[meteorite-list] Giant Asteroid Fragment Makes Impact

[Larry Lebofsky]

Hi,

Why does the impactor need to have been one piece when it hit or even before 
it entered the atmosphere?


Larry

Quoting Ron Baalke <baalke at zagami.jpl.nasa.gov>:

> > 
> > Hi,
> > 
> >     The rational for survivor fragments of an impactor is
> > that they are from the far back side of the impactor. The
> > transformation of the impactor's mass from a solid to a
> > plasma proceeds from the "front" or impacting surface.
> > A shock wave from this explosive vaporization preceeds
> > the actual transformation, traveling at the impact speed
> > of the body plus the rate of expansion of the vaporization.
> > If this shock wave speed exceeds the speed of sound in
> > the impacting body, the shock wave will fracture, pulverize
> > and even vaporize (if it's fast enough) the body of the
> > impactor ahead of it.
> 
> Another possibility is the meteorite fragment they found was from
> another fall, and not from the impactor that created the crater.
>  
> >     The models say the transient crater is deep, but it would
> > shallow up dramatically from rebound and ends up as
> > an extremely shallow crater for its size. If there was
> > little shock melting, is it possible that rebound melting
> > occured? Or the release of local vulcanism? I don't know
> > if we know enough about this crater to be sure.
> 
> 
> Bear in mind a lot can happen geologically in 144 million years since
> the crater was formed, not to mention erosion effects.  The depth 
> the crater is at today is probably not the depth it was when it was 
> created.
> 
> Ron Baalke
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