Predicting and Comprehending Predicting and Comprehending Asteroid Impacts Asteroid Impacts Fertile Ground for Fertile Ground for Applications of Statistics Applications of Statistics Clark R. Chapman Clark R. Chapman Southwest Research Inst. Southwest Research Inst. Boulder, Colorado, USA Boulder, Colorado, USA Invited Session: Prediction of Invited Session: Prediction of Catastrophic Events Catastrophic Events “Interface 2003 Interface 2003” ”: 35th Symposium on the : 35th Symposium on the “ “Interface 2003”: 35th Symposium on the Interface: Computing Science & Statistics Interface: Computing Science & Statistics Interface: Computing Science & Statistics Salt Lake City, Utah 15 March 2003 Salt Lake City, Utah 15 March 2003 Salt Lake City, Utah 15 March 2003
Comets and Asteroids The processes that formed the planets 4.6 The processes that formed the planets 4.6 billion years ago left many small remnant billion years ago left many small remnant objects: comets (beyond the outer planets) and objects: comets (beyond the outer planets) and asteroids (in a “belt” between the orbits of Mars asteroids (in a “belt” between the orbits of Mars and Jupiter). Some of them occasionally cross and Jupiter). Some of them occasionally cross the Earth’s orbit and can strike our planet... if it the Earth’s orbit and can strike our planet... if it Comets Comets happens to be there at the same time. happens to be there at the same time. Jupiter’s orbit Asteroid Belt We are We are Here! Here! Sun NEOs Comets come from far beyond Jupiter Two asteroids Two asteroids colliding colliding
The Hazard from Asteroids and Comets: Overview The Little Prince � The Earth encounters interplanetary projectiles, ranging: (a) tiny, harmless ones; (b) gigantic, destructive ones… (and everything in between). � The most dangerous ones are very rare but very destructive. Smaller impacts, with greater chances of happening soon, also merit practical concern by relevant public Meteorite punctured roof in Canon City, CO officials. Global catastrophe � This extreme example of a natural disaster (tiny chances of happening, but with huge consequences) challenges a rational response by citizens and policy-makers.
Sizes, Impact Frequencies of NEOs Leonid meteor Leonid meteor Smallest, most Smallest, most shower shower frequent frequent d d n n Week Week o o Boulder c Boulder c e e t t s S s S u u D Peekskill meteorite D Peekskill meteorite Huge, Huge, extremely rare extremely rare 100 Myr 100 Myr 1 g 1 g n n 5 5 Millenniunm Millenniunm i i d d k k l l i i K-T mass extinctor, 65 Myr ago m u u m Tunguska, 1908 B B M M o o u u n n t a t a i i n n 500,000 yr 500,000 yr SL9 SL9 hits hits Jupiter Jupiter 1994 1994
What Do We Know About the ! s i h t o t Impact Hazard? k c a b g n i m o c e b l l ’ I � How many asteroids and comets there are of Very Poorly Somewhat Very Well Very Well various sizes in Earth-approaching orbits (hence, impact frequencies are known). � How much energy is delivered by an impact (e.g. WE KNOW THIS… 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.
Potential Impacts of Practical Concern OBJECT IMPACT CHANCE CHARACTER OF DAMAGE DIAM. ENERGY PER 100 YR >3 km 1.5 mil. MT 1 in 50,000 Global climate disaster, most killed, civilization destroyed >1 km 80,000 MT 0.02% Devastation of large region or an entire ocean rim >300 m 2,000 MT 0.2% 5 km crater; huge tsunami or destruction of small nation >100 m 80 MT 1% Exceeds greatest H-bomb; 1 km crater; locally devastating >30 m 2 MT 40% Stratospheric explosion; damage within tens of km >10 m 100 kT 6 per century Broken windows, little serious damage on ground >3 m 2 kT 2 per year Blinding flash, could be mistaken for atomic bomb
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 OVER KASHMIR? OVER ISRAEL? HOW WOULD THE GENERALS RESPOND? years) � Media hype, false alarm (happens every few months)
Risk vs. Scale of Impact � Annual fatalities peak for events near the global “threshold size”, t s u D about 2 km c i r e Tsunami � Orange/yellow h p s o zone illustrates t a r t our range of S uncertainties for agricultural disaster due to stratospheric dust � Tsunamic risk very uncertain
What Can We Do about This? 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 (Spaceguard Survey) � 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.)
How Does a Scientifically Illiterate Public React to Asteroids? Here’s a case of very low statistical Here’s a case of very low statistical odds, but the potential catastrophe odds, but the potential catastrophe could destroy civilization... could destroy civilization...
Asteroid Impacts are “Chancy” Public Education about Probabilities Public Education about Probabilities We’re all familiar with people who think they We’re all familiar with people who think they will win the lottery, who build homes on the will win the lottery, who build homes on the 100 100-year floodplain because last year’s flood year floodplain because last year’s flood was was the 100 the 100-year flood according to the Army year flood according to the Army Corps of Engineers…and so on. This is Corps of Engineers…and so on. This is not not encourtaging about the possibility for rational encourtaging about the possibility for rational thinking about asteroids! thinking about asteroids!
A Royal Flush (2003 UPDATE: This (2003 UPDATE: This statistic has changed in the statistic has changed in the last few years as we have last few years as we have discovered most of the mile- discovered most of the mile- wide asteroids and learned wide asteroids and learned that those won’t strike Earth that those won’t strike Earth this century: now there’s a this century: now there’s a slightly better chance of slightly better chance of getting a Royal Flush than getting a Royal Flush than death-by-asteroid next year! ) death-by-asteroid next year! ) Odds: 1 to 649,739 � It is more likely that a mile � It is more likely that a mile- -wide asteroid will wide asteroid will strike Earth next year than that the strike Earth next year than that the next poker next poker hand you are dealt will be a royal flush. hand you are dealt will be a royal flush.
Chances from Dying from Selected Causes (for U.S.A.) By terrorism (mostly due to Sept. 11th attacks)
20th Century Catastrophes: We have much more to worry about than impacts! This is what we have to (Asteroids similar) worry about this month Source: John Pike � Averaged over long durations, the death rate expected from impacts is similar to that from volcanoes.
Fatality Rates Compared with Accidents and Natural Hazards
This Week is the Fifth Anniversary of the Scare The “Scary” Case of 1997 XF11 In March 1998, head- � lines warned of pos- 10 10 sible impact in 2028. The next day, old data � ruled it out…but the 5 5 prediction was badly (100000 km) (100000 km) mistaken. 0 0 -5 5 - -10 10 - -15 15 - -15 - 15 -10 - 10 -5 - 5 0 0 5 5 10 10 15 15 (100000 km) (100000 km)
1997 XF11 Error “Ellipse” Original “back Original “back-of of-the the- envelope” calculation reported envelope” calculation reported in a Press Statement by the in a Press Statement by the Minor Planet Center at Harvard Minor Planet Center at Harvard Part of very elongated error ellipse Actual Monte Carlo calculations Actual Monte Carlo calculations of very elongated error ellipse, of very elongated error ellipse, done by Muinonen from same done by Muinonen from same data available to Minor Planet data available to Minor Planet Earth Center (it took several days of Center (it took several days of computer time) computer time)
1997 XF11 Error Ellipse: Details
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