[FPSPACE] Looking for a vision

[Jens Kieffer-Olsen]

-----Original Message-----
From: E.P. Grondine [mailto:epgrondine at hotmail.com] 
Sent: Saturday, March 21, 2009 9:37 PM

> When I started reporting on the NEO hazard, both
> George Brown Jr. and Eugene Shoemaker were still
> alive. I never thought that some 12 years later
> senior NASA management would still be doing its
> best to avoid dealing with this hazard.

 That's because NASA should only be concerned with 
 detecting NEOs and not at this stage be directed
 to consider deflecting anything. When given such
 a dual direction, critics of NASA are in effect
 given carte blanche to argue that not enough funds
 go to deflection preparedness.

 Once NASA enters the detection business in earnest,
 some asteroid or comet fragment will soon be
 identified to be on a collision course with Earth.
 Most likely a Tunguska-sized asteroid, and several
 centuries hence. It's unlikely that any action
 needs to be taken though, since over time it will
 become apparent approximately where the impact is
 due to take place. 

 In the improbable case that a behemoth object is
 found heading our way - maybe a comet fragment -
 then the matter should move from NASA up to the
 White House. It's not to be expected of NASA that
 they roll a ready-made deflection plan out their
 corporate sleeve.

 And yes, other national or supranational agencies
 should work along the same lines.

> As you are undoubtedly aware, for its own internal
> reasons NASA has been relying on Morrison's estimate
> that asteroids are 95% of the threat, while comets
> are only 5%. I believe you and I both are fairly
> certain that these numbers are wrong, and that the
> ELEs are due to cometary impact, and have been
> occurring at a roughly regular rate of 1 per
> 26 million years. In other words, Clube and Napier
> were right on the injection mechanism and Morrison
> and Muller wrong. 
>
> What that works out to hourly I don't know.

 It's a three-dimensional problem, isn't it? You
 focus on the comet versus asteroid ( ie. orbit
 type ) dimension, which is indeed important. But
 it's equally important where on the scale from
 50m to 20km the object belongs. And whether the
 impact is due this decade, century, millennium,
 or later, ie. the time dimension.

 I agree with you that comets are unlikely to make
 up only 5% of the ELE threat. Do you suggest 50%
 or more?

 On the other hand I find it hard to disagree with
 an estimate of 95% of Tunguska-sized impacts to
 stem from asteroids.

 As for the validity of my rule of thumb, it
 obviously depends on how exactly we define an ELE.
 Let's call an impact from a one-mile-wide object
 an ELE, even if 5-10% of mankind survives :-) 

 Assuming one 75m ( Tunguska-like ) impact per
 100 years and applying a 2.3 power rule ( from
 memory what Frank Crary once wrote ) we find
 that a 1600m object hits every (1600/75)**2.3
 x 100 years ~= 114,000 years.

 As there are 24x365 ~= 8,760 hours in a year
 the risk of an Extinction Level Event is then
 one in a billion PER HOUR.

--
Jens Kieffer-Olsen
Slagelse, Denmark