Clark R. ChapmanSouthwest Research Institute

Boulder, Colorado, USA

Clark R. ChapmanSouthwest Research Institute

Boulder, Colorado, USA

Near-Earth Objects Hazard:Near-Earth Objects Hazard:Knowledge and ActionKnowledge and Action

Belgirate, ItalyBelgirate, Italy26-28 April 200626-28 April 2006

Near-Earth Objects Hazard:Near-Earth Objects Hazard:Knowledge and ActionKnowledge and Action

Belgirate, ItalyBelgirate, Italy26-28 April 200626-28 April 2006

The Case of Apophis: Lessons LearnedThe Case of Apophis: Lessons Learned

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

How Well do we Plan for and Respond to Disasters?

Guatemala, Hurricane Stan

Indian Ocean Tsunami Kashmir Earthquake

Hurricane Katrina

My Context for Considering Apophis

Asteroid astronomers and space agencies as “risk communicators” and “disaster managers”: we must do better!

How did the Apophis story unfold as witnessed by the attentive public?

What attributes of the Apophis story provide guidance about how to handle future cases, especially given the near-term increase in discovery rate expected from Pan-STARRS?

How important is the existing threat from Apophis? What should we be doing?

Now, let us begin the narrative of “MN4”…Now, let us begin the narrative of “MN4”…

Discovery of 2004 MN4

15 March 2004: faint images recorded by Spacewatch but too faint to be automatically detected.

19 & 20 June 2004: Tucker, Tholen et al., Kitt Peak Obs. Not discovered as part of a regular Spaceguard Program;

impossible to assign reliable errors to experimental astrometry

Then lost.

18 December 2004: recovery by Garradd, Siding Springs Poor statistics for this observatory, too

20 December 2004: With 1.7-day arc, JPL Sentry predicts 1-in-5000 chance of impact on 13 April 2029

21-22 December: Tholen reanalyzes June data, new observations are reported: 1-in-250 chance of impact!

2004 MN4:2004 MN4: Christmas Holiday Threat

22 December 2004: Email sent by Yeomans to 25 astronomers says that the next day JPL and NEODyS will announce the first-ever Torino Scale = 2 impact warning.

23 December 2004: Similar statements issued by JPL & NEODyS report that this ~460-meter wide asteroid, nominally flying by at twice the lunar distance, has 1-in-170 chance of striking Earth – with a force of thousands of megatonsthousands of megatons – on Friday, 13 April 2029.

News media initially mostly inattentive due to Christmas (also Benny was on holiday)

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 March 15th CCD images from the Spacewatch telescope.

We now knew (or did we???): 2004 MN4 would surely miss the Earth in 2029.

Kitt Peak Natl. Observatory

Path on TS diagram, with albedo/size error bar

Why the Threat Grew, Vanished(not intuitive, especially to public)

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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

Astronomers Work During the Holidays

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 mag. and/or near Sun)

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, 22 through 28 Dec. 2004:Behind the scenes, 22 through 28 Dec. 2004:

“Path of Risk”: To Tell or Not to Tell…

In the 1-chance-in-37 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?

Population Density

Risk Management Experts Say: Put it all Out There

Covello’s (1988) 4th Cardinal Rule for Risk Communication to Build Trust and Credibility: “Be honest, frank, and open. Disclose risk info ASAP; if in doubt, lean toward sharing more info, not less.”

Regarding the tension between providing accurate info and providing it quickly: to wait for all info to be complete and verified before release “can create an info vacuum that will be filled with rumor and speculation” (US Dept HHS R.C. Guidelines, 2002).

Sandman’s (2003, US CDC) bad reasons for delaying information: “The information hasn’t been quality controlled yet” “People will misunderstand the info, think the threat is worse than it is” “People might panic if we told them the truth”

US Nuclear Reg. Comm. Guidelines for External Risk Communication (2004) concerning holding back info because prelim. conclusions may be contradicted by further analysis: “Communicate early and often…failure [to do so] breeds mistrust and gives others the opportunity to frame the issues.”

Immediate, Urgent Issues (as of Christmas 2004)

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 (radar saved us).

Does NASA (or asteroid community) 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:

Info as of mid-January 2005:Info as of mid-January 2005:

* Diameter about 320 m * Composition: ordinary chondrite? * Misses by 5 Earth diams. in 2029 * 5th mag. from Europe on 13 Apr. 2029

Then Things Changed Again! 3 Feb. 2005: Arecibo radar

discovers that MN4 will pass twice as close to Earth in 2029! Under the height of

geosynchronous satellites! It will sail across European

skies as a bright star (42 deg/hr, 3rd magnitude)!

