Clark R. Chapman, Ph.D.Clark R. Chapman, Ph.D. Institute Scientist Institute ScientistDepartment of Space StudiesDepartment of Space Studies (Boulder, Colorado) (Boulder, Colorado)

Southwest Research InstituteSouthwest Research Institute

Clark R. Chapman, Ph.D.Clark R. Chapman, Ph.D. Institute Scientist Institute ScientistDepartment of Space StudiesDepartment of Space Studies (Boulder, Colorado) (Boulder, Colorado)

Southwest Research InstituteSouthwest Research Institute

NEAR-Shoemaker’s Exploration of Eros & the Impact Hazard

NEAR-Shoemaker’s Exploration of Eros & the Impact Hazard

Invited Presentation (on behalf of Don Yeomans and Invited Presentation (on behalf of Don Yeomans and David Morrison) to the ATWG Conference, Lockheed David Morrison) to the ATWG Conference, Lockheed Martin, 15 May 2001, Highlands Ranch, ColoradoMartin, 15 May 2001, Highlands Ranch, Colorado

Invited Presentation (on behalf of Don Yeomans and Invited Presentation (on behalf of Don Yeomans and David Morrison) to the ATWG Conference, Lockheed David Morrison) to the ATWG Conference, Lockheed Martin, 15 May 2001, Highlands Ranch, ColoradoMartin, 15 May 2001, Highlands Ranch, Colorado

The Hazard from Asteroids and Comets

Each year, there is a 1-in-300,000 chance that a Each year, there is a 1-in-300,000 chance that a mile-wide asteroid or comet will strike the Earth.mile-wide asteroid or comet will strike the Earth.

Less than 50 percent of the objects threatening Less than 50 percent of the objects threatening Earth have been found. Those that remain could Earth have been found. Those that remain could strike without warning.strike without warning.

This extreme example of a natural disaster (a tiny This extreme example of a natural disaster (a tiny probability, but with huge consequences) probability, but with huge consequences) challenges a rational policy response. challenges a rational policy response.

Early asteroid-like “planetessimals” formed the Early asteroid-like “planetessimals” formed the inner planets and the cores of the outer planets.inner planets and the cores of the outer planets.

Tunguska in Perspective

Impact of Fragment K of Comet Shoemaker-Levy on Jupiter

The scars of three The scars of three previous impacts previous impacts can be seen on the can be seen on the planetary disk.planetary disk.

Image from Peter McGregor and Mark Allen, Image from Peter McGregor and Mark Allen, ANU 2.3m telescope.ANU 2.3m telescope.

What Do We Know About This Hazard?

How many asteroids and comets there are of How many asteroids and comets there are of various sizes in Earth-approaching orbits various sizes in Earth-approaching orbits (hence, impact frequencies are known).(hence, impact frequencies are known).

How much energy is delivered by impact How much energy is delivered by impact (such as the TNT equivalence, size of (such as the TNT equivalence, size of resulting crater).resulting crater).

How much dust is raised into the stratosphere How much dust is raised into the stratosphere and other environmental consequences.and other environmental consequences.

Biosphere response (agriculture, forests, Biosphere response (agriculture, forests, humans, ocean life) to environmental shock.humans, ocean life) to environmental shock.

Response of human psychology, sociology, Response of human psychology, sociology, political systems, and economies to such a political systems, and economies to such a catastrophe.catastrophe.

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Classification of Hazards

High Altitude DisintegrationHigh Altitude Disintegration Projectile fragments and disperses at high altitudes (over 40 km)Projectile fragments and disperses at high altitudes (over 40 km) Negligible surface damageNegligible surface damage

Local Effects (Blast Damage)Local Effects (Blast Damage) Projectile explodes in lower atmosphere or craters surfaceProjectile explodes in lower atmosphere or craters surface Severe localized damage from blastSevere localized damage from blast

Global Effects (Environmental Degradation)Global Effects (Environmental Degradation) Short-term global scale climatic changes (such as impact winter)Short-term global scale climatic changes (such as impact winter) Global loss of food crops leads to large-scale famine, disease, and Global loss of food crops leads to large-scale famine, disease, and

possible breakdown of civilizationpossible breakdown of civilization

Mass Extinction (Environmental Catastrophe)Mass Extinction (Environmental Catastrophe) Global environmental damage on a large scale (such as K/T event)Global environmental damage on a large scale (such as K/T event)

Mass extinction (many species lost forever; nearly all humans Mass extinction (many species lost forever; nearly all humans die)die)

Chief Environmental Consequences of Impacts

Is Civilization Robust or Fragile?

