Napier: Not So Fast Bos... Bill Napier answers Mark Boslough dismissal of comet fragment swarm impact events, CosmicTusk blog: Rich Murray 2013.02.15

[Rich Murray-2]

Napier: Not So Fast Bos... Bill Napier answers Mark Boslough dismissal
of comet fragment swarm impact events, CosmicTusk blog: Rich Murray
2013.02.15
http://rmforall.blogspot.com/2013/02/napier-not-so-fast-bos.html


Napier: Not So Fast Bos….
[ George A. Howard starts... ]

Bill, will you help the Tusk out a bit and provide a response, which I
can post, to the claim below by Dr. Mark Boslough?
There are several ways to approach his statement, but I am interested
in your take.

“There’s no plausible mechanism to get airbursts over an entire
continent,” said Boslough.

Sent from my iPhone, George A. Howard

Response from Bill Napier that day:

You asked me to comment on Mark Boslough’s claim that “There’s no
plausible mechanism to get airbursts over an entire continent.”
As I’ve already demonstrated in the refereed literature that there is
such a mechanism, I’m not sure what I can add!
However, let me try to pinpoint where I believe Boslough is going wrong.
I have in hand an abstract of a talk he gave a couple of years ago and
I don’t suppose his stance has changed much since then:

“The YDB impact hypothesis of Firestone et al. (2007) is so extremely
improbable it can be considered statistically impossible in addition
to being physically impossible.
Comets make up only about 1% of the population of Earth-crossing objects.
Broken comets are a vanishingly small fraction, and only exist as
Earth-sized clusters for a very short period of time.”

~The Bos, Geol. Soc. America annual meeting (21-23 Nov 2010), Denver.

It’s true that comets currently make up a minority of the population
of Earth-crossing objects (1% is extreme but let that pass), but
that’s only at the 1 km level or thereabouts.
As you go to larger objects, the balance shifts profoundly.
For example, there are no 10 km asteroids currently in Earth crossing
orbits, but we do have large cometary Earth-crossers, e.g., Halley at
11 km, Swift-Tuttle at 27 km and so on.
Asteroids of 10 km or more can’t be shifted out of the main belt at a
sufficient rate to account for the large terrestrial impact craters:
the transfer rate is an order of magnitude too slow.
The action lies with the big comets.

Large populations of them have been discovered on the fringes of the
planetary system in recent years, thanks to deep, wide-angle surveys.
Their number is still uncertain, and their orbital dynamics is still
being worked out, but it is recognized that from time to time rare,
giant comets will feed into short-period orbits from these
populations, weaving between the giant planets in unstable orbits
which may lead to their entering our neighbourhood on relatively short
timescales.
They do this for the most part by feeding through the Jupiter family
of comets, that is short-period comets whose orbits are strongly
influenced by that giant planet.

Chiron, for example, which is over 200 km in diameter and orbiting
beyond Saturn, has probably dipped in and out of our neighbourhood
several times in its past.
The half-life for doing so is about 0.2 million years, each episode
lasting a few thousand years.
It probably has several thousand times the mass of the entire
near-Earth asteroid system.
There are several known bodies in this size range and similarly
unstable orbits, and the sample is likely incomplete.
Large-scale orbital computations have shown that they have the
propensity to become Earth-crossers on timescales (each) of order a
million years.

It follows from this that a giant comet residing in a short-period,
Earth-crossing orbit is not uncommon on geological timescales.
There is nothing anomalous about an erstwhile giant comet having been
around say over the last 100,000 years.

This is all by way of background because we know that in fact two such
comets have indeed been around in the recent past.
One is the progenitor of the Kreutz sungrazers, which was probably 100
km across and began to break up 1700 years ago.
The other is the progenitor of comet Encke and the Taurids, which was
probably of similar size but much greater age, at least 20,000 and
perhaps up to 100,000 years.
Kreutz was high inclination and its debris never came our way.
Encke is in the ecliptic and we’re still immersed in the debris, the
Taurid complex.

Which leads to the question: what do we expect from a 100-200 km comet
in a short-period Earth-crossing ecliptic orbit?

“Broken comets are a vanishingly small fraction, and only exist as
Earth-sized clusters for a very short period of time.”

~The Bos

This one sentence contains two profound misconceptions.
First, hierarchic disintegration is now generally recognised as the
major route whereby comets die.
It’s a common process.
Second, ‘Earth-sized clusters’ have nothing to do with it.
We are dealing with concentrations of fragments having, say, 10,000
times the cross-sectional area of the Earth.
For a 100 km comet to undergo disintegration in our neighbourhood
gives us a hugely enhanced impact hazard.
Fragments totaling even a 1,000th the size of Chiron would have a mass
of 10**18 g.
Passage through such a debris field would yield about 10** 14 g of
material impinging on the Earth.
This is likely to be in the form of dust, pebbles, all the way up to
super-Tunguska objects.
The overall energy amounts to something like 5000 Tunguskas, striking
a hemisphere of the Earth over a period of a few hours as we pass
through.
What are the odds that we would in fact pass through such debris in
the course of a short-period, giant comet’s disintegration?
This communication is already quite long enough, but detailed
numerical modelling based on lifetimes, drift, shepherding resonances
and the like reveal that one or two such encounters are reasonably
probable events over the active lifetime of the Taurid progenitor
(papers in preparation; see also my 2010 MNRAS paper).

