Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA Clark R. Chapman Southwest Research Institute Boulder, Colorado, USA “After-Banquet Talk” Longmont Astronomical Society Wayside Inn, Berthoud CO 15 January 2005 “After-Banquet Talk” Longmont Astronomical Society Wayside Inn, Berthoud CO 15 January 2005 “A Tale of Two Asteroids” To warn or not to warn…that is the question… “A Tale of Two Asteroids” To warn or not to warn…that is the question…

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…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. The Little Prince Meteorite punctured roof in Canon City, CO Global catastrophe Asteroid B s 1960s 1980s 1990s Meteor Crater

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.

They are out there, right now! The night after last year’s Longmont Astronomical Society’s banquet, my wife Y and I hosted David Levy, your speaker, at our home …and, at 3 a.m., the three of us watched the Quadrantid meteor shower Tonight, you can go out (after moonset) and look above the Pleiades (in Perseus) at Comet Machholz These are examples of “Near Earth Objects” or NEOs Photo by Gary Emerson, Coal Creek Canyon, Colorado (Dec. 31, 2004) Quadrantid bolide

Tale of the First Asteroid Tale of the First Asteroid …one year ago yesterday It was a dark and stormy night… at least it was a cloudy night over most of the world. The previous night’s CCD frames from LINEAR telescopes in New Mexico had been reduced; data were sent to the Minor Planet Center in Cambridge, Mass., and semi- automatically posted on the “NEO Confirmation Page” so that observers could find these “one night stands” again…and secure their orbits. B ut the posted ephemeris of one object (AL00667) had it brightening by 4 magnitudes in a single day! Quick calculations showed that it would strike the Earth the very next day, shortly after President Bush’s speech about US space policy. The NEO Confirmation Page Brian Marsden, MPC USAF Lincoln Lab LINEAR Observatory, New Mexico

The First Asteroid… AL00667 It was soon realized that the orbit was very uncertain, based on just 4 observations. Nevertheless, a sophisticated “Monte Carlo” statistical analysis by MPC and JPL astronomers showed that 40% of test trajectories hit Earth in the next few days. (The object seemed ~30m in size = 2MT.) Impact probability was estimated to be 10% to 25% during next 3 days, somewhere in the Northern Hemisphere. By midnight (MST), attempts to secure follow-up observations had been foiled around the world by clouds. What should NASA & IAU scientists do?

The First Asteroid… AL00667 But in Colorado the skies were clear. Amateur astronomer Brian Warner was closing up his Palmer Divide Observatory for the night when he read a late from asteroid astronomer Alan Harris…telling him that he must search for AL Warner photographed the places in the sky where AL00667 would have to be if it were to hit Earth (its “VI”)…and he found nothing. No announcement had to be made. (Whew!) Later that night, LINEAR telescopes made their own follow-up observations, confirmed the next night by Czech Republic observers. AL00667  2004 AS1: 10 times bigger but 10 times farther away…it passed by harmlessly and distantly several weeks later. Palmer Divide Observatory “VI” = Virtual Im- pactor: one of many positions where an NEA might be in the future, given the uncertainties of the “nominal” orbit.

First Asteroid… AL00667=2004 AS1 Should officials and/or the public have been notified (and when?)…had there been no more observations that night? Hindsight shows it would have been a false alarm. But suppose it had hit (maybe as Bush spoke), with no warning at all? And that seemed like a 25% chance! This was not an “error”. This was not an “error”. The observations were ambiguous. Just as it is hard to tell the difference between a bird pacing your car (which could soon fly into your windshield) and a distant airplane, flying 500 miles per hour, but appearing almost at a stationary aspect angle because it is so far away.

Tale of the Second Asteroid Tale of the Second Asteroid …2004 Christmas Holiday Threat On Wednesday evening, Dec. 22, 2004, I received an telling me that the next morning the two official NEO websites (at JPL and the Univ. of Pisa) would announce the first-ever “Torino Scale” = 2 impact warning. thousands of megatons An asteroid first discovered in June, but lost, had been rediscovered on Dec. 18 th. The combined data were very disturbing. After double-checking, this approx meter (quarter-mile) wide asteroid was calculated to have a 1-in-200 chance of striking the Earth – with a force of thousands of megatons -- on Friday, April 13, 2029.

The Second Asteroid… 2004 MN4 It would get worse, based on 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. 27 th, a discouraging 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 15 th. We now knew: 2004 MN4 would surely miss the Earth in Kitt Peak Natl. Observatory

The Second Asteroid… 2004 MN4 oooooooooooo Error “ellipse” or LOV as of 23 Dec as of 28 Dec  more observations cause “ellipse” to shrink  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 Time Moon Earth

The Second Asteroid… 2004 MN4 Observers around the world measured new positions for MN4 Searches for pre-discovery images (but unlikely because MN4 is almost always much fainter than 20 th 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 Behind the scenes, between Dec. 22 and Dec. 28:

The Second Asteroid… 2004 MN4 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. What do you think should have been done, if MN4 had hung on at TS=4 for months? There was hot debate about whether to release the possible impact points after they were calculated on Dec. 24 th. 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?

The Second Asteroid… 2004 MN4 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 wording said that the impact probability would likely go to zero soon. But some 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! Then the tsunami struck! MN4 could cause an even bigger tsunami (sobering … though 24 years away). During Christmas weekend, there were many issues: Current information: * Diameter about 300 m * Composition: ordinary chondrite * Misses by 5 Earth diams. in 2029 * 5 th mag. from Europe (evening)

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) NASA SDT proposed 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 B612 Project : see Schweickart et al., Nov Scientific American Kitt Peak Natl. Observatory

The Tsunami Reminds Us: We have Many Other Things to Worry About Source: John Pike

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