Arguments for FragilityArguments for Fragility Modern people are disconnected from nature, Modern people are disconnected from nature,

survivabilitysurvivability Technology is ever more specializedTechnology is ever more specialized People are interdependent on distant resources, other People are interdependent on distant resources, other

nationsnations If societal breakdown spawns violence, modern If societal breakdown spawns violence, modern

weaponry is very dangerousweaponry is very dangerous   Arguments for RobustnessArguments for Robustness

Technological refugia exist (such as bomb shelters)Technological refugia exist (such as bomb shelters) Society has become experienced in disaster recoverySociety has become experienced in disaster recovery Technological know-how has become pervasiveTechnological know-how has become pervasive Historical precedence; recovery from WWII was rapid Historical precedence; recovery from WWII was rapid

Risk vs. Scale of Impact

A Royal Flush

It is more likely that a mile-wide asteroid will strike It is more likely that a mile-wide asteroid will strike Earth next year than the next poker hand you are Earth next year than the next poker hand you are dealt will be a royal flush.dealt will be a royal flush.

Odds:Odds:1 to 649,7391 to 649,739

20th Century Catastrophes

Averaged over long durations, the death rate expected Averaged over long durations, the death rate expected from impacts is similar to that from volcanoes.from impacts is similar to that from volcanoes.

Source: John Pike

Chances from Dying from Selected Causes

Mitigation Options

Spaceguard SurveySpaceguard Survey

90 percent of potentially hazardous asteroids could be 90 percent of potentially hazardous asteroids could be found telescopically within a decade; certified as safe.found telescopically within a decade; certified as safe.

Deflect by Stand-off Neutron Bomb BlastDeflect by Stand-off Neutron Bomb Blast

Spacecraft and bomb technologies exist and need to Spacecraft and bomb technologies exist and need to be integrated and deployed, unless a threatening be integrated and deployed, unless a threatening object were found, due to the long lead-time.object were found, due to the long lead-time.

Standard Hazard MitigationStandard Hazard Mitigation

Extrapolate civil defense, natural hazard precautions Extrapolate civil defense, natural hazard precautions from local to world context.from local to world context.

tan = mv/mvorbit

Miss distance > 10 x Earth Radius

If deflection occurs at 1 AU from Earththe necessary impluse is mvtan = 0.0004 mvorbit

Typically vorbit 20 km/s and v 8 m/s

Required deflection velocity Required deflection velocity as a function of time before as a function of time before impact.impact.

Required impulse as a function of Required impulse as a function of time before impact. Shown are capa-time before impact. Shown are capa-bilities of the Space Shuttle’s main bilities of the Space Shuttle’s main engines, the 1engines, the 1stst stage of the Delta II, stage of the Delta II, and the NEAR spacecraft.and the NEAR spacecraft.

Densities of Craters and Boulders on Eros vs. Size

Small-Scale Features: Why?

There are boulders, blocks, even “ponds” but There are boulders, blocks, even “ponds” but no thick lunar-like regolithno thick lunar-like regolith

Eros Eros mustmust be different from Moon, with be different from Moon, with widespread ejecta, even net erosion (lunar widespread ejecta, even net erosion (lunar regolith is churned in place)regolith is churned in place)

Blocks are ejecta from big craters and/or Blocks are ejecta from big craters and/or derived derived in situin situ but not readily destroyed but not readily destroyed

J. Bell (Univ. Hawaii) invokes Yarkovsky Effect J. Bell (Univ. Hawaii) invokes Yarkovsky Effect to deplete small asteroidal projectiles, hence to deplete small asteroidal projectiles, hence few craters, blocks are preservedfew craters, blocks are preserved

That’s That’s partpart of the story…plus seismic shaking, of the story…plus seismic shaking, inhibited crater production by blocks, etc.inhibited crater production by blocks, etc.

Other Eros Results from NEAR-Shoemaker

Bulk density ~2.7 g/cc Bulk density ~2.7 g/cc (rocky but with some (rocky but with some voids), uniformvoids), uniform

Bulk chemistry (from X-ray) Bulk chemistry (from X-ray) similar to ordinary similar to ordinary chondrites (calibrations are chondrites (calibrations are ongoing); consistent with ongoing); consistent with infrared resultsinfrared results

Global ridge structures Global ridge structures imply that Eros is an intact-imply that Eros is an intact-but-shattered fragment of but-shattered fragment of its parent body, not a its parent body, not a “rubble pile”“rubble pile”

IR spectral band positions imply ordinary chondrite

Headline: Mile-Wide Asteroid Will Hit in 2028

Which is least likely to be correct?Which is least likely to be correct?

