Logan Kearsley wrote:
> 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.
The study needs to be redone with it included, then.
>
>> 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.
Well, has anyone done an estimation/study of how long it would take for a
satellite to lose its angular velocity and become tidally locked?
(I confess I have always tied the Coriolis Effect to the fact that Earth's
angular velocity isn't synchronous with its orbital period. I would be
grateful for anyone to correct me on that.)
> 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.
Is it possible that I could _see_ this article?
> "Simulations of the Atmospheres of
> Synchronously Rotating Terrestrial Planets Orbiting M Dwarfs: Conditions
> for Atmospheric Collapse and the Implications for Habitability" by M. M.
> Joshi, R. M. Haberle and R. T. Reynolds
I don't have it in my hot little hands, and I could only see the abstract
when I visited the web-site. My email address is wes [dot] parish [at]
paradise [dot] net [dot] nz Thanks
>
>> > 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?
Not that I can think of, right off hand. The only reason why it might be
significant that occurs to me, is the eccentricity of the orbit. If the
orbit is nearly circular, the difference between the aphelion and
perihelion won't amount to much; if it is highly eccentric, it won't be
viable for Earth-standard life (or "life as we know it" ;) On the other
hand, it might well prove the "breath of life" for your aliens - general
overall torpor when the planet is at aphelion, time to party when the
planet is at perihelion.
>
> -l.
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