On Feb 21, 4:22 am, Tux Wonder-Dog <wes.par...@[EMAIL PROTECTED]
> wrote:
> Logan Kearsley wrote:
> > On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@[EMAIL PROTECTED]
> wrote:
> >> John Park wrote:
> >> > Dave Farrance (DaveFarra...@[EMAIL PROTECTED]
) writes:
> >> >> Logan Kearsley <chronosur...@[EMAIL PROTECTED]
> wrote:
>
> >> >>>World Idea #1: A tidelocked planet orbiting a red dwarf. The
> >> >>>temperature goes above freezing at the substellar point, maybe
leading
> >> >>>to the formation of lakes or a small sea, otherwise just increased
> >> >>>sublimation that keeps it relatively ice free. Question- do
glaciers
> >> >>>across the hemisphere creep towards the substellar point, or would
it
> >> >>>be more likely that the whole above-freezing region would remain
ice-
> >> >>>free, with mostly-static icesheets thickening as you get further
away?
> >> >>>Or something else entirely?
> >> >>>Over on the dark side, temperatures get too cold even for the
natives
> >> >>>to find comfortable but there's no sunlight anyway, so it doesn't
much
> >> >>>matter. Perhaps there's a CO2 icecap around the antistellar point?
>
> >> >> I don't know enough about planet formation to comment on World
Idea
> >> >> #2, but the problem with the above idea is that it will get *very*
> >> >> cold on
> >> >> the darkside. The entire atmosphere except for any helium would
> >> >> freeze
> >> >> out. The water would also eventually find its way around to the
> >> >> darkside via sublimation.
>
> >> > Wouldn't that depend a bit on how thick the atmosphere was and how
> >> > efficient its wind system was in moving energy around? (As far as I
> >> > know, despite its slow rotation--and because of its thick
> >> > atmosphere--Venus has no significant temperature difference between
its
> >> > day and night sides.)
>
> >> It very much depends on the atmosphere's density and its composition.
>
> >> You would have a "hot spot" which would shift with libration
(precession?
> >> as
> >> well?). This would create at least one atmospheric cell - in the
form of
> >> a static cyclone.
>
> > I have never had this adequately explained- some of the simulations
> > result in two cyclones, mirrored across the equator, and others result
> > in a single cyclone. In the single cyclone case, what determines the
> > direction of rotation?
>
> I think it would be the libration that would determine the direction of
> rotation. It'd be heating an area that would shift within a few degree
per
> orbit, and the effect would be the same as swinging a stone on the end
of a
> string.
As far as I can tell, libration wasn't included in the simulations.
> Could someone who knows a bit more than I do, explain the two cyclone
> concept? The only reason I can think of why there would be two cyclones
is
> that there is still more rotation in the system than should be in a
> tide-locked planet. And thus there is still a north/south-hemisphere
> atmosphere ...
How much 'should' there be? It is what it is. I suspect that's a large
part of what's happening.
Or, an alternate explanation might be that I'm horribly
misinterpreting the graphs. I don't *think* I am, but I'll throw it
out there as a possibility, 'cuz the article never actually mentions
cyclones; one must infer them from the temperature and pressure plots.
> > And what happens when the planet's rotational period is significantly
> > longer than 24 hours?
>
> The planet is tidally locked. If its rotational period was 24 hours
long,
> it would be very close to its sun - I suspect almost within its
> photosphere. And no star has its ecosphere/Goldilocks zone that close.
By
> definition its rotational period is longer than 24 hours.
I wrote imprecisely. By 'significantly', I was thinking 'several
orders of magnitude'; the period used in the article for a .1 solar
mass star was ~8 days. They actually did most of the simulations with
a .5 solar mass star and rotation rate similar to Titan, which is
about 16 days. But what if it were, say, 100 days? Does it make any
difference?
-l.
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