A.A. The news report is wrong due to badThe news report is wrong due to badjournalism.journalism.

B.B. The scientific forecaster goofed. We’re safe.The scientific forecaster goofed. We’re safe.

C.C. The astronomers erred. The asteroid is tiny;The astronomers erred. The asteroid is tiny;most of the world is safe.most of the world is safe.

D.D. An asteroid will hit Earth in 2028.An asteroid will hit Earth in 2028.

The correct answer is D:The correct answer is D:

A, B, and C are all much more likely to explain the A, B, and C are all much more likely to explain the headline.headline.

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Prediction is the Event

Scientists who predict think of predictions as dry Scientists who predict think of predictions as dry scientific results, with objective error-bars.scientific results, with objective error-bars.

Users of such predictions are mobilized into action by Users of such predictions are mobilized into action by the prediction.the prediction.

The predicted event may not happen as predicted; it The predicted event may not happen as predicted; it may or may not have consequences. The predictions may or may not have consequences. The predictions always have consequences.always have consequences.

Predictions of emotionally laden disasters result in Predictions of emotionally laden disasters result in subjective, sometimes irrational responses.subjective, sometimes irrational responses.

Predictions must be made with social responsibility, Predictions must be made with social responsibility, whether of a potential terrorist operation or of an whether of a potential terrorist operation or of an asteroid impact.asteroid impact.

Because of Uncertainties, Future Impact Scares are Likely

There is about a 5 percent chance an object over 1 km There is about a 5 percent chance an object over 1 km will pass close to Earth during the 21st century.will pass close to Earth during the 21st century.

Twice a decade, a Tungusta-sized object passes Twice a decade, a Tungusta-sized object passes within that same distance.within that same distance.

Astronomers might call these “safe” encounters, but Astronomers might call these “safe” encounters, but would politicians and military leaders take such a would politicians and military leaders take such a dispassionate view?dispassionate view?

Uncertainty biases in asteroid albedoes and sizes Uncertainty biases in asteroid albedoes and sizes trend toward overestimated sizing of newly found trend toward overestimated sizing of newly found objects; expect exaggerated early reports.objects; expect exaggerated early reports.

Future impact scares will happen, even if mistakes are Future impact scares will happen, even if mistakes are reduced. The unlikely, real disaster may be lost in the reduced. The unlikely, real disaster may be lost in the noise of false alarms.noise of false alarms.

When an Impact Can’t Be Ruled Out, Then What?

Rate of NEO discovery is rapidly increasing, Rate of NEO discovery is rapidly increasing, so “near misses” will become common.so “near misses” will become common.

Approximate orbits can be calculated within Approximate orbits can be calculated within days; accurate orbits take two or more years.days; accurate orbits take two or more years.

During this interval, some asteroids will During this interval, some asteroids will seem targeted to hit Earth before orbits can seem targeted to hit Earth before orbits can be improved.be improved.

““Cry wolf” announcements can be expected Cry wolf” announcements can be expected from reputable astronomers, but public from reputable astronomers, but public officials, the military, and the public are officials, the military, and the public are unprepared to know how to react.unprepared to know how to react.

The Torino Scale

Criticism: Richter Scale; the scale changes Criticism: Richter Scale; the scale changes

Answer: Many geological, meteorological, and Answer: Many geological, meteorological, and space physics scales change as forecasts change.space physics scales change as forecasts change.

Criticism: Scientific complexity is oversimplified.Criticism: Scientific complexity is oversimplified.

Answer: For public, keep it simple.Answer: For public, keep it simple.

Criticism: Who needs it?Criticism: Who needs it?

Answer: Pedagogical tool for science journalists Answer: Pedagogical tool for science journalists and teachers.and teachers.

This 1-to-10 one-dimensional scale adopted by the This 1-to-10 one-dimensional scale adopted by the International Astronomical Union provides a simple International Astronomical Union provides a simple description to the public of the level of hazard posed by description to the public of the level of hazard posed by a newly discovered, potentially threatening asteroid.a newly discovered, potentially threatening asteroid.

The Torino Scale

Events Having No Events Having No Likely ConsequencesLikely Consequences

Events MeritingEvents MeritingCareful MonitoringCareful Monitoring

Events MeritingEvents MeritingConcernConcern

ThreateningThreateningEventsEvents

CertainCertainCollisionsCollisions

The Torino Scale

Results from SwRI Internal Research

Completed and published a chapter in Prediction.Completed and published a chapter in Prediction.

