[meteorite-list] Mark Boslough poster and video re Libyan Desert Glass -- simulation of geoablation from meteor air burst 29.5 Ma: Rich Murray 2011.02.27

From: Rich Murray <rmforall_at_meteoritecentral.com>
Date: Sun, 27 Feb 2011 01:15:38 -0700
Message-ID: <AANLkTik-sFRjaXX_nKz-iobY1qz7_eNKL=Ohfzc1K88f_at_mail.gmail.com>

Mark Boslough poster and video re Libyan Desert Glass -- simulation of
geoablation from meteor air burst 29.5 Ma: Rich Murray 2011.02.27
http://rmforall.blogspot.com/2011_02_01_archive.htm
Sunday, February 27, 2011
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http://groups.yahoo.com/group/astrodeep/message/81
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____________________________________________________________


[ Thanks to Dennis Cox http://craterhunter.wordpress.com/ ]

http://dl.dropbox.com/u/2268163/DesertGlass.pdf

2 page

Computers and Information Sciences
Red Storm [ supercomputer, Sandia Labs, Albuquerque, New Mexico ]

High performance computing provides clues to scientific mystery
Enigmatic silica glass in the Sahara desert has survived nearly 30
million years.
How did it form?

(Left) Libyan Desert Glass is found in an area spanning 6500 km2, in
the Great Sand Sea of the Western Desert of Egypt, near the border
with Libya.
In 1998, an Italian mineralogist showed that a carved scarab in King
Tut?s breastplate was made out of this glass.
Red Storm was used to simulate the airburst and impact of a 120-meter
diameter stony asteroid.


      Most natural glasses are volcanic in origin and have chemical
compositions consistent with equilibrium fractional melting.
The rare exceptions are tektites formed by shock melting associated
with the hypervelocity impact of a comet or asteroid.

Libyan Desert Glass does not fall into either category, and has
baffled scientists since its discovery by British explorers in 1932.
The 1994 collision of Comet ShoemakerLevy 9 with Jupiter provided
Sandia with a unique opportunity to model a hypervelocity atmospheric
impact.
Insights gained from those simulations and astronomical observations
of the actual event have led to a deeper understanding of the geologic
process of impacts on Earth and presented a likely scenario for the
formation of Libyan Desert Glass.

 High-resolution hydrocode simulations, requiring huge amounts of
memory and processing power, support the hypothesis that the glass was
formed by radiative heating and ablation of sandstone and alluvium
near ground zero of a 100 Megaton or larger explosion resulting from
the breakup of a comet or asteroid.

      Using Sandia?s Red Storm supercomputer, we ran CTH shock-physics
simulations to show how a 120-meter asteroid entering the atmosphere
at 20 km/s (effective yield of about 110 Megatons) breaks up just
before hitting the ground.
This generates a fireball that remains in contact with the Earth?s
surface at temperatures exceeding the melting temperature of quartz
for more than 20 seconds.
Moreover, the air speed behind the blast wave exceeds several hundred
meters per second during this time.
These conditions are consistent with melting and ablation of the
surface followed by rapid quenching to form the Libyan Desert Glass.
These simulations require the massive parallel processing power
provided with Red Storm.

       The risk to humans from such impacts is small but not negligible.
Because of the low frequency of these events, the probability and
consequences are both difficult to determine.
The most likely scenario that would cause damage and casualties would
not be a craterforming impact, but a large aerial burst
similar to the one that created this unusual natural glass.
This research is forcing risk assessments to recognize and account for
the process of large aerial bursts.

[ supercomputer simulation images in color of vertical impact torch
hitting ground from air burst with very complex curling flows
3.80 sec frame 205 in Part 5 of NG video documentry
4.00 sec frame 210 torch hits ground
5.00 sec
7.49 sec frame 228
9.99 sec frame 232 ~5 km ground radius, gives expansion velocity ~800
m/sec after hitting ground at 4 sec, to 6 sec later at 10 sec. ]

Ablated meteoritic vapor mixes with the atmosphere to form an opaque
fireball with a temperature of thousands of degrees.
The hot vapor cloud expands to a diameter of 10 km within seconds,
remaining in contact with the surface, with velocities of several 100
m/s.
Simulations suggest strong coupling of thermal radiation to the
ground, and efficient ablation of the resulting melt by the
high-velocity shear flow.

