Clark R. ChapmanSouthwest Research Institute

Boulder, Colorado, USA

Clark R. ChapmanSouthwest Research Institute

Boulder, Colorado, USA

““After-Banquet Talk”After-Banquet Talk”

Longmont Astronomical SocietyLongmont Astronomical SocietyWayside Inn, Berthoud CO 15 January Wayside Inn, Berthoud CO 15 January

20052005

““After-Banquet Talk”After-Banquet Talk”

Longmont Astronomical SocietyLongmont Astronomical SocietyWayside Inn, Berthoud CO 15 January Wayside Inn, Berthoud CO 15 January

20052005

“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…

http://www.boulder.swri.edu/clark/clark.html

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 B612

1900s

1960s

1980s

1990s

Meteor Crater

Sizes and Impact Frequencies of NEOs

DustDust

Boulder

Boulder

Build

ing

Build

ing

MountainMountain

Second

Second

WeekWeek

Mill

enniu

m

Mill

enniu

m

500,000 yr500,000 yr

100 Myr

100 Myr

Leonid meteor showerLeonid meteor shower

Peekskill meteoritePeekskill meteorite

Tunguska, 1908

SL9 hits

Jupiter 1994

SL9 hits

Jupiter 1994

K-T mass extinctor, 65 Myr ago

Smallest, most frequent

Smallest, most frequent

Huge, extremely rareHuge, extremely rare

15 km15 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 These are examples of “Near Earth Objects” or NEOsEarth Objects” or NEOs

Photo by Gary Emerson, Coal Creek Canyon, Colorado (Dec. 31, 2004)

Quadrantid bolide

Tale of the First Tale of the First AsteroidAsteroid …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.

But 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, MPCBrian Marsden, MPC

USAF Lincoln Lab LINEAR Observatory, New MexicoUSAF 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 What should NASA & IAU scientists dodo??

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 e-mail from asteroid astronomer Alan Harris…telling him that he must search for AL00667.

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.

AL006672004 AS1: 10 times bigger but 10 times farther away…it passed by harmlessly and distantly several weeks later.

Palmer Divide ObservatoryPalmer 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 Tale of the Second AsteroidAsteroid …2004 Christmas Holiday Threat

On Wednesday evening, Dec. 22, 2004, I received an e-mail 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.

An asteroid first discovered in June, but lost, had been rediscovered on Dec. 18th. The combined data were very disturbing. After double-checking, this approx. 400-meter (quarter-mile) wide asteroid was calculated to have a 1-in-200 chance of striking the Earth – with a force of thousands of megatonsthousands 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. 27th, 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 15th.

We now knew: 2004 MN4 would surely miss the Earth in 2029.

Kitt Peak Natl. Observatory

The Second Asteroid…2004 MN4

o

o

o

o

o

o

Error “ellipse” or LOV as of 23 Dec. 2004 as of 28 Dec. 2004

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 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

Behind the scenes, between Dec. 22 and Dec. 28: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.

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 What do youyou think should have been think should have been done, if MN4 had hung done, if MN4 had hung on at TS=4 for months?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:During Christmas weekend, there were many issues:

Current information:Current information:

* Diameter about 300 m * Composition: ordinary chondrite * Misses by 5 Earth diams. in 2029 * 5th 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 : sB612 Project : see ee Schweickart et al., Schweickart et al., Nov. 2003 Nov. 2003 Scientific AmericanScientific American

Kitt Peak Natl. Observatory

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

Source: John Pike

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)