Re: Planetary gravity question.

On Sun, Aug 04, 2002 at 11:34:17AM -0700, Johan B?jeryd wrote:
>[Laserlight wrote:]
>> If you took an Earthlike
>> planet and knocked
>> most of the lighter layers off the top, that would
>> be about right,
>> more or less, approximately.

I fear not. Earth's density is about 5.515 g/cm^3 - about the same as
iron, because it has an iron core. Fair enough. This hypothetical planet
would have a density of about 20.2 g/cm^3 (radius x density is constant
for constant surface gravity, radius of moon is about 1737.5km, radius
of Earth is about 6371.01km).

For reference, pure gold has a density of 19.32 g/cm^3; platinum is 
21.3; iridium is 22.16. Within reasonable error tolerances, we're 
looking at a solid lump of precious metals 2,000 miles across.

>> I think the
>> atmospheric density would
>> drop off a lot faster than it would on Earth,
>> though--you'd have have
>> mountain peaks in semi-vacuum.

This is a non-trivial calculation. :-)

>I knew that it depended on mass but now thats
>confirmed... :)
>Would the inclusion of denser materials and metals
>make the soil toxic in any way?

Very much so! (At least to humans and things in the human food chain.)

>I suppose that a planet which is this dense would a
>lott more profitable (with richer finds) to mine?

Yup. Mining colony, almost certainly with most of its food shipped in
from
elsewhere.

Roger