On 17 Jul 2009 at 14:58, DED wrote:
>> The fact that they *aren't* gas giants pretty much guarantees that
>> they were exposed to really high temps for an extended period to
>> drive off the volatiles.
>> That would tend to make them a lot les hospitable to life.
> Well, I know that in the one article they mention that three of them
> were quite close to the parent star so, yes, most,if notall, of the
> volatiles were likely baked off. Though, if they were further out,
> particularly in the habitable zone, why couldn't some of the
> volatiles still be left behind? Taking into account that these worlds
> are approx 4 to 9 times as massive as Earth, couldn't they be of
> sufficient size to hold onto enough of an atm? Could it be possible
> that the atmosphere is confined to valleys, thin and low as per Trav
> atm Type F?
The problem is that they'd hold on to *too much* atmosphere if they
didn't get "baked".
> Most of the gas giants that I've heard that were discovered have been
> listed as multiples of Jupiter's mass. I admit I haven't checked the
> full listings or consulted any frequency distribution graphs of
> exoplanet mass so I could be off.Yet we know from our own solar
> system that 14.5 Earth masses (Uranus)and sufficient distance from
> the parent star is enough to form a gas giant. Do we know where the
> dividing line is in terms of mass and distance from a starbefore a
> terrestrial world becomes a gas giant?
The core of jupiter (the part that's rock & metal, rather than
hydrogen) may mass *less* than 9 times Earth's mass.
Once you hit a certain point, capturing gass and dust from the nebula
the system is forming from *snowballs*.
It's easier farher out, as the solar wind and heating (and UV) from
the star won't drive off hydrogen nor break down hydrogen containing
compounds.
> We know that there are "hot Jupiters,"gas giants orbiting so close
> to their parent starts that Mercury seems like it's out in the
> bleachers. Even so, these worlds still retain atmospheres, albeit
> they are being boiled away. So is there an algorithm relating world
> and parent star mass, distanceand atmosphere loss over time?
The hot jupiters are thought to have formed a lot farhder out and
then "spiralled in" due to friction with the nebula during system
formation.
The "super-earths had to have been able to clect a *lot* of rock &
metal but *not* keep much gas. If they had, they'd be small gas
giants, because that's the way the relative abundance of volatiles
and non-volatiles goes.
So the odds *heavily* favor them having been "baked off".
> Putting this all together for Traveller, is there a way that these
> worlds can be usefullyincorporated into Traveller or are they just
> written off as chthonian planets
> (
http://en.wikipedia.org/wiki/Chthonian_planet)? Or, if they're far
> enough from their parent star, failed "ice giants" (Uranus and
> Neptune)? Considering their hypothesized frequency in the real
> galaxy, it might be nice to find a way to incorporate them into
> Traveller somehow.
Well, my vote is that they aren't going to have useful atmospheres,
because the baking effects mean that even if they had those deep
valleys, the gases would not support life because almost all the
hydrogen (and many other lighter elements like oxygen amnd nitrogen)
will have been driven off.
The one in the article with the "rock vapor" atmosphere ought to be
interesting as if it really does vaporize on sunward and condense on
"nightside" and it is a "oneface" world, then it's going to act like
a planet sized zone refining setup, concentrating the lower
vaporization compounds on nightside and the highder ones on dayside.
Mining dayside would be hell. Nightside likely isn't a lot better.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com