Participated in the Torino IMPACT workshop, June 1999.Participated in the Torino IMPACT workshop, June 1999.

Collaborated with science writers in helping Prof. R. Binzel Collaborated with science writers in helping Prof. R. Binzel (MIT) develop the Torino Scale for public understanding of (MIT) develop the Torino Scale for public understanding of impact risk.impact risk.

Spoke at the High Consequence Systems Surety Symposium at Spoke at the High Consequence Systems Surety Symposium at Sandia National Laboratory, November 1999.Sandia National Laboratory, November 1999.

Prepared invited review and paper for the Conference on Prepared invited review and paper for the Conference on Catastrophic Events and Mass Extinctions: Impacts and Catastrophic Events and Mass Extinctions: Impacts and Beyond in Vienna, July 2000.Beyond in Vienna, July 2000.

Prepared SwRI white paper on the impact hazard, which served Prepared SwRI white paper on the impact hazard, which served as a basis for the recent AIAA/UN Workshop on International as a basis for the recent AIAA/UN Workshop on International Cooperation in Space in Seville, Spain, March 2001.Cooperation in Space in Seville, Spain, March 2001.

Findings: Detection and Impact Effects

About 50 percent of an estimated 1,000 near-Earth asteroids About 50 percent of an estimated 1,000 near-Earth asteroids over 1 km diameter have been found.over 1 km diameter have been found.

Last 10 percent will be more difficult to find, especially those Last 10 percent will be more difficult to find, especially those mostly interior to the Earth’s orbit.mostly interior to the Earth’s orbit.

Near-Earth asteroids smaller than 1 km are being sampled, Near-Earth asteroids smaller than 1 km are being sampled, but most will remain undiscovered.but most will remain undiscovered.

Long-period comets present a nearly intractable problem and Long-period comets present a nearly intractable problem and may constitute a significant part of the hazard.may constitute a significant part of the hazard.

Ground-based searches could be augmented by space-based Ground-based searches could be augmented by space-based searches.searches.

Analyses of environmental stages are rather crude.Analyses of environmental stages are rather crude.

So far, there is very little modeling of possible and social So far, there is very little modeling of possible and social consequences. consequences.

Findings: Evaluation, Warning, and Mitigation

Existing structure is disorganized: Astronomers are just Existing structure is disorganized: Astronomers are just starting to learn how to communicate, but no relevant starting to learn how to communicate, but no relevant agencies are prepared to listen and act.agencies are prepared to listen and act.

Asteroid deflection scenarios have been conceived, but no Asteroid deflection scenarios have been conceived, but no serious systems engineering or planning has been done to serious systems engineering or planning has been done to deal with various possible cases.deal with various possible cases.

No known consideration by civil defense and disaster No known consideration by civil defense and disaster management agencies, let alone any assignment of management agencies, let alone any assignment of responsibilities to scientific agencies.responsibilities to scientific agencies.

No government or formal scientific advisory body has No government or formal scientific advisory body has established the level of priority the impact hazard should established the level of priority the impact hazard should command with respect to other national priorities.command with respect to other national priorities.

Recommendations

More public education about impact hazard; public officials More public education about impact hazard; public officials need to be brought up to speed.need to be brought up to speed.

Formal notification protocols need to be implemented Formal notification protocols need to be implemented concerning predicted potential impacts.concerning predicted potential impacts.

Connections must be made with national emergency Connections must be made with national emergency management agencies and analogous international agencies.management agencies and analogous international agencies.

Torino Scale needs to be clarified and utilized.Torino Scale needs to be clarified and utilized.

Systems studies needed on proper mix of approaches to Systems studies needed on proper mix of approaches to extend the Spaceguard Survey.extend the Spaceguard Survey.

Research is needed on how to couple deflection technologies Research is needed on how to couple deflection technologies to asteroids, how to avoid disruptions, and more.to asteroids, how to avoid disruptions, and more.

Conclusion

Humans have the intelligence and capability to Humans have the intelligence and capability to protect our civilization from this threat from the protect our civilization from this threat from the skies.skies.

The dinosaurs failed.The dinosaurs failed.

Is society going to gamble and submit to fate or Is society going to gamble and submit to fate or will it undertake a measured, rational response?will it undertake a measured, rational response?

Society must educate its leaders and public Society must educate its leaders and public officials to the facts of the impact hazard, decide officials to the facts of the impact hazard, decide what should be done, then do it. what should be done, then do it.