[FPSPACE] Canada takes lead from NASA

[Jens Kieffer-Olsen]

-----Original Message-----
From: E.P. Grondine [mailto:epgrondine at hotmail.com] 
Sent: Wednesday, May 20, 2009 6:54 AM

 [snip]

> But the problem is that COMETS and COMET PIECES and not
> asteroids form the bulk of the impact hazard. Read my
> book for details.

 G'day, Ed

 Let's research what a qualified reader thinks of your
 book "Man and Impact in the Americas". A year ago
 almost to the day Eric Stevens wrote, cf.
 
http://sci.tech-archive.net/pdf/Archive/sci.archaeology/2008-05/msg00519.pdf

 [...] the cited evidence for some of these events is
 so tenuous that in a number of places the reader has to
 deduce their occurrence from the migrations, invasions
 and cultural changes described in the text. I am a
 long-time convert to the general concept of coherent
 catastrophism as originally espoused by Clube and Napier
 but even I would like to see some evidence for specific
 impacts. [...] I found the book a fascinating, if possibly
 slightly eccentric, potted history of the pre-European
 peoples of the Americas. I am glad that I have read it
 once but I found it such heavy going that I am unlikely
 to read it a second time."

 Not bad at all for a book published more than a decade ago!

 However, research has moved on since. One of to-day's
 foremost experts is Bill Bottke. In 2007 he wrote, cf.
 
http://www.boulder.swri.edu/~bottke/Reprints/Bottke_ICSU_2007_Asteroids-Chap
ter-09.pdf

 "If we assume the bulk densities for a cometary nucleus
 and an S-type NEA are 0.6 and 2.6 g cm-3, respectively,
 and the mean Earth impact velocities for long-period
 comets and NEAs are 55 and 23 kms-1, respectively, then
 the average impact energy of a long-period comet impact
 would be only 30% more than a similarly-sized NEA that
 impacts the Earth. Stokes et al. (2003), using these
 results as well as methods described in Sekanina and
 Yeomans (1984) and Marsden (1992), showed that the
 threat of long-period comets is only about 1% the
 threat from NEAs. Thus, asteroids rather than comets
 provide most of the presentday impact hazard."

 That of course does NOT imply we should ignore the threat
 from hazardous comets. In fact, since they are so much
 harder than asteroids to both detect and deflect, the
 effort to map their orbits deserve thick wads of cash,
 both USD, Canadian, and for that matter HKD.
 
--
Jens Kieffer-Olsen
Slagelse, Denmark