Nevertheless, the Earth would have long ago cooled to a solid interior were
it not for the continued production of interior heat from radioactive decay.
There is more to it than simply the radiative loss of the heat of formation.
This is also a factor in the cooling rate of smaller bodies that are
responsible for iron meteorites. That is, even small bodies cooled slower
than might otherwise be expected, because of active internal heating from
radioactive decay (something that I think was touched upon earlier).
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "Darren Garrison" <[email protected]>
To: <[email protected]>
Sent: Saturday, September 05, 2009 11:01 PM
Subject: Re: [meteorite-list] Slow cooling rate of irons in space
Something I don't think anyone has touched on in this thread yet is that
the
heating and cooling of objects in space doesn't work the same way we, as
highly
modified fish living on the floor of an ocean of air, take for granted.
Heat is
transferred in three ways-- conduction, convection, and radiation.
Conduction
is what happens when two objects are in physical contact. Convection is
when
heat is circulated by a fluid, such as air or water. Radiation is when
heat is
transferred by infrared light.
We experience all three all the time. But for an object in
space-including a
planet like Earth-- the only way to cool down is by radiation. Objects in
space
aren't touching other objects and they aren't immersed in a fluid (vacuum
is the
best possible insulator) so an asteroid or a planet is going to cool much
more
slowly than what we would intuitively expect from our own experiences.
The
Earth is still almost all liquidish except for a thin skim of rock on the
very
outer rind-- and will probably be consumed by the dying sun LONG before
there
will be time enough to cool to the core.
When on a spacewalk, an astronaut's risk isn't getting too cold (even in
the
shadow of the Earth.) It is getting too hot-- the heat generated by their
own
bodies can't radiate away fast enough.
Touched on by others was that the bigger an object is, the slower it
cools, but
I don't think anyone explained it. An object can only cool through it's
surface. But with a sphere (or any given fixed shape) when size
increases,
volume increases faster than surface area-the bigger an object is, the
less
proportionate surface area it has from which to loose heat. (This applies
to
organisms, too-google "gigantothermy.")
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