1-in-1300-year event! (JPL press release, but…???)

MN4 could pass thru a key-hole that would result in Earth impact later in the 2030’s

Gravitational tides could physically alter the asteroid (shape, spin, interior)

Future Observability of Apophis

As an Aten, Apophis is often faint, near the Sun

Radar opportunities occur every 8 years

There is not steady improvement in knowledge of its orbit and impact chances

Optical

Radar

Steve Chesley (2006)

We think of apparitions We think of apparitions occurring every 1 to 2 occurring every 1 to 2 years…years…not truenot true for many for many NEAS!NEAS!

Evolution of Uncertainty

Chesley’s analysis of how uncertainty in km on 2029 b-plane evolves: shows major jumps in 2013 and 2021.

Radar is vital for reduced keyhole-scale uncertainties in final decade.

Several-% chance we will need a transponder mission in the 2010’s

Impact on Apr. 13th, 2036?

Chances currently [4/20/06] rated 1-in-6200 (JPL and NEODyS)

Must pass through keyhole 600 meters wide

The B612 “gravity tractor” scheme could move it away from keyhole, if we get started soon enough Radar possibility (May 6-8) could refine

orbit so that 2036 threat vanishes, but… 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

Delta-v to Deflect Changes from Year to Year

It is easier to push earlier, but there are important “jumps” in the required delta-v

This diagram was relevant to a 2029 impact

An extreme example pertains to 2036 impact: you only have to push to avoid the keyhole, not to move it by an Earth’s radius

Carusi (2005)

Gravity Tractor to the Rescue!

From Lu & Love, Nature, 2005

Scientist/ astronaut Ed Lu

Artwork by Dan Durda

Path of Risk for Apophis favors tsunami, west Coast US, north coast S. America. Modest push before 2029 could avoid 600m keyhole. Gravity tractor is control-lable, needs not interact with surface of Apophis (with its unknown properties).

Stan Ward (preliminary)

Points where Standard Errors should be Enhanced by Meta-Errors

Astrometry from original KPNO, later Siding Springs, and revisited Spacewatch observations had poor or non-existent stats (different weighting judgments at JPL, NEODyS) Led to ad hoc analysis after recovery, badly wrong all-clear

prediction (it was all-clear, but distance grossly in error) Estimates of size and mass of Apophis

Initial estimate based on H alone; no initial consideration of range of possible sizes due to bimodal distribution of albedos (had it been a C-type, ~20% chance, it might have been a >1 km potential civilization killer, TS=7)

Binzel’s size estimate is very indirect (inference from spectrum he interprets as Q-type, but where is 2-micron band?)

What observational biases apply? If we know “size”, we still don’t know mass, or whether it is a

binary How do we weigh errors in optical vs radar measurements?

What are appropriate errors in the widths of “Paths of Risk”? What are the true cross-track uncertainties? What errors are introduced by approximations used in

calculations?

Wavelength (microns)

Some Lessons Learned… or at least some issues to be discussed!

These impact possibilities and near-misses almost always have unexpected attributes (a rocket not an NEA, “came from the Sun,” discovered by uncharacterized telescope, discovered on a weekend or holiday, poorly understood data imply it will hit “tomorrow,”…). We must continue to expect the unexpected.

We must quickly and rigorously search for pre-discovery observations: the public considers it a mistake if we announce a possible impact when we already have data disproving it.

We must use meta-error bars, that take into account not only formal errors, but biases, approximations, Bayesian statistics, etc.

We must continue to re-evaluate and pre-plan our public communications, bring them in line with professional risk-communication guidelines. (For example, Apophis teaches us that the T.S. wording “new telescopic observations very likely will lead to re-assignment to TS=0” can be wrong: for several days, the new observa-tions led to higher TS ratings…could have avoided TS=0 for months.)

We must act as though the impact will happen, even as we say that the chances are small (unless the threat is truly negligible).

Some Lessons Learned … (2)

Procedures for updating of JPL & NEODyS predictions, and choices about weighting, need to be revisited to reduce confusion (Apophis impact probability for 2036 differed, unnecessarily, by a factor of 2 a month ago).

We’re reminded once again that we must institutionalize the impact hazard into the structures of national and international disaster management agencies…we must further standardize our own procedures, and we must know how and when to report up the chain-of-command and to the public, if the threat warrants it. (In the US, astronomers report to Lindley Johnson, but when does NASA report to FEMA? Who do non-U.S. astronomers report to?)

We are still learning the behavior of resonant return impact threats. Nature will hold further surprises for us. Robust scientific research about NEAs must keep up with the rapidly increasing discovery rate expected over the next few years.

Even an impact threat decades away may require near-term actions.