Clark R' Chapman

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2008 TC3 Short Term Warnings Dominate NEO
Hazard Mitigation and General Perspectives on the
Hazard

• Clark R. Chapman
• Southwest Research Inst. B612 Foundation

Steven J. Ostro Memorial Symposium on Planetary
Radar and Near-Earth Objects Jet Propulsion
Laboratory, Pasadena CA 4 June 2009
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The NEO Impact Hazard

• As originally articulated in the early 1980s,
  the hazard involved mass extinctions, or at least
  the destruction of human civilization.
• From the early 1990s, when the Spaceguard Survey
  was proposed, through its implementation in 1998,
  the goal was to catalog NEAs gt1 km in diameter
• and to calculate whether one might hit decades
  in the future.

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Making Asteroids Real

• But it was all pretty fantastical and
  abstractthe odds of Armageddon were so tiny, the
  destruction of everything in an instant so
  difficult to imagine
• Steve Ostro was an early proponent of making Near
  Earth Asteroids and the hazard they pose and
  their potential role in exploring the solar
  system concrete, visualizable, and real.

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Making Asteroids Real
these objects were unknown until recently, are
invisible to the naked eye, and are boring dots
through even big telescopes. Unlike Mars, they
haven't been part of human consciousness since
the dawn of intelligence. I hope that
publication of the radar results on Toutatis and
Geographosand release of animations of these
objects (and Castalia) and orbits around them
will help to make NEAs more real. Steve
Ostro to L. Friedman, 4 April 1995.
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So the Fantastic was Made Real
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Visualizing the NEA Swarm

• It was not just the shapes and configurations of
  NEAs revealed by radar that Steve wanted to
  share
• NEAs dominate the Earths interplanetary
  environment

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Another worthwhile project would exploit
state-of-the-art planetarium technology to make
the largest 10,000 NEAs and their motions
visible on the celestial sphere. If such
visibility had been built into nature, who knows?
Maybe NEAs would have been populated long
ago. Steve Ostro, April 1995
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If we could only see in the infrared (like WISE
will do)

• STEVE OSTRO Imagine, for a moment, if
  instead of these objects being tiny and not
  visible to the naked eye, they were suddenly made
  visible. Suppose that there was a button you
  could push and you could light up all the
  earth-crossing asteroids larger than about ten
  meters. There would be over a hundred million of
  these objects in the sky, and you'd go outside at
  night, and instead of being able to see a few
  thousand bright stars, the sky would be filled
  with millions of these objects, all of which are
  capable of colliding with the earth. 
•  
• PBS, Nova, The Doomsday Asteroid,
  31 October 1995

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What is the Reality of the NEO Hazard?

• for the public, public officials, and
  politicians?
• What scenario will agencies (DoD, FEMA, NASA)
  most likely face?
• What situation will we most likely have to
  address, as asteroid experts, in our lifetimes?

It is NOT worrying about blowing up a huge
asteroid with a bomb, nor deflecting an Apophis
away from the Earth. It is finding and tracking
a mini-Tunguska during the last weeks and days
before impact, and evacuating people from ground
zero. Steve Ostro participated in developing
that understanding, and Goldstone and Arecibo
will likely play an essential role in effecting a
successful evacuation, if this scenario comes to
pass.
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Understand the Power-LawSmall Ones Happen Much
More Often

• We think about the big ones, which might threaten
  civilizationand we should.
• But the most likely kind of event that
  politicians, officials, and the public will have
  to deal with are the smallest predicted impacts
  that might be dangerous (Spacelabs re-entry in
  1979 was an extreme example).
• Lately we have been thinking of Apophis as
  typical of an NEA impact threat it is not!
• For every Apophis, there are more than 50
  Tunguskas, and 1000 impacts by 15 m NEOs that
  might compel officials to act.

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What is the Smallest NEO that is Dangerous?
Model of 30 m NEA 1998 KY26 (radar)
This will be a vital issue for decision-makers

• Metallic objects are little impeded by the
  atmosphere, whatever their size they form most
  craters lt1 km diam. but are only 3 of
  NEOs.
• Carancas-like anomalous stones are probably rare.
• The 2003 SDT report considered 50 m diameter to
  be the smallest truly dangerous
  non-metallic NEO.
• Bosloughs recent study of Tunguska suggests that
  the threshold for danger may be nearer 30 m
  diameter.
• Should we then be unconcerned about deflection/
  evacuation for a 25 m body? They impact 10
  times as often as 50 m impactors.
• A nominal 25 m body may actually be 50 m in
  diameter (because of bimodal albedo
  distribution).
• What will public officials do about a predicted
  impact by a 15 m NEO? Be prudent evacuate!
  (They impact 30 x as often as 50 m impactors,
  20 chance this decade.)

