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

[Chris Peterson]

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" <cynapse at charter.net>
To: <meteorite-list at meteoritecentral.com>
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.")