Expert: Jayendra Upadhye - 2/6/2008

Question
could a 3,ooolb. 4ft. stone flying through the atmosphere for 3,ooo miles heat sufficiently enough to give it the differentiated composition giving the amount of time it took?

Answer
Hi,
I found your question lying in the pool and did not feel it was a homework question. (But then i could be wrong too).

Any way i thought it fit to answer.

Actually the average speed of the incoming matter is around 20 km/sec.
That would mean that time of travel in seconds would be
T = [(3000 miles * 1.6 km/mile)/20 km/sec] seconds
T = 240 seconds or 4 minutes.

A 3000 pound stone would not melt significantly in that time because:-1) - As the outer high temperature layers melted the layers immediately below, the supersonic air blast from the shock front would blow the molten material away.
    This would result in ablation (removal of surface material that actually carries away a lot of the acquired heat also, from the main body of the meteorite. (The shuttle uses ablative cooling when its tiles heat and "ablate").
read up ablatives on wikipedia.

2) - The thermal conductivity of rock will put an upper limit on how deep will the molten surface be, at any given moment.
The lower this figure, the shallower will be the depth of penetration of heat (molten layer). In good ablatives, this layer is fractions of mm deep!

3) - Conductive heat transfer will be greatly reduced as molten matter is actually removed continually by the shock front.
However an overall temp rise will be there throughout due to conductive transfer, as the ablating envelop will simulate an immersion of the meteorite in a bath of molten high temp rock for 4 minutes.

4 - For differentiation to occur, thee is an implied presence of a uniform gravitational gradient as inside large bodies such as protoplanets with molten cores. Small meteors lack this gradient as all points are at same gravitational potential. Even complete melting will still retain the different materials inside, in same relative locations. except may be spread them out by viscous forces, more evenly in their localized areas.

You may draw your own conclusions from the above.
Please do rate the answer if it helped you.
Regards.
Jayen

jp,
Thank you for the 10s!
But would greately appreciate if you could add a nomination to boot!
:)

That is the only "fee" i ask!

No i cannot tell you much more further, as i am not deep into metorites anyway.
Do write to me what transpires after the experts shows up and checks it out.
my mail-id is jupadhye_99@yahoo.com.
regards
Jayen