I've got an idea for some neat aliens, but they need a world to live
on.

Average global temperature needs to be a good deal below freezing
(these particular aliens are most comfortable between about -40 and
-30 Celsius, and can survive being frozen solid), so that the vast
majority of water on the planet is in the form of icesheets. Global
high temperature of maybe 5 Celsius (excluding volcanoes), so that
liquid water does exist but is rare. Question- if the total amount of
water available per surface area was comparable to Earth, would
anything like ocean basins happen? Or, if one started out with ocean
basins, what would happen if they were to be frozen solid?
The atmosphere has very little if any free oxygen, so no ozone layer.
Beyond that...

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?

World Idea #2: A larger Mars gets whacked at an odd angle by a moon-
forming impactor, and ends up with a severely tilted axis. Somehow it
needs to avoid accumulating a thick CO2 atmosphere, and also avoid
losing most of its water- how? Is just being Really Cold sufficient to
hold onto a small ocean's worth of ice for sufficiently many billions
of years? Spring and fall feature balmy highs of -30C, with summer at
the poles maybe getting all the way up to freezing point, and winter
resulting in the condensation of polar CO2 icecaps. Exposure of the
icecaps to sunlight come spring results in semiannual mass airflow
from one hemisphere to the other, possibly resulting in global storms.

Thoughts?

-l.

On Feb 17, 11:03 am, Logan Kearsley <chronosur...@gmail.com> wrote:


> Thoughts?

This sounds very similar to "Snowball Earth", a theory that involves
super-ice-age conditions in the late Precambrian period.

http://en.wikipedia.org/wiki/Snowball_Earth

Take a look at that model temperature graph on the right: most of the
Earth has temperatures below freezing, though there's a band around
the equator that's warmer.

If you have half an hour, this site gives a good back-and-forth of
arguments for and against it:

http://www.snowballearth.org/

But whether or not the Earth was ever in such a state, it seems like a
plausible condition for an otherwise Earthlike planet. (Albeit one
around a slightly cooler sun; back in the Proterozoic, the Sun was
5%-10% less luminous than it is today.)

One other problem is that Snowball Earth would have been a temporary
state, lasting only some tens of millions of years. But that could
probably be handwaved too.


Doug M.

Logan Kearsley <chronosurfer@gmail.com> 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.

--
Dave Farrance

sigidu...@yahoo.com wrote:
> On Feb 17, 11:03 am, Logan Kearsley <chronosur...@gmail.com> wrote:
>
>
> > Thoughts?
>
> This sounds very similar to "Snowball Earth", a theory that involves
> super-ice-age conditions in the late Precambrian period.
[...]
> One other problem is that Snowball Earth would have been a temporary
> state, lasting only some tens of millions of years. But that could
> probably be handwaved too.

Similar, but not identical. It needs to be a permanent condition, so
there's at least a good billion years with large areas illuminated but
in deep freeze. If the planet is geologically active, carbon dioxide
will build up until it causes the Snowball Earth to melt. As I said
for idea #2, there needs to be some reason why that sort of thing
can't happen. I think it can be handwaved for idea #1 by saying that
higher CO2 pressure just causes more CO2 to precipitate out on the
antistellar cap, but that's not an option for #2.

-l.

On Feb 17, 11:55 am, Dave Farrance
<DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk> wrote:
> Logan Kearsley <chronosur...@gmail.com> 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.

Water finding its way to the darkside isn't a problem, as long as
there's enough of it. Glaciers will eventually creep back across the
terminator, so water cycles back and forth.
As for the atmosphere freezing out, that can only happen if there's no
substantial atmosphere to begin with. Otherwise, air will transport
enough heat from the lightside to the darkside to prevent itself from
freezing. Or even liquifying, most likely, but that gives me a cool
idea for a completely different world- could one get nitrogen rain on
the darkside of a tidelocked world, that then runs in rivers back to
the lightside, evaporating along the way?

-l.

Dave Farrance (DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk) writes:
> Logan Kearsley <chronosurfer@gmail.com> 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.)

--John Park

Logan Kearsley wrote:
> sigidu...@yahoo.com wrote:
>> On Feb 17, 11:03 am, Logan Kearsley <chronosur...@gmail.com> wrote:
>>
>>
>>> Thoughts?
>> This sounds very similar to "Snowball Earth", a theory that involves
>> super-ice-age conditions in the late Precambrian period.
> [...]
>> One other problem is that Snowball Earth would have been a temporary
>> state, lasting only some tens of millions of years. But that could
>> probably be handwaved too.
>
> Similar, but not identical. It needs to be a permanent condition, so
> there's at least a good billion years with large areas illuminated but
> in deep freeze. If the planet is geologically active, carbon dioxide
> will build up until it causes the Snowball Earth to melt. As I said
> for idea #2, there needs to be some reason why that sort of thing
> can't happen. I think it can be handwaved for idea #1 by saying that
> higher CO2 pressure just causes more CO2 to precipitate out on the
> antistellar cap, but that's not an option for #2.