In a nutshell, Mark Boslough’s cometary model is irrelevant.
It has nothing to do with the actual circumstances which prevailed in
our environment over the Holocene and earlier.
It takes no account of, and indeed shows no awareness of, modern
developments in cometary dynamics.
Any competent referee would reject it.

I could say more, but perhaps that’s enough to be going on with.

Best regards,  Bill

February 13th, 2013 | Tags: clovis, comet, LeCompte, mark boslough,
pinter, pranks, sandia, surovell, younger dryas | Category: bill
napier, Guest blogs, impact frequency, Mark Boslough, New Papers


Rise of the Zombie: Harvard Discovers Evidence for Major Earth Impact
at Younger Dryas Boundary
[ George A. Howard comment ]

“The theory has reached zombie status,” said Professor Andrew Scott
from the Department of Earth Sciences at Royal Holloway. “Whenever we
are able to show flaws and think it is dead, it reappears with new,
equally unsatisfactory, arguments. -- January 30, 2013, Royal Holloway
Press Release two weeks before the Harvard discovery

Concluding remark: The main conclusion of our study is the detection
of an unusual event during the Bølling-Allerød-YD transition period
that resulted in deposition of a large amount of Pt to the Greenland
ice.The nature of the event remains uncertain, but our results clearly
rule out an impact or air burst of a chondritic bolide. If an impact
was involved, the impactor had a very unusual composition deriving
from a highly fractionated portion of a proto-planetary core.

-- Petaev, Huang, 2013

[ free full text available via Scribd ]


George Howard at cosmictusk.com blog cites reliance on Todd Surovell
2009 paper by Mark Boslough 2012 Dec. critique of 2007 Richard
Firestone YD comet fragment impact storm hypothesis -- Malcome
LeCompte 2012 Sept. backs up Firestone: Rich Murray 2013.02.10
http://rmforall.blogspot.com/2013/02/george-howard-at-cosmictuskcom-blog.html


Aug 31 to [hidden email]

smooth blue-black melt glaze on 2 sharp red-brown nearby surface rocks
under left side of Mount Sharp in Curiosity Mars panorama? Rich Murray
2012.08.31

http://www.panoramas.dk/mars/curiosity-first-color-360.html

high resolution adjustable view --

compare with surface glazes on sharp rocks in California and New Mexico:

pertinent features near Campbell Mountain, studied by Dennis Cox, by
his house in Fresno, CA: Rich Murray 2011.06.27
http://rmforall.blogspot.com/2011_06_01_archive.htm
Monday, June 27, 2011
http://tech.groups.yahoo.com/group/astrodeep/message/87

It is easy in a few hours to locate pertinent features to the N, E,
SE, and S of Campbell Mountain, studied by Dennis Cox, a few miles NE
of his house in Fresno, CA.

Maybe some of us can visit for a weekend and drive around, as many
intriguing sites can be found by roads.

http://craterhunter.wordpress.com/the-planetary-scaring-of-the-younger-dryas-impact-event/california-melt/

https://skydrive.live.com/?cid=5d6b9f6c30c6fe9f&sc=photos&id=5D6B9F6C30C6FE9F%21\1348
19 images of Fresno mountains and rock samples

Dennis Cox blog, plain text, with images of samples of magnetic black glaze
on melt rocks from 13 Ka ice comet fragment extreme plasma storm geoablation
in Fresno, California: Rich Murray 2010.07.02
http://rmforall.blogspot.com/2010_07_01_archive.htm
Friday, July 2, 2010
http://tech.groups.yahoo.com/group/astrodeep/message/53

photo of typical air burst geoablation glaze on hard bedrock at top of
Mount Helix park, E San Diego: Rich Murray 2012.03.15
http://rmforall.blogspot.com/2012/03/redbrown-glaze-on-hard-crystalline.html
http://rmforall.blogspot.com/2012/03/photo-of-typical-air-burst-geoablation.html
http://tech.groups.yahoo.com/group/astrodeep/message/98

10 m broken rock hill with black glazes, W of Rancho Alegre Road, S of
Coyote Trail, W of Hwy 14, S of Santa Fe, New Mexico, tour of 50
photos 1 MB size each via DropBox: Rich Murray 2011.07.28 2011.08.03
http://rmforall.blogspot.com/2011/08/10-m-broken-rock-hill-with-black-glazes.html
http://rmforall.blogspot.com/2011/08/35479730-106085926-1865-km-el-top-10-m.html
photos 3-5 of 50
http://tech.groups.yahoo.com/group/astrodeep/message/92

within the community of service,

Rich Murray,
Imperial Beach, CA 91932
[hidden email]
 505-819-7388  cell
 619-623-3468  home
http://rmforall.blogspot.com

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