Question on red dwarf Earthlike planets

[Junghalli]

I've been doing research on habitable planets of red dwarfs for my own uni lately, and I have some questions on the subject for you knowledgeable people, and maybe some general questions.

1) Just to confirm, I am correct in thinking a lack of a large moon would not be a problem for a tidelocked world, as it would not be subject to serious wobbling of the axis?

2) I was reading a paper that says the minimum greenhouse gas to keep the atmosphere from freezing would be .1 bars partial pressure of CO2, but it also says:

"Maintaining a pCO2 hundreds or thousands of times higher than that on the present Earth on a planet subject to Earth-level insolation could be problematic. However, since the effective grey optical depth
of the present terrestrial atmosphere (containing just 350 ppm CO2 with H2O as the principal greenhouse gas) is approximately 0.9, as against 1.0 for a 1000 mb pure CO2 atmosphere, we can use the latter as a useful approximation (for an Earth-type atmosphere temperatures would be just a few degrees lower over the lit hemisphere), and need not postulate or explain a pCO2 higher than that on the present day Earth."

http://www.as.utexas.edu/astronomy/educ ... /heath.pdf

Should I take this to mean that a tidelocked world of a red dwarf could have a stable atmosphere with a similar composition to ours? I like this idea, as it means the atmosphere would be breathable to baseline humans (more than .02 bars ppCO2 is toxic IIRC). But it also occurs to me, water falls out of the atmosphere at a much lower temperature than CO2, so would water really work as the primary greenhouse gas? Wouldn't the air over the frigid nightside be very dry?

I'm pretty sure Antarctica doesn't get anywhere close to freezing point of CO2 during its long night, but Antarctica is much less extreme than a whole half a planet in perpetual night.

The paper says our atmosphere is roughly equivalent to 1000 mb CO2, while I only need it to be equivalent to 100 mb CO2 (the minimum threshold for keeping CO2 from condenscing out on the dark side), and the amount of CO2 could easily be much higher than the present atmosphere while still being tolerable to humans (~2% vs. ~300 ppm). Perhaps this would help.

Could somebody help me figure this out?

3) What would the nightside look like? Would it be mostly freezing cold and glaciers, or might you have some kind of ecosystem over there?

Also, some other tangentially related questions:

4) Am I correct in thinking that a big problem with habitable moons of gas giants is that, forming beyond the snow line, they'd have huge volatile contents and would be very unEarthlike worlds completely covered in deep oceans and very thick atmospheres? Am I correct in thinking that if you wanted an Earthlike moon it would probably have to be a captured sattelite? And how realistically plausible is a captured sattelite? I understand you'd need something to slow it down - like a grazing collision with one of the other gas giant's sattelites, is that right? I'm sure even if it's fairly implausible I could have one or two in the setting, but would it be a common class of worlds or something unusual?

5) How likely is it that an Earthlike planet could capture a large planetessimal (say Luna or Mars sized) early in its history? How likely is it compared to the odds of an event like the collision that formed our moon?

6) Assuming a large collision like the one that formed our moon, how likely is a big moon to actually form? Is it a likely outcome, or something that requires a specific relatively unusual sequence of events?

7) What factors will influence how thick an Earthlike planet's atmosphere will be? Will a planet with a higher volatile content have a thicker atmosphere? Will more geologic activity mean a thicker atmosphere? Will the nitrogen levels vary widely from planet to planet or be similar (I know it's stayed very similar over the Phanerozoic eon while oxygen levels fluctuated wildly)?

[GrandMasterTerwynn]

I've been doing research on habitable planets of red dwarfs for my own uni lately, and I have some questions on the subject for you knowledgeable people, and maybe some general questions.

1) Just to confirm, I am correct in thinking a lack of a large moon would not be a problem for a tidelocked world, as it would not be subject to serious wobbling of the axis?

As far as I know, correct.

2) I was reading a paper that says the minimum greenhouse gas to keep the atmosphere from freezing would be .1 bars partial pressure of CO2, but it also says:

"Maintaining a pCO2 hundreds or thousands of times higher than that on the present Earth on a planet subject to Earth-level insolation could be problematic. However, since the effective grey optical depth
of the present terrestrial atmosphere (containing just 350 ppm CO2 with H2O as the principal greenhouse gas) is approximately 0.9, as against 1.0 for a 1000 mb pure CO2 atmosphere, we can use the latter as a useful approximation (for an Earth-type atmosphere temperatures would be just a few degrees lower over the lit hemisphere), and need not postulate or explain a pCO2 higher than that on the present day Earth."

http://www.as.utexas.edu/astronomy/educ ... /heath.pdf

Should I take this to mean that a tidelocked world of a red dwarf could have a stable atmosphere with a similar composition to ours?

Yes. I believe the latest in atmospheric modeling suggests that a tide-locked planet will still have substantial atmospheric circulation, keeping the atmosphere from condensing out on the far side.

Wouldn't the air over the frigid nightside be very dry?

That's likely. A global ocean should help moderate things though.

The paper says our atmosphere is roughly equivalent to 1000 mb CO2, while I only need it to be equivalent to 100 mb CO2 (the minimum threshold for keeping CO2 from condenscing out on the dark side), and the amount of CO2 could easily be much higher than the present atmosphere while still being tolerable to humans (~2% vs. ~300 ppm). Perhaps this would help.

A thicker atmosphere with more CO2 would indeed be helpful. A thicker atmosphere could set up superrotational winds to assist with the heat transport.

3) What would the nightside look like? Would it be mostly freezing cold and glaciers, or might you have some kind of ecosystem over there?

It'd be pretty cold. And dark. Any extant terrestrial ecosystems will be based around geothermal features. As will most oceanic ecosystems.

[Junghalli]

Yes. I believe the latest in atmospheric modeling suggests that a tide-locked planet will still have substantial atmospheric circulation, keeping the atmosphere from condensing out on the far side.

Even if partial pressure CO2 is <.02 bars in an oxygen-nitrogen-H20 atmosphere instead of .1 bars in a pure CO2 atmosphere?

Also: assuming an atmosphere that can prevent CO2 from condenscing on the night side, what would the night side probably look like in terms of climate? Would it be mostly extremely cold, or would there be significant areas that would be above freezing (though probably still pretty barren due to the lack of a biological energy source like the sun)?

And how would an ocean, either open or covered by sea ice, effect things?

Thanks.

[Junghalli]

Yes. I believe the latest in atmospheric modeling suggests that a tide-locked planet will still have substantial atmospheric circulation, keeping the atmosphere from condensing out on the far side.

Even if partial pressure CO2 is <.02 bars in an oxygen-nitrogen-H20 atmosphere instead of .1 bars in a pure CO2 atmosphere?

Also: assuming an atmosphere that can prevent CO2 from condenscing on the night side, what would the night side probably look like in terms of climate? Would it be mostly extremely cold, or would there be significant areas that would be above freezing (though probably still pretty barren due to the lack of a biological energy source like the sun)? How fast would air lose moisture and heat once it got to the night zone?

And how would an ocean, either open or covered by sea ice, effect things?

Thanks.