A while back I read the 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
(<http://dx.doi.org/10.1006/icar.1997.5793>) and IIRC the simulations
they used suggested that as soon as the antistellar pole of a
tide-locked world got cold enough for carbon dioxide to freeze out the
atmosphere would permanently "collapse" into a frozen state because all
the greenhouse gas that could potentially warm it back up again would
get trapped there.

There were some interesting speculations about how stable some planetary
atmospheres might be. For example, M dwarfs often have extreme starspot
activity, and large persistent starspots can reduce the insolation a
planet receives by a consider amount over a timescale of months. In some
cases this could be enough to cause enough CO2 to freeze out on the far
side of the planet to permanently flip it over into an iceball state. In
the less extreme case where a planet is merely cold enough for all the
water to permanently freeze out into an icecap on the antisolar pole,
the lack of liquid water puts a stop to carbonate sequestration and CO2
starts building up in the atmosphere until the icecap melts again.

I can't seem to find a full version of the article available online for
free any more, I think I may have the PDF stashed away somewhere though
so if you want to get ahold of it let me know and I'll see if I can dig
it up.

On Feb 17, 6:13 pm, Logan Kearsley <chronosur...@gmail.com> wrote:


> If the planet is geologically active, carbon dioxide
> will build up until it causes the Snowball Earth to melt.

Well, there's your answer: have the planet go snowball after volcanic
activity has ceased. Just have your planet be smaller than Earth, or
have fewer radioisotopes to begin with.


Doug M.

On Feb 18, 1:48 am, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> Logan Kearsley wrote:
> > sigidu...@yahoo.com wrote:
> >> On Feb 17, 11:03 am, Logan Kearsley <chronosur...@gmail.com> wrote:
>
> >>> Thoughts?
> >> This sounds very similar to "Snowball Earth", a theory that involves
> >> super-ice-age conditions in the late Precambrian period.
> > [...]
> >> One other problem is that Snowball Earth would have been a temporary
> >> state, lasting only some tens of millions of years. But that could
> >> probably be handwaved too.
>
> > Similar, but not identical. It needs to be a permanent condition, so
> > there's at least a good billion years with large areas illuminated but
> > in deep freeze. If the planet is geologically active, carbon dioxide
> > will build up until it causes the Snowball Earth to melt. As I said
> > for idea #2, there needs to be some reason why that sort of thing
> > can't happen. I think it can be handwaved for idea #1 by saying that
> > higher CO2 pressure just causes more CO2 to precipitate out on the
> > antistellar cap, but that's not an option for #2.
>
> A while back I read the 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
> (<http://dx.doi.org/10.1006/icar.1997.5793>) and IIRC the simulations
> they used suggested that as soon as the antistellar pole of a
> tide-locked world got cold enough for carbon dioxide to freeze out the
> atmosphere would permanently "collapse" into a frozen state because all
> the greenhouse gas that could potentially warm it back up again would
> get trapped there.

This does not make sense to me. If CO2 were the only component in the
atmosphere, then it makes sense, but if there's anything else around
with a lower freezing point, it will still be possible for the
remaining atmosphere to move heat from the lightside to the darkside.

> There were some interesting speculations about how stable some planetary
> atmospheres might be. For example, M dwarfs often have extreme starspot
> activity, and large persistent starspots can reduce the insolation a
> planet receives by a consider amount over a timescale of months. In some
> cases this could be enough to cause enough CO2 to freeze out on the far
> side of the planet to permanently flip it over into an iceball state. In
> the less extreme case where a planet is merely cold enough for all the
> water to permanently freeze out into an icecap on the antisolar pole,
> the lack of liquid water puts a stop to carbonate sequestration and CO2
> starts building up in the atmosphere until the icecap melts again.

If it's cold enough that CO2 precipitates, it must also be cold enough
for water to permanently freeze out on the darkside (unless glaciers
creep over the terminator and the lightside is still warm enough to
melt them back into a sea), thus stopping sequestration. What I'm
hoping in this case is that dry-ice precipitation would provide a new
sequestration mechanism to keep the CO2 content of the atmosphere
right around the vapor pressure of CO2 at darkside temperatures.

> I can't seem to find a full version of the article available online for
> free any more, I think I may have the PDF stashed away somewhere though
> so if you want to get ahold of it let me know and I'll see if I can dig
> it up.

I've got a copy. It's not quite ideal, because all of the simulations
are of planets with orbital periods on the order of days (being colder
and farther out, I expect my alien world to rotate much more slowly),
and they're looking mainly for situations that would produce a zone of
human-comfortable temperatures, but still a useful reference for
guessing at temperature gradients and whatnot.

