Re: Steam World


Logan Kearsley kirjutas:
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Logan Kearsley kirjutas:
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On May 8, 6:10 pm, "Logan Kearsley" <chrono.sur...@xxxxxxxxxxx> wrote:
Say that a planet's oceans are boiled, but for whatever reason it does not
turn into a Venusoid inferno. Instead, you've just got an atmosphere full of
steam, not too far from condensation, with little or no pure liquid water on
the surface.
[...]
First question: how could that come about?

For this to be a stable situation you need to have the mass of the
planet be a lot higher than that of the earth such that it does not
rapidly lose the H2O to space, then the heat balance needs to be right
so I think that is going to put it inside the habitable zone, as if it
is near condensation, H2O is a WONDERFUL radiative gas in that it is
very "black" in the IR meaning it will dump heat to space fast so you
need to be putting in heat just as fast or you wind up with a liquid
water surface and much lower temperature.

Outer edge of the usual habitable zone, or a little beyond, I was thinking-
you probably want less heat coming in that Earth gets, since water is> such a
fantastically good greenhouse gas (being a good radiator, it's also a good
absorber). But the trouble then is, how do you get the initial pulse of heat
out there that would cause the oceans to evaporate in the first place?
A nearby supernova or CME was suggested; but that sort of feels like
cheating (no, I don't know why; I suppose it's a perfectly good suggestion,
I just want others). Here's a thought- could pent-up volcanism do it? Say, a
Venus-like resurfacing event? Thick crust traps heat in the interior and
doesn't let it off through plate tectonics, and eventually large sections of
the crust just melt straight through, and everything on the surface gets
vaporized. I don't know how realistic that actually is.

What about tidal evolution?

Imagine Io with the size and position of Mars, or slightly more. It is
tidelocked to the primary, and orbits slower than the primary. So, the
tidal friction in the primary ensures the secondary has slowly
expanding orbit, while tidal friction in the secondary keeps the
secondary orbit nearly circular and the tidal heating there limited.
Now, the next outer satellite, Europa, has slightly more than twice
the orbital period of Io initially - with the tidal evolution, both Io
and Europe have increasing period, but Io being closer and having more
tidal friction would evolve faster and thus the ratio of period
decreases. When the ratio decreases to 2, Europa and Io enter 2:1
resonance, the orbit of Io gets much more eccentric, and the tidal
heating increases hugely.

Could tidal heating produce enough power to heat the surface to
ocean-boiling temperatures?

You started by saying not a Venus-like inferno. A steam atmosphere not
Venus-like inferno and little liquid water implies not enough for an
"ocean".

One would need an exceptionally large gas giant to get a Mars-sized moon,

Have seen that argument. But not awfully convinced.

plus a second moon large enough to have a sufficiently large effect on its
orbit, and I really have doubts about managing a moon large enough to hold
onto a water vapor atmosphere; unless perhaps it was captured after
formation....

Why?

Anyway, if the formation of steam atmosphere was recent then you can
allow for losses.

Titan holds onto an atmosphere with a lot of methane.

.

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