[meteorite-list] Slow cooling rate of irons in space

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sun, 06 Sep 2009 00:01:50 -0500
Message-ID: <lke6a514vh5bo5mtgrvb8o0vsi20v4mjdh_at_4ax.com>

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.")
Received on Sun 06 Sep 2009 01:01:50 AM PDT