-l.

On Feb 18, 7:10 am, sigidu...@yahoo.com wrote:
> On Feb 17, 6:13 pm, Logan Kearsley <chronosur...@gmail.com> wrote:
>
> > If the planet is geologically active, carbon dioxide
> > will build up until it causes the Snowball Earth to melt.
>
> Well, there's your answer: have the planet go snowball after volcanic
> activity has ceased. Just have your planet be smaller than Earth, or
> have fewer radioisotopes to begin with.

Then there needs to be some way to replace the volcanic cycling of
nutrients. Volcanoes don't just release CO2, they get phosphorus and
sulfur and iron and all sorts of other useful trace elements that are
otherwise lost forever in seafloor sludge back to the surface. On a
non-snowball world with oceans, lack of geologic activity means
nutrients eventually all get leached from the surface and stuck in
unproductive seafloor sludge, and everything starves and dies.
I'm not nearly so sure how things would work on a snowball world.

-l.

Logan Kearsley wrote:
> On Feb 18, 1:48 am, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>> A while back I read the 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
>> (<http://dx.doi.org/10.1006/icar.1997.5793>) and IIRC the simulations
>> they used suggested that as soon as the antistellar pole of a
>> tide-locked world got cold enough for carbon dioxide to freeze out the
>> atmosphere would permanently "collapse" into a frozen state because all
>> the greenhouse gas that could potentially warm it back up again would
>> get trapped there.
>
> This does not make sense to me. If CO2 were the only component in the
> atmosphere, then it makes sense, but if there's anything else around
> with a lower freezing point, it will still be possible for the
> remaining atmosphere to move heat from the lightside to the darkside.

If it is cold enough for CO2 to start freezing out on the antistellar
pole, then the atmosphere is already demonstrably not capable of
sufficient heat transport thaw frozen CO2 back there.

The point the paper was making is that once the antistellar pole's
temperature drops that far for whatever reason it's a runaway process.
All of the CO2 freezes out, the planet loses its greenhouse gases, and
barring something weird like a big increase in the remaining
atmosphere's thickness the temperature stays down permanently. In order
to have any CO2 in the atmosphere you need to make sure the planet's
antistellar pole remains above the freezing point of CO2.

On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> Logan Kearsley wrote:
> > On Feb 18, 1:48 am, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> >> A while back I read the 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
> >> (<http://dx.doi.org/10.1006/icar.1997.5793>) and IIRC the simulations
> >> they used suggested that as soon as the antistellar pole of a
> >> tide-locked world got cold enough for carbon dioxide to freeze out the
> >> atmosphere would permanently "collapse" into a frozen state because all
> >> the greenhouse gas that could potentially warm it back up again would
> >> get trapped there.
>
> > This does not make sense to me. If CO2 were the only component in the
> > atmosphere, then it makes sense, but if there's anything else around
> > with a lower freezing point, it will still be possible for the
> > remaining atmosphere to move heat from the lightside to the darkside.
>
> If it is cold enough for CO2 to start freezing out on the antistellar
> pole, then the atmosphere is already demonstrably not capable of
> sufficient heat transport thaw frozen CO2 back there.

It's demonstrably not capable of sufficient heat transport to thaw
frozen CO2 given not-necessarily-permanent current conditions. That
doesn't mean it can't warm up again.

> The point the paper was making is that once the antistellar pole's
> temperature drops that far for whatever reason it's a runaway process.
> All of the CO2 freezes out, the planet loses its greenhouse gases, and
> barring something weird like a big increase in the remaining
> atmosphere's thickness the temperature stays down permanently. In order

Or something not so weird, like sunspot activity decreasing, thus
increasing insolation. Or dust condensing out of the atmosphere- a
particularly large volcanic eruption might temporarily freeze the
planet. And I don't know how stable it would be, but I can imagine a
cyclic situation where an evaporating ice cap could induce planet-wide
dust storms such as are seen on Mars, which then cool the planet and
cause the cap to re-condense, after which the dust settles and it
starts to warm up again.

> to have any CO2 in the atmosphere you need to make sure the planet's
> antistellar pole remains above the freezing point of CO2.

Even if there's a dry ice cap at the antistellar pole, there will
still be CO2 in the atmosphere- just not very much, with the pressure
set by the vapor pressure of CO2 over the ice cap. And other gases can
still remain.

-l.

Logan Kearsley wrote:
> On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>> If it is cold enough for CO2 to start freezing out on the antistellar
>> pole, then the atmosphere is already demonstrably not capable of
>> sufficient heat transport thaw frozen CO2 back there.
>
> It's demonstrably not capable of sufficient heat transport to thaw
> frozen CO2 given not-necessarily-permanent current conditions. That
> doesn't mean it can't warm up again.

