[meteorite-list] 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

From: Rich Murray <rmforall_at_meteoritecentral.com>
Date: Mon, 30 Aug 2010 00:05:49 -0600
Message-ID: <CA7FA7DB2585476BAE2875D9D80AE83A_at_ownerPC>

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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[ Rich Murray:
If the impactors came in with some initial spin, then may arise possible
vortex processes producing tornado-like jets with contracted diameters with
increased velocities, temperatures, pressures, and durations.
Also, smoke ring like structures might form from incandescent plasma
"pancakes", with intense complex spins.
Ground effects then might be extremely varied, as happens with tornados.

The militaries are inevitably going to consider these spin effects for new
kinds of projectile weapons.

The public has to be especially alert re the possibilities that new routes
to implosion might lead to new fission and fusion weapons with directed
energies.

Governments may try to keep the public out of the loop. ]


[ see also: http://en.wikipedia.org/wiki/Younger_Dryas_event ]

http://impact.arc.nasa.gov/news_detail.cfm?ID=179
[ Extracts ]

Tunguska Revision, and a Possible NEA Impact on Mars

Article Posted: December 21, 2007
A proposed downsizing of the energy of the 1908 Tunguska airburst implies an
increase in the expected frequency of such impacts.

(1) TUNGUSKA IMPACTOR SIZE REVISION

The 1908 Tunguska airburst from a small asteroid has generally been
estimated to have had an energy of 10-15 megatons. The corresponding size
for a rocky impactor is roughly 60 meters in diameter. Mark Boslough of
Sandia Laboratory, however, has generated new supercomputer simulations that
suggest a smaller Tunguska explosion. In part his models require less energy
in the explosion because he includes the substantial downward momentum of
the rocky impactor, rather then modeling it as a stationary explosion. If
this revision (down to an estimated energy of 3-5 megatons, and a
corresponding diameter perhaps as low as 40 m) is correct, the expected
frequency of such impacts changes, from once in a couple of millennia to
once in a few hundred years. If smaller impactors can do the damage
previously associated with larger ones, of course, the total hazard from
such impacts is increased. Below is a press release from Sandia and a
newspaper article discussing this new work.

David Morrison
------------------------------

(1a) SANDIA PRESS RELEASE: NEW ESTIMATE OF TUNGUSKA IMPACTOR SIZE

December 17, 2007
ALBUQUERQUE, N.M.

The stunning amount of forest devastation at Tunguska a century ago in
Siberia may have been caused by an asteroid only a fraction as large as
previously published estimates, Sandia National Laboratories supercomputer
simulations suggest.

"The asteroid that caused the extensive damage was much smaller than we had
thought," says Sandia principal investigator Mark Boslough of the impact
that occurred June 30, 1908. "That such a small object can do this kind of
destruction suggests that smaller asteroids are something to consider. Their
smaller size indicates such collisions are not as improbable as we had
believed." Because smaller asteroids approach Earth statistically more
frequently than larger ones, he says, "We should be making more efforts at
detecting the smaller ones than we have till now."

The new simulation - which more closely matches the widely known facts of
destruction than earlier models - shows that the center of mass of an
asteroid exploding above the ground is transported downward at speeds faster
than sound. It takes the form of a high-temperature jet of expanding gas
called a fireball. This causes stronger blast waves and thermal radiation
pulses at the surface than would be predicted by an explosion limited to the
height at which the blast was initiated.

"Our understanding was oversimplified," says Boslough, "We no longer have to
make the same simplifying assumptions, because present-day supercomputers
allow us to do things with high resolution in 3-D. Everything gets clearer
as you look at things with more refined tools."

The new interpretation also accounts for the fact that winds were amplified
above ridgelines where trees tended to be blown down, and that the forest at
the time of the explosion, according to foresters, was not healthy. Thus
previous scientific estimates had overstated the devastation caused by the
asteroid, since topographic and ecologic factors contributing to the result
had not been taken into account.

"There's actually less devastation than previously thought," says Boslough,
"but it was caused by a far smaller asteroid. Unfortunately, it's not a
complete wash in terms of the potential hazard, because there are more
smaller asteroids than larger ones."


Simulations show that the material of an incoming asteroid is compressed by
the increasing resistance of Earth's atmosphere. As it penetrates deeper,
the more and more resistant atmospheric wall causes it to explode as an
airburst that precipitates the downward flow of heated gas.

Because of the additional energy transported toward the surface by the
fireball, what scientists had thought to be an explosion between 10 and 20
megatons was more likely only three to five megatons. The physical size of
the asteroid, says Boslough, depends upon its speed and whether it is porous
or nonporous, icy or waterless, and other material characteristics....

http://www.planetary.org/programs/projects/targetearth/tunguska.html
[ Extracts ]

When a sizable rock rock enters the atmosphere form space it travels at
hypersonic speeds, and the air resistance it encounters causes it to
increase its diameter and "flatten out." This in turn increases the air
resistance even more, which causes even more flattening, and so on. The
overall effect on the asteroid as it streaks through the atmosphere is known
as "pancaking" because of the flat and thin shape that is inexorably forced
upon it.

