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

From: Pict <pict_at_meteoritecentral.com>
Date: Wed, 27 Feb 2013 15:41:33 -0700
Message-ID: <CD53D133.12E3B%pict_at_pict.co.uk>

Chris,

there are indeed obvious differences. However, typically in leak-off tests
you are applying pressure to a relatively small area, maybe inside a
cylinder 6ft long and 1ft in diameter (you might typically drill 2m of new
formation below the casing shoe prior to the test). The rock is however
prestressed by the overburden load and formation pore pressure so that
needs to be overcome to an extent before 'expansional' stress is applied
to the matrix itself. Once the 'preloading' is overcome however, I think
perhaps it is an analogous situation - a small volume of rock with a
significant stress gradient across it. I really was wondering what happens
to the pressure distribution around the meteor when a multitude of
fractures rapidly propagate through a monolithic body offering additional
pathways for pressure equalisation front to rear, and if the resulting
redistribution of pressure through these fracture pathways could be a
mechanism to change a solid body into a dispersed cloud of rubble (i.e.
Blow it up) rather than a fragmented rock continuing in tight formation.
I'm sure it's a complicated scenario to model. Alternatively, the vastly
increased surface area from the near instantaneous formation of a
multitude of pieces might be the cause because of a sharp rise in drag
drastically augmenting thermal dissipation of kinetic energy. Seems an
equally plausible explanation within the confines of my imagination.

Regards,
John

On 27/02/2013 12:58, "Chris Peterson" <clp at alumni.caltech.edu> wrote:

>Hi John-
>
>I don't doubt that there are analogs between the fracturing you describe
>at the bottom of a well and what happens with a meteor. However, there
>may be some fundamental material differences. The rock at the bottom of
>the well is typically very large compared with the area where pressure
>is applied, and is already under high pressure. A meteoroid may range
>from nearly monolithic (particularly in the case of an iron body) to
>something like a rubble pile. Obviously, the response to a non-isotropic
>force from ram pressure will be very different in those cases.
>
>I'm not sure what happens to water during meteoritic flight. Most meteor
>trails are largely composed of dust, but if water trails are observed, I
>suspect they are largely produced in the same way that many airplane
>contrails are- the condensation of existing atmospheric water vapor onto
>solid particles, particularly in response to aerodynamic effects such as
>vortex production.
>
>There is lots of published information on the material properties of
>meteoritic material, but that is only of limited value in explaining the
>behavior of meteors, since the microscopic bulk properties are largely
>unrelated to the material properties extended over a meter-class or
>larger body. This is why we don't usually know much about the class of
>material producing a large fireball until an actual recovery is made.
>The fireball observations alone simply aren't enough. In fact, the best
>information on possible material comes not from how the meteor breaks
>up, but from the deceleration profile and mass estimates.
>
>Chris
>
>*******************************
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
>
>On 2/27/2013 11:52 AM, Pict wrote:
>> 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
>
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Received on Wed 27 Feb 2013 05:41:33 PM PST