No, but with CO2 absent from the atmosphere you'll have to warm it up
again via some mechanism other than greenhouse effect.

>> The point the paper was making is that once the antistellar pole's
>> temperature drops that far for whatever reason it's a runaway process.
>> All of the CO2 freezes out, the planet loses its greenhouse gases, and
>> barring something weird like a big increase in the remaining
>> atmosphere's thickness the temperature stays down permanently. In order
>
> Or something not so weird, like sunspot activity decreasing, thus
> increasing insolation.

As long as the insolation increases again before too much CO2 has
condensed, sure. The paper discussed some timeframes for this sort of thing.

> Or dust condensing out of the atmosphere- a
> particularly large volcanic eruption might temporarily freeze the
> planet. And I don't know how stable it would be, but I can imagine a
> cyclic situation where an evaporating ice cap could induce planet-wide
> dust storms such as are seen on Mars, which then cool the planet and
> cause the cap to re-condense, after which the dust settles and it
> starts to warm up again.

But with the CO2 gone you don't get any of the warming that it might
have been contributing before the freeze. According to
<http://web.uccs.edu/geogenvs/ges100-online/Chapt4.doc> without the
greenhouse effect Earth's average temperature would be -15 C whereas the
current average is 15 C. If Earth was a tide-locked planet balanced
close to the point of having its CO2 freeze out, and something dropped
the temperature enough to trigger it, to recover you'd need to increase
the heating of the planet enough to overcome that 30 degrees C
temperature deficit that you're no longer getting from the greenhouse
effect. If you've got snowball conditions to deal with the albedo will
be boosted, too, making it even harder.

Personally, I think the "CO2 collapse" scenario their models predicted
sounds quite plausible. Reversing it could be an interesting
terraforming scenario, you could perhaps set up orbital mirrors and try
to raise the antistellar point's temperature enough to get the
greenhouse effect going again.

On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> Logan Kearsley wrote:
> > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> >> If it is cold enough for CO2 to start freezing out on the antistellar
> >> pole, then the atmosphere is already demonstrably not capable of
> >> sufficient heat transport thaw frozen CO2 back there.
>
> > It's demonstrably not capable of sufficient heat transport to thaw
> > frozen CO2 given not-necessarily-permanent current conditions. That
> > doesn't mean it can't warm up again.
>
> No, but with CO2 absent from the atmosphere you'll have to warm it up
> again via some mechanism other than greenhouse effect.

Well, obviously.

> > Or dust condensing out of the atmosphere- a
> > particularly large volcanic eruption might temporarily freeze the
> > planet. And I don't know how stable it would be, but I can imagine a
> > cyclic situation where an evaporating ice cap could induce planet-wide
> > dust storms such as are seen on Mars, which then cool the planet and
> > cause the cap to re-condense, after which the dust settles and it
> > starts to warm up again.
>
> But with the CO2 gone you don't get any of the warming that it might
> have been contributing before the freeze. According to
> <http://web.uccs.edu/geogenvs/ges100-online/Chapt4.doc> without the
> greenhouse effect Earth's average temperature would be -15 C whereas the
> current average is 15 C. If Earth was a tide-locked planet balanced
> close to the point of having its CO2 freeze out, and something dropped
> the temperature enough to trigger it, to recover you'd need to increase
> the heating of the planet enough to overcome that 30 degrees C
> temperature deficit that you're no longer getting from the greenhouse
> effect. If you've got snowball conditions to deal with the albedo will
> be boosted, too, making it even harder.
>
> Personally, I think the "CO2 collapse" scenario their models predicted
> sounds quite plausible.

I find it perfectly plausible. I just don't think that it must
*always* be a permanent condition.
For my current purposes, though, I think ensuring that it *is*
permanent may be the best solution for how to get geologic activity
without increasing greenhouse gas content and warming the planet up-
if anything extra that gets spewed out of a volcano just precipitates
out on the darkside, that ought to be just as good as carbonate
sequestration, no?

That works out nicely for the tidelocked planet scenario, but leaves
me wondering about the high-tilt planet scenario. Perhaps that one can
be saved for later.

I wonder, though, what, if anything, it would do to the planet's
geology to have carbon continuously leached out of the mantle and not
replaced by subduction.

> Reversing it could be an interesting
> terraforming scenario, you could perhaps set up orbital mirrors and try
> to raise the antistellar point's temperature enough to get the
> greenhouse effect going again.

That makes for a nice story idea- planet looks like a prime
terraforming prospect if you just set off a few nukes on the ice cap,
and then you discover the psychrophilic natives....

-l.

