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

1. http://www.boulder.swri.edu/clark/clark.html Apophis in 2036: Thinking About a Possible Asteroid Impact Catastrophe Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA Luncheon Talk CU Sigma Xi Skaggs Research Center, NIST/NOAA Boulder CO 7 February 2006

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…Halley’s Comet, end-of-world 1910 • 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. Sizes and Impact Frequencies of NEOs Leonid meteor shower Smallest, most frequent “NEOs” = Near Earth Objects. 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

4. 2004 MN4 (aka “Apophis”): Christmas Holiday Threat • On Wednesday evening, Dec. 22, 2004, I received an e-mail saying that tomorrow the two official NEO websites (JPL, Univ. of Pisa) would announce the first-ever “Torino Scale” = 2 impact warning. • An NEO discovered in June, but lost, had been rediscovered on Dec. 18th. The combined data were disturbing. After double-checking, this ~400-meter (1/4-mile) wide asteroid was calculated to have a 1-in-200 chance of striking Earth – with a force of thousands of megatons – on Friday, April 13, 2029.

5. The Threat Grows, then Vanishes • It would get worse, based on telescopic observations on succeeding nights: • from 1 chance in 200 on Dec. 22, it would go: • to 1 chance in 170 on Dec. 23, • to 1 chance in 60 on Dec. 24 ( TS=4!), • to 1 chance in 40 on Christmas Day, Dec. 25, • to 1 chance in 37 on Dec. 27, and – based on the next night’s data -- would have gone • to 1 chance in 20 on Dec. 28, except that: • On Dec. 27th, an against-the-odds search for pre-discovery observations of MN4 had an unexpected success: • Marginal, missed, faint images were found on CCD images from the Spacewatch telescope on March 15th. • We now knew (or did we???): 2004 MN4 would surely miss the Earth in 2029. Kitt Peak Natl. Observatory

6. Why the Threat Grew, Vanished Error “ellipse” or LOV as of 23 Dec. 2004 as of 28 Dec. 2004 o o o o o o Probability of impact (ratio of Earth diameter to length of line) grows as line shrinks, then suddenly goes to zero when right-hand end of line moves to the left of the Earth Moon Earth  more observations cause “ellipse” to shrink  Time

7. Astronomers Work During the Holidays Behind the scenes, Dec. 22 through Dec. 28: • Observers around the world measure new positions for MN4 • Searches for pre-discovery images (but unlikely because MN4 is almost always much fainter than 20th magnitude) • Arecibo radar scheduled for late Jan. 2005, when MN4 is north • Observations planned to refine size and composition of MN4 • Calculations of where MN4 might hit on the Earth in 2029 • Statements prepared, questions from news media answered

8. To Tell or Not to Tell… • In the 1-chance-in-38 that it would hit, extreme destruction would occur within the zone between the dashed lines, somewhere along the solid red line. • You can hardly imagine a line cross- ing more densely populated areas. There was hot debate about whether to release the possible impact points after they were calculated on Dec. 24th. Some argued we should wait for perhaps a year. What do you think should have been done, if MN4 had hung on at TS=4 for months?

9. Immediate, Urgent Issues (as of Christmas 2004) During Christmas weekend, there were many issues: • How big is MN4? It could be anywhere from 200 meters across to 1.5 kilometers! (If >700 m, it would be TS=5; if >1 km, TS=7!) • Crazy stuff was on the internet. Should we issue press releases or remain quiet? • The official TS wording said that the impact probability would likely go to zero soon. But some experts believed that it might stay at TS=4 for many weeks or months. • Does NASA lose trust by “crying wolf” or by keeping silent about facts of potentially high interest? • Then the tsunami struck! MN4 could cause an even bigger tsunami (sobering … though 24 years away). Info as of mid-January 2005: * Diameter about 300 m * Composition: ordinary chondrite * Misses by 5 Earth diams. in 2029 * 5th mag. from Europe (in 2029)

10. Then Things Changed Again! • Arecibo radar discovers that MN4 will pass twice as close to Earth in 2029! • Under the height of communications satellites! • It will sail across European skies as a bright star! • 1-in-1000-year event! (???) • MN4 could pass through a “keyhole” that would result in Earth impact later in the 2030’s • Gravitational tides could physically alter the asteroid

11. Impact on Apr. 13th, 2036? • Chances currently rated 1-in-3500 to 1-in-6200 • Must pass through keyhole few hundred meters wide • The B612 “gravity tractor” scheme could move it away from keyhole, if we get started soon enough • Radar possibility in few months could refine orbit so that 2036 threat vanishes • Then Apophis is invisible for ~6 years • If threat remains after 2013, we could send a transponder mission before 2020 • If threat still remains, send gravity tractor to push in mid-2020’s

12. Where it Could Hit…Gravity Tractor to the Rescue! Artwork by Dan Durda Scientist/ astronaut Ed Lu From Lu & Love, Nature, 2005

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

14. 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) • Congress just ordered 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

15. Practicalities, Perceptions, and Politics LINEAR, New Mexico • The Spaceguard Survey is 2/3rds complete for >1 km asteroids • Congress has mandated, but not funded, search for NEOs >140 meter diameter • B612 nuclear-electric powered propulsion favorably evaluated by NASA • But NEP put on back-burner: budget cuts • Other push-asteroid technologies • No national or international agency takes responsibility for evaluating and planning for an NEO disaster • Many “studies” but little integration into “all-hazards” field of emergency planning and response or policy development • No funding except for Spaceguard

16. How Important is NEO Threat? We have Many Other Things to Worry About! Source: John Pike Source: John Pike

17. But Rocks do Hit People… and Consider the Dinosaurs Alabama, 1954 • 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? (Pat Rawlings, SAIC) Asteroid Eros