Q: Red giant heating effects on earth-like planets over time

[water as a greenhouse gas]

In article ,
(Steve Willner) writes:
I know virtually nothing about climate models, so I don't know what
effect the water vapor continuum really has. I suppose it competes
with cloud formation, which would decrease the incoming solar energy.

On thinking about this a little more, another property of water vapor
is that it is mostly confined to the troposphere (because the vapor
pressure drops so fast at low temperatures). See above about my lack
of expertise, but I think this property may tend to make water vapor
less effective as a greenhouse gas.

If there is somebody around who actually knows the answer, please
post!

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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In article ,
(Harmon Everett) writes:
And IIRC, [the Sun] only swells up because of excess silicon and iron waste
products, even though it still has 90% of its usable hydrogen fuel
left. So removing the silicon and iron waste products is just an
engineering problem, which we ought to be able to solve sometime in
the next 2 or 3 billion years before it happens. Piece of cake.

It's actually the growth of a hydrogen-depleted, helium-rich core
that leads to a red giant. If you could remix hydrogen into the
core, you could keep the Sun on the main sequence longer, though not
forever. I don't think the fraction of fuel left when the red giant
phase starts is anywhere near 90%. Of course the Sun's luminosity
will still increase.

Probably easier than mass migration to another solar system.

Doubt it. We almost have the technology for interstellar travel
right now. I haven't a clue how one could mess with the Sun's
interior.

Other options are moving the Earth's orbit outwards (easier than you
might think, if you aren't in a hurry) or building O'Neill habitats
in distant orbits. These only buy small amounts of time, though.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner wrote:

In article ,
(Harmon Everett) writes:
And IIRC, [the Sun] only swells up because of excess silicon and iron waste
products, even though it still has 90% of its usable hydrogen fuel
left. So removing the silicon and iron waste products is just an
engineering problem, which we ought to be able to solve sometime in
the next 2 or 3 billion years before it happens. Piece of cake.

It's actually the growth of a hydrogen-depleted, helium-rich core
that leads to a red giant. If you could remix hydrogen into the
core, you could keep the Sun on the main sequence longer, though not
forever. I don't think the fraction of fuel left when the red giant
phase starts is anywhere near 90%. Of course the Sun's luminosity
will still increase.

Are there any suggestions on where to look for the time it takes for
this stuff to happen?




--
"The rabbits became strange in many ways, different from other rabbits.
They knew well enough what was happening. But even to themselves they
pretended that all was well, for the food was good, they were protected,
they had nothing to fear but the one fear; and that struck here and
there, never enough at a time to drive them away. They forgot the ways
of wild rabbits. They forgot El-ahrairah, for what use had they for
tricks and cunning, living in the enemy's warren and paying his price?"
-+ Richard Adams, "Watership Down"