John Park wrote:

> Dave Farrance (DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk) writes:
>> Logan Kearsley <chronosurfer@gmail.com> 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.

How much it would affect the dark side would depend on the density of the
atmosphere and the composition, but it would act as a convection engine
moving heat to the cooler regions. And moving moisture to the warmer
region.

The reason why such a system would die out would be the gradual loss of
greenhouse gases over a period of many thousands of years, or millions,
depending on their original partial pressure. And matters such as
vulcanism, as has been pointed out, and the original depth of the
atmosphere, and other such details. (I imagine that an Earth=1 depth
atmosphere would give a static cyclone at least up to the stratosphere, and
to cool that down would take several hundred million years at least.)

But just my 0.02c

Wesley Parish
>
> --John Park

On 20 veebr, 09:17, Logan Kearsley <chronosur...@gmail.com> wrote:
> On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>
> > Logan Kearsley wrote:
> > > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> > >> If it is cold enough for CO2 to start freezing out on the antistellar
> > >> pole, then the atmosphere is already demonstrably not capable of
> > >> sufficient heat transport thaw frozen CO2 back there.
>
> > > It's demonstrably not capable of sufficient heat transport to thaw
> > > frozen CO2 given not-necessarily-permanent current conditions. That
> > > doesn't mean it can't warm up again.
>
> > No, but with CO2 absent from the atmosphere you'll have to warm it up
> > again via some mechanism other than greenhouse effect.
>
> Well, obviously.
>

Why? Why not greenhouse gases other than carbon dioxide?

Like methane? Boiling point lower than that of carbon dioxide.

Imagine... over time, methane concentration in atmosphere slowly
increases, the general temperature rises... till the dark side gets
warm enough to evaporate the carbon dioxide. Runaway greenhouse effect
follows - first the carbon dioxide evaporates, then ice seats and
oceans thaw.

(The cycle has a return side, too: once the oceans are open,
photosynthetic production increases. Small quantities of free oxygen
are released into atmosphere and the surface layer of ocean, while
deep ocean remains anoxic and dead organic matter sediments there. The
free oxygen rapidly removes the methane from atmosphere...)
>
>
> > > Or dust condensing out of the atmosphere- a
> > > particularly large volcanic eruption might temporarily freeze the
> > > planet. And I don't know how stable it would be, but I can imagine a
> > > cyclic situation where an evaporating ice cap could induce planet-wide
> > > dust storms such as are seen on Mars, which then cool the planet and
> > > cause the cap to re-condense, after which the dust settles and it
> > > starts to warm up again.
>
> > But with the CO2 gone you don't get any of the warming that it might
> > have been contributing before the freeze. According to
> > <http://web.uccs.edu/geogenvs/ges100-online/Chapt4.doc> without the
> > greenhouse effect Earth's average temperature would be -15 C whereas the
> > current average is 15 C. If Earth was a tide-locked planet balanced
> > close to the point of having its CO2 freeze out, and something dropped
> > the temperature enough to trigger it, to recover you'd need to increase
> > the heating of the planet enough to overcome that 30 degrees C
> > temperature deficit that you're no longer getting from the greenhouse
> > effect. If you've got snowball conditions to deal with the albedo will
> > be boosted, too, making it even harder.
>
> > Personally, I think the "CO2 collapse" scenario their models predicted
> > sounds quite plausible.
>
> I find it perfectly plausible. I just don't think that it must
> *always* be a permanent condition.
> For my current purposes, though, I think ensuring that it *is*
> permanent may be the best solution for how to get geologic activity
> without increasing greenhouse gas content and warming the planet up-
> if anything extra that gets spewed out of a volcano just precipitates
> out on the darkside, that ought to be just as good as carbonate
> sequestration, no?
>
> That works out nicely for the tidelocked planet scenario, but leaves
> me wondering about the high-tilt planet scenario. Perhaps that one can
> be saved for later.
>
> I wonder, though, what, if anything, it would do to the planet's
> geology to have carbon continuously leached out of the mantle and not
> replaced by subduction.
>
> > Reversing it could be an interesting
> > terraforming scenario, you could perhaps set up orbital mirrors and try
> > to raise the antistellar point's temperature enough to get the
> > greenhouse effect going again.
>
> That makes for a nice story idea- planet looks like a prime
> terraforming prospect if you just set off a few nukes on the ice cap,
> and then you discover the psychrophilic natives....
>
> -l.