NATIONAL GEOGRAPHIC DOCUMENTRY

      In February, 2006, Mark Boslough participated in an expedition
to the site of the Libyan Desert Glass (LDG).
The glass has a fission-track age of about 29.5 Ma.
There is little doubt that the glass is the product of an impact
event, but the precise mechanism for its formation is still a matter
of debate.
This lively discussion was a featured element of the documentary.
      Evidence for a direct impact includes the presence of shocked
quartz grains and meteoritic material within the glass.
However, the vast expanse of the glass and lack of an impact structure
suggests the possibility of radiative/convective heating from an
aerial burst.
      "Ancient Asteroid" will be shown on the National Geographic
Channel on Sept. 21, 2006.
[ http://www.youtube.com/watch?v=uAmzCR_RSpo 5 parts
Christian Koeberl, geologist

Rarouk El-Baz

John Wasson, UCLA

In Part 5, Frames 205-232 show these 5 images, while other views are
at 149-200, 242-257, 312-328 ]

[ 7 images ]
Camp was set up in ?corridor B? in the southern part of the Great Sand
Sea, within the area of LDG concentration.
Corridors consist of quaternary gravel and alluvium and are separated
by linear dunes. The lower photograph is looking southeast.
Geologic setting is shown by inset map.
LDG sits on silica-rich weathered remains of Upper Cretaceous
Nubia-Group sandstones.
The main area of concentration is 20 km across.

Left: 120-meter asteroid explodes over the Egyptian desert in 2006
National Geographic documentary Ancient Asteroid.

Right: Documentary animators used Red Storm simulation to visualize
the effect of an asteroid explosion in the atmosphere above the city
of London.

Sandia National Laboratories

Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States
Department of Energy?s National Nuclear Security Administration under
contract DE-AC04-94AL85000.

For more information:

Technical Contact:
Mark Boslough, Ph.D. 505-845-8851 mbboslo at sandia.gov

Science Matters Contact:
Wendy Cieslak, Ph.D. 505-844-8633 wrciesl at sandia.gov
_______________________________________________


24.673243 24.95889 .564 km el
crater for Libyan Desert Glass
http://www.tektitesource.com/Libyan_Desert_Glass.html


Impact melt formation by low-altitude airburst processes, evidence from
small terrestrial craters and numerical modeling, H E Newsom & MBE Boslough
2008 Mar 2p abstract: Rich Murray 2010.11.17
http://rmforall.blogspot.com/2010_11_01_archive.htm
Wednesday, November 17, 2010
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3 times more downward energy from directed force of meteor airburst in 3D
simulations by Mark B. E. Boslough, Sandia Lab 2007.12.17: Rich Murray
2010.08.30
http://rmforall.blogspot.com/2010_08_01_archive.htm
Monday, August 30, 2010
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[Extract]

http://74.125.155.132/scholar?q=cache:YY6MFUns_CkJ:scholar.google.com/+%22Mark+B\
oslough%22,+impacts&hl=en&as_sdt=10000000000
[ Extracts ]

"Dr. Boslough has also shown that an LAA from a ~100 meter diameter NEO
melted sand into glass across a region about 10 km in diameter during Libyan
Desert Glass impact ~35 million years ago.
During this event the LAA's fireball settled onto parts of Egypt and Libya
for about a minute with temperatures approaching 5,000 K.
Its hypersonic blast wave extended radially for about 100 kilometers."

NEO Survey: An Efficient Search for Near-Earth Objects by an IR Observatory
in a Venus-like Orbit

Submitted to the Primitive Bodies Subcommittee of the Decadal Survey

Harold Reitsema 2, Robert Arentz 1
Ball Aerospace and Technologies Corp.