? LSST 15 m NEO?
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Virtual Impactor Search Short Term Warning!
Palmer Divide Observatory

• At any time, there are numerous low-probability
  impacts listed on the JPL Sentry Risk website.
• In some cases, the NEA may not be observable
  again until its possible final plunge.
• Milani et al. developed the concept of virtual
  impactors, those NEOs from within the whole
  cloud of uncertainty that will impact by
  tracking the orbits of v.i.s, observers can look
  and see if the real NEO is following the
  trajectory of a v.i.
• The approach is to search telescopically for the
  virtual impactors that would strike the Earth
  during the weeks prior to impact.
• If the NEA is found on a v.i. course, then warn!
• If no NEA is found, then we are safe.
• If the NEA is coming from the direction of the
  Sun, radar would be needed to search for v.i.s.

Arecibo
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Radar is Vital for Short-Term Warnings

• In an extensive email discussion between Ostro,
  Schweickart, Morrison, Harris, and Chapman 2-4
  Jan. 2008, the rationale was developed.
• It all began with Mars Asteroid 2007 WD5,
  discovered in late December 2007, had an
  unusually high chance of striking Mars on 30
  January 2008. Would any erstwhile Martians see
  it coming? It was coming from the direction of
  the Sun, so they would need radar. But would it
  work? Would radar work in an analogous case for
  Earth?
• Steve Ostro calculated that it would work!

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A New Rationale for Arecibo
in essence, we've now realized/articu-lated a
new and unique rationale for the Arecibo radar.
Not search not backing up or refining the
optical tracking but actually providing
critical information for the emergency planning
and management folks who will ultimately be
responding to poten-tial NEO threats. The
overwhelming information will be all clear not
this time but the potential is always there that
it may turn out the other way round and that
Yikes! This time, and here's the specifics.
Rusty Schweickart to Steve Ostro, 1/04/08
As far as a demo, my colleagues and I generally
try to identify any NEA radar opportunity. We are
less energetic with several-decameter (H 25)
objects, because they are not PHAs, telescope
time is very tight, and we have no hope of making
nice delay-Dop-pler images. However, if an object
is on the risk page with poor prospects for
optical removal, and there is a good opportunity
for radar detection, it would definitely deserve
very high priority. Steve Ostro to
Schweickart and Chapman, 1/04/08
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First Recognition of a Short-Term-Warning Policy
Issue
We have repeatedly, from the beginning, asserted
that Spaceguard will find threatening NEAs
decades or centures before they hit. Thus, until
recently, there has been very little discussion
of reacting on a warning time-scale of weeks,
months, or even years. Yet here we are talking
about less than two months of warning and
thinking about "what if Earth were the target".
This seems inconsistent with our assumptions and
assertions that if we find a NEA on a collision
course, we will have many years of warning. I
think that policy makers (or their staffs) will
see this same contradiction and ask us to
re-evaluate the issue of short warning times. --
D. Morrison (to Harris, Schweickart, Ostro, and
Chapman) 1/03/08.
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2008 TC3 Some Background

• NEA discovered 7 Oct. 2008, predicted to impact
  Sudan 20 hours later.
• Before impact, other telescopes observed TC3s
  physical properties.
• Nearly 300 pieces of rare ureilite meteorites
  recovered.
• TC3 was 4 meters diameter, roughly an annual
  impact on Earth.
• Spaceguard Survey was expected to find only
  1-in-1 million TC3-sized NEOs.
• Was it a miracle that we found beforehand what
  was plausibly the largest NEA to impact Earth in
  2008?
• NO! Astronomers overlooked Spaceguards
  short-term warning capability.

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Short-Term Warning Capabilities of NEO Surveys

• Current Spaceguard Survey will find 35 of NEAs
  gt30 m diameter on final plunge could be
  improved to 50 or better.
• It is 100 times more likely that the Spaceguard
  Survey will find a gt30 m impactor on its final
  plunge than that it will find one long in advance
  that will eventually hit.
• Next generation survey (LSST, Pan-STARRS)
• could find 35 of impactors gt2 m diameter
• May require difficult-to-change observing cadence
• Requires different data-reduction and reporting
  protocols
• for gt30 m NEAs, there are similar chances for
• Short-term warning
• Long-term warning
• No warning at all
• Short-term warning was not studied for the
  current Spaceguard Survey SDT (2003) did study
  short-term warning for next generation surveys.