On Feb 20, 9:27 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
wrote:
> On 20 veebr, 09:17, Logan Kearsley <chronosur...@gmail.com> wrote:
>
>
>
> > On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>
> > > Logan Kearsley wrote:
> > > > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> > > >> If it is cold enough for CO2 to start freezing out on the antistellar
> > > >> pole, then the atmosphere is already demonstrably not capable of
> > > >> sufficient heat transport thaw frozen CO2 back there.
>
> > > > It's demonstrably not capable of sufficient heat transport to thaw
> > > > frozen CO2 given not-necessarily-permanent current conditions. That
> > > > doesn't mean it can't warm up again.
>
> > > No, but with CO2 absent from the atmosphere you'll have to warm it up
> > > again via some mechanism other than greenhouse effect.
>
> > Well, obviously.
>
> Why? Why not greenhouse gases other than carbon dioxide?
>
> Like methane? Boiling point lower than that of carbon dioxide.
>
> Imagine... over time, methane concentration in atmosphere slowly
> increases, the general temperature rises... till the dark side gets
> warm enough to evaporate the carbon dioxide. Runaway greenhouse effect
> follows - first the carbon dioxide evaporates, then ice seats and
> oceans thaw.

Because they're not likely to be very common. If you start out with
lots of methane, the conditions for collapse will be much colder but
you probably won't accumulate very much CO2 (it will tend to be
destroyed in the reducing environment), and if you start out with lots
of CO2, the planet probably doesn't contain much methane (because it
will tend to be destroyed in the oxidizing environment), or suitable
stuff to make methane out of, barring biological activity.

Might be worth thinking about some other possibilities, though. Maybe
nitrous oxide could work in some special cases- if there's a thin
nitrogen atmosphere and high UV flux to break up water ice and let
hydrogen escape, you could eventually accumulate free oxygen which
would combine with the already-present nitrogen.

> (The cycle has a return side, too: once the oceans are open,
> photosynthetic production increases. Small quantities of free oxygen
> are released into atmosphere and the surface layer of ocean, while
> deep ocean remains anoxic and dead organic matter sediments there. The
> free oxygen rapidly removes the methane from atmosphere...)

-l.

On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> John Park wrote:
> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
> >> Logan Kearsley <chronosur...@gmail.com> 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?
And what happens when the planet's rotational period is significantly
longer than 24 hours?

-l.

Logan Kearsley wrote:

> On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
>> John Park wrote:
>> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
>> >> Logan Kearsley <chronosur...@gmail.com> 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.

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 ...

> 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.

Wesley Parish
>
> -l.

On 21 veebr, 00:51, Logan Kearsley <chronosur...@gmail.com> wrote:
> On Feb 20, 9:27 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
>
>
>
> > On 20 veebr, 09:17, Logan Kearsley <chronosur...@gmail.com> wrote:
>
> > > On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>
> > > > Logan Kearsley wrote:
> > > > > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> > > > >> If it is cold enough for CO2 to start freezing out on the antistellar
> > > > >> pole, then the atmosphere is already demonstrably not capable of
> > > > >> sufficient heat transport thaw frozen CO2 back there.
>
> > > > > It's demonstrably not capable of sufficient heat transport to thaw
> > > > > frozen CO2 given not-necessarily-permanent current conditions. That
> > > > > doesn't mean it can't warm up again.
>
> > > > No, but with CO2 absent from the atmosphere you'll have to warm it up
> > > > again via some mechanism other than greenhouse effect.
>
> > > Well, obviously.
>
> > Why? Why not greenhouse gases other than carbon dioxide?
>
> > Like methane? Boiling point lower than that of carbon dioxide.
>
> > Imagine... over time, methane concentration in atmosphere slowly
> > increases, the general temperature rises... till the dark side gets
> > warm enough to evaporate the carbon dioxide. Runaway greenhouse effect
> > follows - first the carbon dioxide evaporates, then ice seats and
> > oceans thaw.
>
> Because they're not likely to be very common. If you start out with
> lots of methane, the conditions for collapse will be much colder but
> you probably won't accumulate very much CO2 (it will tend to be
> destroyed in the reducing environment), and if you start out with lots
> of CO2, the planet probably doesn't contain much methane (because it
> will tend to be destroyed in the oxidizing environment), or suitable
> stuff to make methane out of, barring biological activity.
>
Are carbon dioxide and methane stable when they are together in mildly
reducing conditions?

> Might be worth thinking about some other possibilities, though. Maybe
> nitrous oxide could work in some special cases- if there's a thin
> nitrogen atmosphere and high UV flux to break up water ice and let
> hydrogen escape, you could eventually accumulate free oxygen which
> would combine with the already-present nitrogen.
>
Do you mean NO or N2O?

N2O condenses as easily as CO2.

> > (The cycle has a return side, too: once the oceans are open,
> > photosynthetic production increases. Small quantities of free oxygen
> > are released into atmosphere and the surface layer of ocean, while
> > deep ocean remains anoxic and dead organic matter sediments there. The
> > free oxygen rapidly removes the methane from atmosphere...)
>
> -l.

