1. Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA “Astrobiology Societal Issues Workshop” SETI Institute, Mountain View CA Evening Panel: 9 February 2009 “Astrobiology Societal Issues Workshop” SETI Institute, Mountain View CA Evening Panel: 9 February 2009 Hazardous Near-Earth Asteroids: To Defend or Not?

2. Sizes and 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 “NEOs” = Near Earth Objects.

3. 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 (hence, 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 Response of human psychology, sociology, political systems, and economies to such a catastrophe. WE KNOW THIS… Very Well Somewhat Poorly Very Poorly

4. Impacts of Practical Concern Mass extinction events are too improbable to worry about Meteorites do minor damage, are a minuscule fraction of the hazard from “falling objects”

5. Death Threat from Impacts, by Asteroid Diameter and Location of Impact Statistical mortality rate once Spaceguard Survey is complete in a couple years Current rate (many hundreds/ year) will be down to a couple hundred per year, mainly by removing threat of “Global” impactors > 2 km diameter Dominant threat will remain for “Tunguskas,” for which there is a several-% chance this century that one will strike and kill hundreds or thousands of people. Thus Tunguskas and their smaller cousins will dominate public interest in the impact hazard. Thus Tunguskas and their smaller cousins will dominate public interest in the impact hazard. Worldwide Deaths (Annual) Asteroid Diameter (km) Tsunami Land Global (For nominal case) How the mortality will diminish from the three kinds of impacts as the Spaceguard telescopic searches continue

6. Consequences of a Large, Rare Civilization-Threatening Impact Total destruction in near-crater zone Destruction zone 30 times the size of the asteroid Tsunami (“tidal waves”) Inundation of shores of impacted ocean Stratospheric dust obscures sun Sudden global climate change threatens agriculture Widespread fires 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

7. Consequences from Small, Likely Impacts Damage & casualties are at most like a minor natural disaster (e.g. tornado, wildfire) Public and national over-reaction after 9/11 (stock market, homeland security hysteria, Iraq war) could be replicated by a modest but unexpected impact disaster. An otherwise harmless but brilliant bolide (fireball) could be mistaken for an atomic attack, causing a dangerous response. Even sensational journalism or a mistaken prediction about a possible future impact can be disruptive. OVER KASHMIR? OVER ISRAEL? HOW WOULD THE GENERALS RESPOND? “9/11”

8. The Impact Hazard in Perspective Most effects are individually familiar (fire, wind, falling debris, seismic shaking…) Disaster responders face nothing truly alien Synergy of many different effects in 1sr 10 min. versus Warning versus no warning (time and location) Deaths and injuries are dramatically reduced with warning Property damage can be lessened somewhat with warning Even with no warning, people can reduce exposure by taking cover (within seconds to minutes) if they have been educated to recognize what’s happening (Indian Ocean tsunami analogy) versus Impact disasters: local/regional versus global Like Katrina, earthquakes, or wars, unaffected people can provide emergency response… …But NOT if the consequences are global Meteorite punctured roof in Canon City, CO * Unlike most natural disasters, we can predict an NEO impact…and warn. * Unlike any other natural disaster, we can deflect the NEO, so the impact doesn’t happen.

9. The Spaceguard Survey…Now and Prospective Spaceguard Survey: 1998 to 2008, find 90% of NEAs >1 km diameter (85% complete as of 2009) Congress ordered NASA to find 90% of NEAs >140 m by 2020 Kitt Peak Natl. Observatory LINEAR, New Mexico LSST

10. Deflect an Asteroid so it Misses the Earth Most threatening NEOs are small. One can be deflected either (a) by a “Gravity Tractor” (GT) or (b) by striking it with a “kinetic impactor” (like Deep Impact), then “trimmed” by a GT If an NEO is very big or there is short warning time, only a nuclear device would be powerful enough to work Kinetic Impactor Gravity Tractor Stand-off Nuclear Blast

11. Apophis: To Tell or Not to Tell… In what was a 1-chance-in-37 that it would hit in 2029, extreme destruction would occur within a corridor near the blue line You can hardly imagine a line crossing more geopolitically sensitive, densely populated areas. But withholding information from the public violates risk- communication principles! There was hot debate about whether to release the possible impact points after they were calculated on Dec. 24 th 2004. NASA officials, scientists argued we should wait for perhaps a year. But withholding information from the public violates risk- communication principles! Population Density Apophis now has 1-in-45,000 chance of passing thru a keyhole in 2029, then striking somewhere on path-of-risk on April 13, 2036

