Hi, Darren, Doug,
OK, I didn't "do the math," and you can forget that, as it's a complex
simulation that's required;
the number of factors is staggering. I did do the "research," though, reading a
few (hundred) pages on
the theoretical models of icy rocky and gassy only bodies.
First, the existence of sub-Jovian, Jovian, and super-Jovian bodies in
close orbits at high
temperatures around other stars convinces me that a "hot gas giant" is a
possibility, since they
obviously exist!
John S. Lewis, who developed many of the early theoretical models of
structure for such bodies
back in the when, wrote a book on the new extra-solar worlds, "Worlds Without
End," and he discusses
the "hot" giants. These's no theoretical problem; they're "keepers."
Second, it is really difficult to "boil away" a planet like Darren first
suggested in his orbit
swapping example. Even a Plutonian sized body would merely evolve over many
millions of years, not
evaporate.
Third, these Plutonians I have been talking about are not all volatiles,
like so many who dislike
them suggest, not "giant comets." What I probably didn't make clear writing
about them is that they
are made from "primordial" planetesimals, the equivalent of condensing them
directly from the solar
nebula without any extensive thermal modification. In other words, they
accreted out where the nebula
was cool, about 160 K and below.
The solar nebula is, er, was 60% volatiles and 40% rock. The rock has
already formed out at 160 K.
as grains, dust, pebbles, chunks, etc. In low vapor pressure space, the water
(and uranium oxides,
oddly enough) condense and accumulate at 160's K. There is some accretional
heating and about 20% of
the volatiles were driven off as the bodies formed. The resulting planets are
therefore about 50%/50%
volatiles and rock. This is easy to determine when you can get a density for
these bodies where
possible and probably applies equally well to all or most of them.
The larger Plutonian bodies are certain to differentiate, leaving a rocky
core and a "volatiles"
crust and mantle. The use of the word "volatiles" is very mis-leading here. At
these temperatures and
pressures, they should be regarded as "cryogenic minerals," with a substantial
fraction of the
strength of the silicate minerals of rock.
A Plutonian body like 2003UB313 will achieve central pressures of 100,000
bar, or 1,500,000
lb/in^2. Ices have crystal structures that collapse nicely into each other at
far lesser pressures and
produce a resultant crystal that is very strong, rigid, tightly bonded, nearly
metallic in some cases.
Their phase diagrams are highly complex, not as simple as a mere rock's. (I
sneer at petrologists
here.) The interaction of the variety of these volatiles is even more complex.
The eutectic melting of ammonia and water mixtures will drive you crazy if
you study it long
enough, believe me. In other words, there is kind of weather possible on a
Plutonian body as close in
Jupiter's orbit, and obviously Titan is a place where you need an umbrella AND
a warm coat and are
encouraged not to jump in the methane puddles (too cool for ammonia/water
weather).
The Jovian moons are the model of what a Plutonian world would be like.
Pluto is just Ganymede
(bigger than Mercury) cooled down to 109 K. Next is a really obvious point
seems to elude a lot of
heavy thinkers. Jupiter and the other gas giants did not capture every
Plutonian world; some, probably
most, escaped, ejected into the outer system. Now, which ones got away: the
little ones or the big
ones? Doh.
Yes, even the biggest gravitational fisherman of all, Jupiter, had "the big
one(s) that got away"!
That's BIGGER than Ganymede, Europa, Callisto, Io. Maybe the Jovian satellites
formed in place; maybe
not. I say not. All the other gas giant moons look like captures -- them too,
sez I. This is not say
that the Plutonian bodies accreted at 5 AU, only that that's the minimum
distance. They could (and
presumably did) accrete anywhere out from there, although exactly where is a
mystery for a while.
This why one could be (and still can be) confident of finding large outer
system bodies like
2003UB313 and its undiscovered and still larger companion planets. I said
"planets," IAU. It should
not have been a surprise! It probably was not to the successful searchers, but
a certain number of
minds seem to be struggling with reality here.
Hey, wait, you say, Jupiter's moon IO is not "Plutonian"! Ah, but it is.
You take a 50/50 ice/rock
Plutonian body, tidally heat it for billions of years, drive off the water and
other volatiles slowly.
The hot water reacts with the abundant sulfides in the solar mix which are
converted to sulfur and
sulfur oxides, too heavy to escape. You are left with the rocky core (80% of
the original diameter)
covered with bubbling sulfur circuses!
THIS is the answer to Darren's original question: what would happen if you
took Pluto or 2003UB313
and put them in Mercury's orbit or Venus' orbit. Darren, you have accidentally
discovered the secret
formula for making an IO!! You've just stumbled on to the KFC "original
recipe," or forced the dog to
spill the bean recipe!
As for hot gas giants, Uranus or Neptune could retain a lot for a lot
longer; their high densities
suggest a substantial rocky core. Jupiter's core is problematical and small if
there is one, but its
gravity is working just fine, thank you. Saturn, at a density of 0.68, is
probably all-volatiles but
that makes no difference.
However, though life would change some on a hot dry gas giant, much (most)
of the gas is retained
easily. Above 350 C, all water is removed from the atmosphere and surface and
the atmosphere becomes
transparent, bright and clear, but life goes on anyway without the previous
gloom.
Heat is NOT a problem for gas giants. The planet's oceans of pressurized
fluids (and solids) are
very hot anyway. Jupiter's core temperature is 20,000 C or more!! Only the very
outer layers of a gas
giant are cool, a thin cooled skin or scum formed over the inferno raging
beneath, which radiates away
more heat from the planet in Jupiter, for example, than Jupiter receives from
the Sun. If you think
Venus is Hell, try again.
The "cool and distant" gas giants of our mind's eye are in fact the hottest
worlds in the solar
system already. The interiors of a Plutonian world are probably similar to the
core temperatures of a
comparably sized Terrestrial world, possibly even hotter, as there are
indications that more
radioactive isotopes would be present, persist longer, and contribute more to
heating than in a
Terrestrial world.
Darren Garrison wrote:
> On Wed, 3 Aug 2005 20:12:01 EDT, [EMAIL PROTECTED] wrote:
>
> >Darren, if we swapped Uranus with Earth something similar to what you
> >envision might happen to Uranus at 1 AU as well...though your point is a
> >good one
> >to mull over...
>
> I haven't done the math on it (and to be honest, would have to do a bit of
> brushing up before I
> COULD do the math) but I was thinking that the Jovans had enough gravity to
> hold their atmospheres
> even at 1 AU temperatures. Think about all of those "hot Jupiters"
> discovered over the past few
> years. Anyone know the mass limit for a Jovan to keep it's volitiles?
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