Throughout this process the pancaking space rock heats up exponentially
until it fragments and vaporizes in a big explosion at a distance from the
ground known as the "airburst altitude." For the Tunguska Event Boslough
estimates this altitude at around 12 kilometers.

Now if an asteroid explosion were analogous to a detonating bomb, this is
where the story would end: the force of the explosion at the airburst
altitude would wreak havoc on the ground in exactly the same way as an
equally powerful bomb detonated at the same height.

But in fact, according to simulations run by Boslough and Crawford, this
initial explosion is only the beginning of the devastation brought on by an
impacting asteroid. As the space rock blazes through the atmosphere, it
leaves behind it a hot low-density wake of air mixed with rock vapor, which
can reach far behind the rock and shoot out into space.

Then, once it reaches the airburst altitude, the mass of the asteroid
fragments and vaporizes in a massive explosion, and takes the form of a
giant fireball of vaporized rock and air.

Even then -- and this is the chief difference between Boslough's and
Crawford's simulation and previous ones -- the fireball continues speeding
towards the ground, driving a massive shockwave before it. At this point the
fireball is moving much slower than the asteroid had been prior to the
explosion, but it is still traveling at supersonic speeds. And it is the
fireball and its accompanying shockwave, say the article's authors, not the
initial bomb-like explosion, which cause most of the damage on the
ground....

Impact at Tunguska

Boslough and Crawford ran repeated simulations of the Tunguska event, trying
to reproduce the scale of the devastation seen in the region. From this they
concluded that even if the airburst explosion took place at an altitude of
12 kilometers or higher, it probably had a magnitude of only 3 to 5
megatons. This is considerable less than the popular figure of 10 to 15
megatons, and less than 1% the high end suggestion of 700 megatons.

That such a comparatively small explosion could cause this much damage is
due to the fact that it was not a point explosion at the airburst altitude
that caused the damage, but the fireball and shockwave that continued moving
towards the surface. At a height of around 4 kilometers, the simulations
show, the fireball came to a stop, but the shockwave continued on. It was
the shockwave, not the explosion at the airburst altitude and not even the
streaking fireball, which was responsible for most of the devastation in the
forest.

Click to enlarge
http://www.planetary.org/image/NGmag.jpg
Tunguska asteroid simulation
Computer simulation of the Tunguska impact by Mark Boslough and David
Crawford of the Sandia National Laboratories in New Mexico.
Note the firey wake behind the asteroid, the point of explosion when the
fireball is formed, and the fireball continuing towards the surface.
The bluish outline marks the shockwave, which caused most of the devastation
in Tunguska.
Credit: M. Boslough/Sandia National Laboratories

Tunguska, in its way, was fortunate that it was spared direct contact with
the supersonic fireball, but in other times and places our planet was
undoubtedly scorched by by fireballs that made it all the way to the
surface. "There is an energy threshold," explained Boslough, "that separates
impacts in which the fireball comes to a stop in the lower atmosphere from
impacts in which the fireball actually hits the ground." The former are
Tunguska-like events, which leave no trace in the geological record, and the
damage they cause is erased within a few decades. Even the Tunguska event
itself would probably never have been known if it had not been witnessed,
and word about it disseminated through modern means of communication.

To the second type belong only those rare giant impactors who possess
sufficient energy to send a fireball hurtling all the way to the ground. In
those cases simulations show that the fireball can make direct contact with
the surface over an area of hundreds of square kilometers. At the point of
impact sustained wind speeds will exceed the speed of sound, and the
combined effect will melt the very rocks in the impact area.

Boslough and Crawford believe that just such an event less than a million
years ago may have been responsible for the strange deposits in Laos known
as Muong-Nong tektites. A similar fireball 29 million years ago, produced by
an asteroid around 120 meters in diameter, may have been responsible for the
striking-looking stones known as "Libyan Desert Glass."...

http://est.sandia.gov/staff/markb.html

https://share.sandia.gov/news/resources/releases/2007/asteroid.html

http://www.sandia.gov/videos2007/2007-6514Pavmag-tun3.mpg

"The hot fireball decends to the surface and slides downrange at high
velocities, subjecting the landscape to blast-furnace condtions."

Movie 3 (4.8 MB)
3D simulation of a 15 megaton explosion that is initiated 18 km above the
surface, for an asteroid entering at an angle of 35 degrees above the
horizontal.
Box dimensions are 40 km wide, 20 km high.
Colors indicate speed.
The hot fireball decends to the surface and slides downrange at high
velocities, subjecting the landscape to blast-furnace condtions.
This did not happen at Tunguska.


http://74.125.155.132/scholar?q=cache:YY6MFUns_CkJ:scholar.google.com/+%22Mark+Boslough%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.
_______________________________________________


excellent Google Earth and ground views of shallow oval craters worldwide,
Pierson Barretto: Rich Murray 2010.08.22
http://rmforall.blogspot.com/2010_08_01_archive.htm
Sunday, August 22, 2010
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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 Mon 30 Aug 2010 02:05:49 AM PDT