On Feb 21, 9:27 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
wrote:
> On 21 veebr, 00:51, Logan Kearsley <chronosur...@gmail.com> wrote:
>
> > On Feb 20, 9:27 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > wrote:
>
> > > On 20 veebr, 09:17, Logan Kearsley <chronosur...@gmail.com> wrote:
>
> > > > On Feb 19, 11:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
>
> > > > > Logan Kearsley wrote:
> > > > > > On Feb 18, 6:12 pm, Bryan Derksen <bryan.derk...@shaw.ca> wrote:
> > > > > >> If it is cold enough for CO2 to start freezing out on the antistellar
> > > > > >> pole, then the atmosphere is already demonstrably not capable of
> > > > > >> sufficient heat transport thaw frozen CO2 back there.
>
> > > > > > It's demonstrably not capable of sufficient heat transport to thaw
> > > > > > frozen CO2 given not-necessarily-permanent current conditions. That
> > > > > > doesn't mean it can't warm up again.
>
> > > > > No, but with CO2 absent from the atmosphere you'll have to warm it up
> > > > > again via some mechanism other than greenhouse effect.
>
> > > > Well, obviously.
>
> > > Why? Why not greenhouse gases other than carbon dioxide?
>
> > > Like methane? Boiling point lower than that of carbon dioxide.
>
> > > Imagine... over time, methane concentration in atmosphere slowly
> > > increases, the general temperature rises... till the dark side gets
> > > warm enough to evaporate the carbon dioxide. Runaway greenhouse effect
> > > follows - first the carbon dioxide evaporates, then ice seats and
> > > oceans thaw.
>
> > Because they're not likely to be very common. If you start out with
> > lots of methane, the conditions for collapse will be much colder but
> > you probably won't accumulate very much CO2 (it will tend to be
> > destroyed in the reducing environment), and if you start out with lots
> > of CO2, the planet probably doesn't contain much methane (because it
> > will tend to be destroyed in the oxidizing environment), or suitable
> > stuff to make methane out of, barring biological activity.
>
> Are carbon dioxide and methane stable when they are together in mildly
> reducing conditions?

Don't know. Possibly, but someone more knowledgeable is free to
correct me on that.

> > Might be worth thinking about some other possibilities, though. Maybe
> > nitrous oxide could work in some special cases- if there's a thin
> > nitrogen atmosphere and high UV flux to break up water ice and let
> > hydrogen escape, you could eventually accumulate free oxygen which
> > would combine with the already-present nitrogen.
>
> Do you mean NO or N2O?
>
> N2O condenses as easily as CO2.

True. Ought to have checked up on that. And NO2 seems to condense even
easier still.
I suppose I actually mean NO, then. Which probably means that the
total atmospheric pressure would continue to drop precipitously as
N2O, NO2, etc. get removed, unless enough NO can be built up to
reverse the process before the nitrogen runs out.

> > > (The cycle has a return side, too: once the oceans are open,
> > > photosynthetic production increases. Small quantities of free oxygen
> > > are released into atmosphere and the surface layer of ocean, while
> > > deep ocean remains anoxic and dead organic matter sediments there. The
> > > free oxygen rapidly removes the methane from atmosphere...)
>
> > -l.

On Feb 21, 4:22 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> Logan Kearsley wrote:
> > On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> >> John Park wrote:
> >> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
> >> >> Logan Kearsley <chronosur...@gmail.com> 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.

Logan Kearsley (chronosurfer@gmail.com) writes:
> On Feb 21, 9:27 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
[...]
>> Do you mean NO or N2O?
>>
>> N2O condenses as easily as CO2.
>
> True. Ought to have checked up on that. And NO2 seems to condense even
> easier still.
> I suppose I actually mean NO, then. Which probably means that the
> total atmospheric pressure would continue to drop precipitously as
> N2O, NO2, etc. get removed, unless enough NO can be built up to
> reverse the process before the nitrogen runs out.
>[...]

Note in passing: I'm not sure about the temperature/ pressure/ composition
conditions you're considering, but at room temp & pressure on Earth,
NO in significant concentrations is immediately oxidised to NO2 (or, more
accurately, the equilibrium is well towards NO2). I suspect if there was
enough oxygen around to start forming NO, you'd also start losing it as NO2.

--John Park

Logan Kearsley wrote:

> On Feb 21, 4:22 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
>> Logan Kearsley wrote:
>> > On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
>> >> John Park wrote:
>> >> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
>> >> >> Logan Kearsley <chronosur...@gmail.com> 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.

On 22 veebr, 14:45, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> Logan Kearsley wrote:
> > On Feb 21, 4:22 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> >> Logan Kearsley wrote:
> >> > On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
> >> >> John Park wrote:
> >> >> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
> >> >> >> Logan Kearsley <chronosur...@gmail.com> 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.)
>
No. Coriolis Effect on Mars is completely unaffected by the fact that
Deimos is nearly synchronous. Rotating synchronously with orbital
movement of a more massive body would produce precisely the same
Coriolis Effect.