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Short-Term Warning None of us Got it Right
Consider a 3040-m office-building-sized object
striking at 100 times the speed of a jetliner.
Even with the proposed augmented Spaceguard
Survey, it is unlikely that such a small object
would be discovered in advance impact would
occur without warning. C. Chapman, EPSL (2004).
A commonly asked question is how much warning
time we'd need to mitigate a collision with, say,
a 100-m asteroid. (Larger objects would require
at least as much warning, so the 100-m case
serves as a lower limit.) I think a few years
would be impossible, whereas 50 years should be a
piece of cake. -- Steve Ostro to Rusty
Schweickart, 29 Dec. 2001
a short lead time for an NEO is extremely
unlikely we can expect either decades of
warning or none at all Morrison, Harris,
Sommer, Chapman Carusi (Asteroids III 2002)
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Public Officials Must Make Decisions Much More
Often than NEOs will Hit
Low Probability Impact What is the Threshold
for Action? 20? 5?

• Post-disaster rescue and recovery if NEO strikes
  undetected.
• Warnings for evacuation, disaster-preparedness if
  there is a short-term warning.
• Preparing for a low-probability chance that a
  virtual impactor proves to be about to strike.
• Preparing for Apophis-like scenarios decisions
  to launch a pre-deflection mission (e.g.
  transponder with Gravity Tractor capability) must
  be made long before keyhole passage, perhaps very
  long before the threatened impact.
• Evaluation of marginal impact scenarios
• Predicted impact by NEO 15 m diameter just
  watch the fireworks or be prudent?
• Immature or spurious impact warnings

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Relative Frequency of NEO Event-Types and
Required Actions

• Hyped or unreliable media news stories.
  Officials irritated but must do nothing. Annual
  ? more often?
• Impact predictions for future decades requiring
  analysis, but leading to no action. 20/decade ?
  several per year.
• Short-term impact warning for 15 m NEA.
  Immediate evacuation would be prudent.
  7/decade ? 15/decade.
• Prediction of an impact during next 50 years
  eventually requiring launching of a transponder
  mission (for NEAs gt 100 m). 1 chance ? 15
  chance.
• Short-term impact warning for gt40 m NEA.
  Immediate evacuation required (by ships or from
  ground-zero). 0.3/decade ? 1/decade.
• Detection of NEA gt100 m that would ultimately
  impact during next 50 years if deflection isnt
  attempted or successful. 0.01 ? 0.2.
• Detection of civilization-threatening NEO that
  will strike in next 50 years. 0.001 ? 0.0003
  chance.

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What is the Primary Mitigation Approach
Evacuation or Deflection?
Both!

• Evacuation
• Why it is Important
• By far the most likely case we will face
• Attributes
• Inexpensive and familiar apply usual all
  hazards emergency procedures
• Requires rapid, reliable communications between
  astronomers and officials, and famililarity with
  the issues by emergency managers.

• Deflection
• Why it is Important
• Only responsible way to prevent global or
  regional-scale disaster from happening.
• Attributes
• Deflection implementation is much less likely
  than the need to evacuate.
• Advance decisions must be made when need to
  deflect is still not known.
• Expensive! Especially if need uncertain.

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2009 KK Another Apophis?

• 270 m diameter.
• 137 keyhole passage in two weeks?
• 1 thousand MT impact on 29 May 2022 now
  1-in-10,000 chance. Torino Scale 1.
• If Arecibo cant get it by 15 June, the next
  radar opportunity wont happen until autumn of
  2020.
• Visible optically from now until Jan. 2010, then
  poorly visible or invisible until 2020.
• Is it too big, too late, to deflect? Evacuation
  may be the only option.

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NEAs in our Future
I think two things have to happen during the
next few decades to connect our time to the
long-term future of civilization in a manner that
positively takes responsibility for our
destiny a successful B612 experiment and a human
mission to a near-Earth asteroid. -- Steve
Ostro, 31 Jan. 2003
Unless we were implausibly lucky in having
Castalia, Toutatis, and Geographos be the first
NEAs to be reasonably well characterized from
spatially resolved images, most of them are
unbelievably strange. Close orbits (and
certainly any landing orbits) around very
irregularly shaped bodies are geometrically
complicated, highly counter-intuitive, strikingly
beautiful I hope I live to see humans in such
orbits. Steve Ostro, 4 April 1995.
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