[extropy-chat] Scientists Confront 'Weird Life' on Other Worlds

[Robert J. Bradbury]

On Thu, 13 May 2004, Mike Lorrey wrote:

> Can anyone think up how a carbon scarce but silicon rich planet might
> form?

Its normal melting point condensation.  Some of the most abundant
elements you have in a solar nebula are C, O, and Si (actual solar
comp is H > He > O > C > Ne > N > Mg > Si > Fe > S) but this will
vary a fair amount from star to star [Mike if you have my ssmass.xls
spreadsheet you want to look at the SSComp sheet.  If you don't have
it send me an offlist note and I'll send you a copy.]

The Si/Mg oxides are going to condense out close to the star.
The C oxides (CO & CO2) are going to condense out much further
away from the star (read comets for the most part).  So if the
planets are not large enough to serve as good comet targets (e.g.
Venus & Earth -- to a lesser extent Mars) and/or lack the gravity
to hold onto CO & CO2 in gaseous form and/or you get some Jupiter
type planets capturing or hurling comets out of the system then you
get planets in the liquid water zone that tend to be carbon poor
and Si/Mg rich.  (I chose to discuss Si because it can form 4 bonds
while Mg can typically form only 2).

Also Mike, if you have my PhysProp.xls spreadsheet and look at the
BondStrength sheet you will see (if I'm interpreting it correctly
that the C-C bond strength is almost identical to the Si-Si bond
strength so I'm not quite sure why carbon is the basis for organic
life while silicon is the basis, in part, for geochemistry (and
semiconductors...).  A puzzle perhaps.

Robert