> > 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.
>
Earth-standard life handles several months of no Sun at all yearly -
in polar areas (mostly Arctic).

How would a planet look like with planetwide seasons due to
eccentricity rather than seasons opposing on opposite hemispheres due
to inclination as on Earth?

On 2008-02-22, Tux Wonder-Dog <wes.parish@paradise.net.nz> wrote:
> (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.)

Coriolis effect is purely an artifact of a rotating coordinate system.
In particular, it depends upon the *sidereal* day and not solar day.
The confusion is probably not your fault - I've read a few physics
textbooks that either don't make it clear or (occasionally) get it
actually wrong.


> 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.

Even a moderately eccentric orbit won't tide-lock 1:1. If such a
planet were intially in 1:1 resonance, then at perihelion it will be
rotating more slowly than it orbits, and thus tidal drag will act to
speed up the rotation. At aphelion the reverse is true, but the
slowing effect will be very much weaker due to the increased distance.

This is why Mercury is in a 3:2 resonance.


- Tim

Tim Little wrote:

> On 2008-02-22, Tux Wonder-Dog <wes.parish@paradise.net.nz> wrote:
>> (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.)
>
> Coriolis effect is purely an artifact of a rotating coordinate system.
> In particular, it depends upon the *sidereal* day and not solar day.
> The confusion is probably not your fault - I've read a few physics
> textbooks that either don't make it clear or (occasionally) get it
> actually wrong.

Thanks!
>
>
>> 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.
>
> Even a moderately eccentric orbit won't tide-lock 1:1. If such a
> planet were intially in 1:1 resonance, then at perihelion it will be
> rotating more slowly than it orbits, and thus tidal drag will act to
> speed up the rotation. At aphelion the reverse is true, but the
> slowing effect will be very much weaker due to the increased distance.
>
> This is why Mercury is in a 3:2 resonance.

Thanks. That makes sense. Mind you, it does introduce additional
complications into the idea ... a planet in this situation we've been
discussing, with a moderately eccentric orbit and consequently a 3:2
resonance. (Which does raise the question - is it likely that a planet so
close to its star, likely to be 1:1 tidally locked? Dole thought it
likely, but most of the planets in so close that have been observed so far,
have highly eccentric orbits, and the one we've been observing the
longest - Mercury - is in a 3:2 resonance tidal lock. Now there's an M3
planet story or two I've had stashed away for 20 or so years that might
warrant a second look, and a much-needed rewrite ... ;)

Wesley Parish
>
>
> - Tim

On 2008-02-23, Tux Wonder-Dog <wes.parish@paradise.net.nz> wrote:
> Which does raise the question - is it likely that a planet so close
> to its star, likely to be 1:1 tidally locked? Dole thought it
> likely, but most of the planets in so close that have been observed
> so far, have highly eccentric orbits

Well, the ones *very* close in do have highly circular orbits due to
tidal effects. They would not likely qualify as candidate "snowball"
worlds though, even on the cold side.

The rest of the planets we've observed - close or not - have had much
greater eccentricities than in our solar system. Our observations are
very selective, but I don't immediately see why the planets that we
can detect should be much more likely to have eccentric orbits than
those we can't.

There has been some work done on simulating the dynamical evolution of
planetary systems. One study (http://arxiv.org/abs/astro-ph/0703160)
found a very close fit to observed eccentricities of extrasolar
planets without much dependence upon initial conditions or requirement
for arbitrary parameters.

In that respect it seems that our solar system is *very* atypical in
the low eccentricities of its planets.


- Tim

Logan Kearsley wrote:

> On Feb 21, 4:22 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
>> Logan Kearsley wrote:
>> > On Feb 20, 3:39 am, Tux Wonder-Dog <wes.par...@paradise.net.nz> wrote:
>> >> John Park wrote:
>> >> > Dave Farrance (DaveFarra...@OMiTTHiSyahooANDTHiS.co.uk) writes:
>> >> >> Logan Kearsley <chronosur...@gmail.com> 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.

I've read the article. I think I made an error - I had assumed that the
atmospheric circulation would be centred around the hot spot and otherwise
had become static, whereas they had worked on a different assumption -
that atmospheric circulation would be directional as in the Earth's
atmosphere, eg, east-to-west and vice-versa, north-to-south and vice-versa,
and that the hot spot wouldn't override directional circulation.

That said, the atmosphere is divided into two cells based on hemisphere;
that's basic. I didn't see two cyclones, though - it looked like a
simplified version of the Earth's atmosphere.

Wesley Parish
>
<snip>
>
> -l.