ABSTRACT

In 2003 NASA commissioned a Science Definition Team 3 (SDT) to study the
threat posed by Near-Earth Objects (NEOs), to recommend solutions for
efficiently detecting NEOs down to a much lower diameter than before, and to
study techniques for mitigating an impending impact.
Subsequently, the United States Congress directed NASA to investigate ways
to implement many of the SDT's results.
At this time Congress also set the goal of compiling a catalogue complete to
90% by 2020 of all NEOs larger than 140 meters in diameter.
This 90%, 140 meter, 2020 set of goals was named in honor of George E.
Brown, and is henceforth called the GEB requirement.
The SDT concluded that: the thermal infrared (~5 to ~11 microns) is the most
efficient spectral regime for an efficient NEO search;
that any IR aperture from about 50 to 100 centimeters is sufficient;
and that locating a NEO-finding observatory in a Venus-like orbit
(approximately a 0.7 AU semimajor axis) is ideal.
The SDT had to make assumptions about future advancements in detector
technology and deep-space compatible processing power, and assumed that
diffraction-limited optical systems with no chromatic aberrations were
doable within the constraints of a flight mission.
Since then, NASA and its industrial partners, of which Ball Aerospace is one
of many, have flown several deep-space missions, two of which are very
relevant here -- the infrared Spitzer Space Telescope (SST), and the
recently launched Kepler mission, as discussed later.
In this paper we present a high reliability, credibly costed, high-heritage
design that meets the GEB requirements for about $600M (USD).
For no additional cost, this design will detect about 85% of all >100 meter
diameter NEOs, about 70% of all >60 meter diameter NEOs, and about 50% of
all >50 meter diameter NEOs.
These smaller NEOs constitute a newly recognized threat regime that cannot
be efficiently detected from the ground.

...Recent work by Dr. Mark Boslough 4 shows that the impact physics of NEOs
in the 30-100 meter range has been misunderstood due to a process he calls a
Low-Altitude Airburst (LAA), which is a newly recognized threat regime that
has been previously underestimated.
In an LAA event the main body of the NEO comes apart at high altitudes (~80
km to ~10 km), but the object's mass and kinetic energy are conserved as a
fast moving, loosely aggregated, collection of particles which entrain a
column of air reaching the ground in what might be termed an "air hammer."
Dr. Boslough's work shows that the "air hammer" from NEOs as small as 30
meters inflicts significant damage, as was seen in the 30-meter-class
Tunguska event.
Dr. Boslough has also shown that an LAA from a ~100 meter diameter NEO
melted sand into glass across a region about 10 km in diameter during Libyan
Desert Glass impact ~35 million years ago.
During this event the LAA's fireball settled onto parts of Egypt and Libya
for about a minute with temperatures approaching 5,000K.
It's hypersonic blast wave extended radially for about 100 kilometers.
Dr. Boslough has also shown that the interaction of the LAA with the ocean's
surface is much different from a large object's strike, and that any ensuing
tsunami is not yet well modeled.
Therefore any survey instrument capable of searching well below 140 meters
is quite valuable.
Derating the estimate of the Tunguska object's size from ~60 meters to
today's ~30 meters greatly decreases the impact interval
from ~1,000 years to ~200 years.
Given that Tunguska happened 101 years ago, the expected time until the next
impact is ~100 years....

4. Boslough, Mark.
The nature of Airbursts and Their Contribution to the Impact Threat.
Proceedings of the First Annual Planetary Defense Conference,
April 27-30, 2009, Granada, Spain.
_______________________________________________


I haven't yet found detailed public information about temperatures,
pressures, and durations of the complex turbulent blast jet on the surface.
_______________________________________________


Rich Murray, MA
Boston University Graduate School 1967 psychology,
BS MIT 1964, history and physics,
1943 Otowi Road, Santa Fe, New Mexico 87505
505-501-2298 rmforall at comcast.net

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Received on Sun 27 Feb 2011 03:15:38 AM PST