Subject: Sound bites on asteroid searches
From: David Morrison
Submitted: Wed, 26 Feb 2003 09:33:55 -0800
Message number: 80
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Colleagues:
This is a follow-up to my note yesterday about the non-statistical
nature of an asteroid search carried out for the purposes of
planetary defense. You may be interested in the following "sound
bite" statements that I have found can help to make these and related
points. (Reactions are welcome, especially if you don't agree with
any of these statements.)
David Morrison
==================================
In the real world, impacts are deterministic: There either is or is
not an asteroid that will collide with Earth during this century.
Asteroids do not change orbits capriciously except in Hollywood.
We already know the statistics and the risks -- what we need now is
to search for individual objects, one at a time. The public
requirement is to find the next impactor before the Earth collides
with it.
Many science objectives can be met with statistical samples, but
planetary defense requires a complete survey.
The public does not care if the annual risk of dying from an impact
is one in a million or one in two million -- they want to know if it
will happen to them.
When you cross a busy intersection, you don't ask what the statistics
are on pedestrian accidents -- you look to see if a car or truck is
headed toward you.
There is no last-minute warning system: Either we discover an
asteroid and predict its impact decades or centuries in advance, or
else it strikes without warning -- the first you will know is when
the sky lights up and the ground starts to shake.
The individual risk is dominated by objects large enough to produce a
global environmental disaster -- one that places you at risk anywhere
on the planet.
The most likely impact is a small one, but the most likely impact to
endanger you (or any individual) is a big one.
A large country (like Russia, China, USA) is more likely to be hit,
but its citizens are no more at risk than those of a small country.
We have a choice: Deal with the small impacts that hit more
frequently but pose very low risk, or deal with the large ones that
are infrequent but are more likely to kill you. (The current
Spaceguard Survey deals with the large ones that pose the greatest
risk)
You have more to fear from the residual 10% of big ones that
Spaceguard will not have found by 2008 than from the sum of all the
smaller asteroids.
Small cometary impacts (<1 km) are a negligible hazard for the simple
reason that there are few if any such small comets.
The probability of being killed by an asteroid is very low, but it is
larger than the chances of being killed by many other things (e.g.,
defective food or drugs, or leakage from nuclear power plants) that
governments take very seriously.
Impacts are the extreme example of a hazard of very low probability
but very great consequences.
Impacts are the only known natural hazard that could destroy civilization.
Asteroid impacts are the only known natural hazard that can be
eliminated entirely by appropriate application of technology.
--
+++++++++++++++++++++++++++++++++++++++++++
David Morrison, NASA Ames Research Center 240-1
Tel 650 604 5094; Fax 650 604 4251
david.morrison@arc.nasa.gov or dmorrison@arc.nasa.gov
website: http://astrobiology.arc.nasa.gov
website: http://nai.arc.nasa.gov
website: http://impact.arc.nasa.gov
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