[meteorite-list] Meteoroid/Asteroid Electro-Magnetic Disruption and Charge Properties?

From: Pict <pict_at_meteoritecentral.com>
Date: Wed, 27 Feb 2013 11:52:11 -0700
Message-ID: <CD538FB5.12D27%pict_at_pict.co.uk>

Chris,

Working on oil and gas wells it is routine to test the fracture point of
the rock at the bottom of the well after having run and cemented a casing
string (leak off test). You do this by shutting in the well at surface and
pumping incremental volumes of mud into the hole and noting the rise in
surface pressure with each injection. When the rock is behaving
elastically the rise in pressure is linear with volume, but you can see
when the rock has reached its elastic limit when the pressure increase
with volume becomes less. This occurs at the onset of fracture generation,
and continued pumping typically results in extensive fracture propagation
and an actual lowering of surface pressure as it is dissipated by mud
flowing into the fractures. Same principal is employed with hydraulic
fracturing to increase production surface from low permeability
lithologies (shale etc).

Empirically testing the fracture point of the rock gives you a handle on
the maximum mud density the well can sustain when drilling the next hole
section, and the maximum pressure one could hold at surface with the BOP
in the event of encountering formation pressure in excess of the mud
hydrostatic. If you exceed the fracture pressure by increasing the mud
'weight' (density) to control formation pressure, the danger is you induce
fractures, lose height in your your mud column as it drains into the
wellbore thereby reducing hydrostatic pressure at the bottom of the well
and thereby risking falling below the formation pressure inducing the well
to flow (kick) or blowout in the worst case. Shutting a flowing well in
with the BOP when the formation pressure is higher than the mud
hydrostatic (I.e. Flowing) you ideally do not want the surface pressure
plus the mud hydrostatic to exceed the 'leak off' as then you run the risk
of an underground blowout where the high formation pressure flowing zone
breaks down a weaker zone (generally higher up) and flows formation fluid
(oil/water/gas) into it displacing the mud present between the two zones.

I apologise for the off topic background above but I am wondering if the
disintegration mechanism is analogous for a meteor. The pressures you
quote at the leading surface of the meteor are in the typical range I
would expect from the well experience. Presumably the pressure at the rear
is relatively low, and the pressure cannot dissipate around the object due
to the speed of entry exceeding the speed of flow of compressed air around
it. So if this pressure differential is applied to the front of the object
there must come a point where the elastic limit is breached, fractures are
induced, and then rapidly propagate. Once there are multiple paths of
pressure communication through the former solid object rather than around
it, there is presumably a rapid lowering of differential pressure from
front to rear occurring as air rushes through the gaps between the
fractured pieces and expands as the pressure lowers towards the rear of
the disintegrating meteor pushing everything apart (I.e. Exploding). As
Chris says this also vastly increases the surface area for incandescence
and the the luminosity might be expected to greatly increase. I am
wondering if this is at all a realistic description of what might be going
on?

I am unsure of the temperatures involved at the leading edge and in any
case I can't find phase properties for water at those extremes, but also
wonder if water exists as a liquid or gaseous phase at the leading edge or
is it entirely plasma?. I'm sure the pressure would take it past the
dewpoint but is the elevated temperature sufficient to prevent
condensation at some point so that a liquid 'injection' phase forms at
some point during disintegration and collapse of the initial pressure
differential? Condensed water seems evident in the trail judging by white
colour evident in some 'smoke trails'.

Are there any published properties for typical
chondrites/irons/mesosiderites available (e.g. Porosity, permeability,
Poisson's ratio etc), and have any destructive pressure experiments been
conducted to determine failure mechanisms for these materials?

I presume the ductility inherent in irons versus the brittle nature of
chondrites results in disintegration along far fewer planes of fracture,
generally resulting in larger pieces after failure.

Regards,
John


On 27/02/2013 09:21, "Chris Peterson" <clp at alumni.caltech.edu> wrote:

>A body larger than about a centimeter transfers its kinetic energy to
>other forms primarily by compressing the air in front of it as it
>descends into the atmosphere. The pressure involved is typically very
>large- tens or hundreds of megapascals for meter-class bodies. Once this
>ram pressure exceeds the material strength of the body, it breaks apart
>(presumably along existing fault lines, so the material properties of
>the body are important- and generally unknown).
>
>Before the breakup, the heat created by compressing air is melting the
>surface of the meteoroid, resulting in ablation. This ablation is
>responsible for some of the light we see (along with atmospheric
>ionization from the same heat source), but is not particularly
>disruptive to the meteoroid. Only the outer surface is affected.
>Ablation is a very efficient way of removing energy (which is why
>spacecraft heat shields prior to the shuttles were ablative). When the
>meteoroid fragments at hypersonic speeds, however, additional surface
>area is instantly exposed, resulting in a rapid heating of the
>surrounding air (which is just a fancy way of saying "explosion"). If a
>body breaks into just a few pieces, as is common, we may see a central
>or terminal brightening. If it completely shatters into thousands of
>pieces (as seems likely with Chelyabinsk) the energy from the suddenly
>heated air is immense- an efficient conversion of kinetic energy to
>thermal energy. The expanding hot air can produce an impressive sonic
>wave, and probably further disrupts the meteoroid itself.
>
>I don't that there are any electrical forces of a significant size to
>affect the structure or motion of the meteoroid, although atmospheric
>electrical effects probably occur (e.g. electrophonics).
>
>Chris
>
>*******************************
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
>
>On 2/26/2013 11:59 PM, drtanuki wrote:
>> Dear List,
>> If there is anyone willing to discuss the how and why
>>meteoroids/asteroids "detonate" please explain for the list and myself.
>>I am interested learning more about the electrical/mechanical/physical
>>forces that these bodies undergo as they reach the earth such as in the
>>latest Russian event. Thank you.
>> Dirk Ross...Tokyo
>
>______________________________________________
>
>Visit the Archives at http://www.meteorite-list-archives.com
>Meteorite-list mailing list
>Meteorite-list at meteoritecentral.com
>http://six.pairlist.net/mailman/listinfo/meteorite-list
>
Received on Wed 27 Feb 2013 01:52:11 PM PST