On 17 Jul 2009 at 10:46, allen carpenter wrote:
> I actually had similar thoughts after I had heard about 'super-
> earths' a little over a year ago and DID have a brief email exchange
> with EDG. His expertise in the field pointed out at that time that
> the locations of known super earths put them out of range of the
> habitable zones either too close or too far. and in any event he
> pointed out the scientific aspects of atmosphere. specifically
> composition rather than density per se. an atmosphere too rich in O2
> wouldn't last long due to combustibility with other elements. O2 is
> less common than hydrogen and nitriogen anyway. so an atmosphere
> compromised of say %25 O2 at any density provides a combustion
> chamber for an atmosphere. even items which normally will not burn at
> %17 O2 WILL burn at %25. There is an argument that can be made that
> O2 will make it's own equilibrium in the long run when it 'burns
> off'. but that is one for EDG, not me. still, it would be interesting
> to have an adventure on a planet with an O2 content high enough to
> pose a hazard to a crew even in Hostile env. vacc suits. and oh yeah,
> O2 IS a corrosive at high enough concentrations. another one for EDG
> or a chemist perhaps.
You can't *get* significant amounts of O2 in an atmosphere without
"plants" *putting* it there.
And since even wet organic material will burn easily in a high O2
atmosphere, the first lightning strike will cause a major fire if the
O2 level gets that high.
> Perhaps terraforming will be the only way, in the long run, to find
> another earthlike atmosphere.
Or native life...
Likely pre-life atmosphere of a reasonably old planet (as opposed to
a young one that is still reaching equilibrium) is N2, H20, CO2.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com