12. Societal Issues NEO impacts: are they an Astrobiological issue? NEOs affected the origin and evolution of life on Earth NEOs currently present a “potential hazard to our home planet” NEOs could well affect the (probably distant) “future of life on Earth” Big impacts raise philosophical concerns (end of civilization) Small impacts are a largely unrecognized element of the field of “natural hazards”: public fears/perceptions, political response Deflection toolbox: Smallest NEOs: do we deflect (at great cost) or let them hit? (We can always mitigate, evacuate, undertake usual disaster response.) Largest, most dangerous, but most unlikely NEOs >1 km require nuclear technique: Do we use it? Should we even discuss it and research it? “All-hazards” approach to natural disasters should include NEOs. There’s no national or international responsibility (yet). Unusual international political, military, legal issues: being addressed by ASE input to UN (COPUOS)

13. What’s Happening Now… The National Research Council is doing a study of the NEO hazard, including detection and mitigation: the Shapiro Committee’s report is due by Dec. 2009 The Association of Space Explorers’ report “Asteroid Threats: A Call for Global Response” will be presented to the United Nations (COPUOS) later this month concerning protocols and a management structure for an international approach to the NEO impact hazard The next Planetary Defense Conference (sponsored by the International Academy of Astronautics) will be in Granada, Spain, 27- 30 April 2009

14. 433 Eros Comet McNaught

15. Numbers of Small NEOs Known and to be Discovered The discovery rate for 10 m NEAs may go up 2000 times! By the end of SG2, we will know nearly half of Tunguska-class NEAs. We will then be tracking 2 million 30 m objects; any threatening one will demand attention, even if impact damage might be minimal. Think of the implications for meteoroids research: a quarter-million known objects 5 m in size! H Diam. (km) Known Now SG1 (goal) SG2 (goal) No. % of Tot. No. % of Tot. No. % of Tot. 17.75 1.0 234 59 280 83 333 98 22.02 0.14 162 3.5 450 9 4000 83 24.26 0.05 147 0.09 1200 0.6 80000 40 25.36 0.03 85 0.01 640 0.08 2 million 20 27.75 0.01 17 1e(-6) 200 1e(-5) 400000 2 29.26 0.005 6 3e(-8) 30 3e(-7) 200000 0.2 Data courtesy A. Harris (June 2007) Incremental numbers: 0.5 mag. Intervals centered on listed mag. and size.

16. How Important is NEO Threat? We’ve Many Other Things to Worry About! Source: John Pike NEO impact similar to this 9/11 Mortality from Twentieth Century Catastrophes

17. Public Perception An impact disaster has never been experienced in recorded history. The tiny chances combined with huge consequences are difficult for people to comprehend (e.g. building in floodplains…or hoping to win the lottery). The impact hazard is “dreadful” and “apocalyptic”…hence people may over-react. Scientific/mathematical illiteracy prevails. Odds of a “Royal Flush” (1 in 649,739) are like chances of a 1.5 km-wide asteroid striking next year! You’re kidding! I was struck twice by lightning, too!

18. How Well do we Plan for and Respond to Other Disasters? Guatemala, Hurricane Stan Indian Ocean Tsunami Kashmir Earthquake Hurricane Katrina

19. Comparing NEO Impacts and Climate Change NEO Impact Similarities… They can potentially affect the globe They can potentially affect the globe Asteroids can be deflected to miss Earth Asteroids can be deflected to miss EarthDissimilarities… Global effects within 2 hours, global climate change within months Global effects within 2 hours, global climate change within months Extremely unlikely to happen this century Extremely unlikely to happen this century Climate Change Similarities… Global warming is planetary in scale Global warming is planetary in scale Society can reduce greenhouse gases Society can reduce greenhouse gasesDissimilarities… Timescale for major changes: about one century Timescale for major changes: about one century Actually underway right now Actually underway right now

20. Will an NEO Destroy our World? The NEO hazard helps us contemplate the most extreme environmental disaster and put the lesser, more likely ones into context… …and to distinguish between societal issues and true catastrophes. Many threats to society and our lives (flu, war, famine…even global warming) are here today. Asteroids are in our future…as places to travel to, as fuel stations for a spacefaring civilization. Alabama, 1954 Asteroid Eros (Pat Rawlings, SAIC) Asteroid Itokawa Arecibo radar

21. The Torino Scale (to communicate seriousness of predicted NEO impacts) Astronomers tried to learn from other risk communicators and developed a color-coded scale. Official scale: the words (for TS = 0 – 10, 1 dimension) TS is a simplification of the Palermo Scale, based on energy, probability, how far in future (3 dimensions). Designed pedagogically to illustrate unlikelihood of catastrophe: nearly all cases would be TS=0 or TS=1. Adopted by IAU in 1999, used by most news media. Homeland Security Terrorism scale became a joke. Behind-the-scenes arguments about T.S., but it’s OK. Then in Dec. 2004 Apophis blew it away: TS = 4!

22. Chances of Dying from Selected Causes (for U.S.A.) (Chapman/Morrison 1994) By terrorism (much due to Sept. 11th) 9/11 Reduced risk thanks to Spaceguard since 1998