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. 30-40 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, 2003-2004 (1 of 2)

NASA SDT report recommends Spaceguard Survey down to 140 m

Serious discussion of NEA properties and deflection practicalities Sept. 2002 NASA “Mitigation Workshop”

proceedings out by end of 2004 (Camb. Univ. Press) AIAA/B612 “Planetary Defense Conference,” Feb.

2004 on-line at: http://www.planetarydefense.info/

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, 2003-2004 (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. 2004 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. 2004 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