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Of course, #askNasa didn't win me a question, but could any astrobiologists comment on this question: Tidal locking means the planets would always have a side f

Of course, #askNasa didn't win me a question, but could any astrobiologists comment on this question: Tidal locking means the planets would always have a side facing the star, leading to very different thermodynamics in terms of climate and weather on the planet, not to mention radiation. Doesn't that very much hurt the chances for life on those planets?

Normal_gaussian 10y ago
I would be very interested in seeing comparative weather simulations for a fictional tidal locked planet to Earth and the other Sol planets.
John23832 10y ago
I'm not an astro-biologist, but I assume that it wouldn't be conducive to life as we know it, but that doesn't rule out all life.
SamBam 10y ago
I don't see why. If anything, life might be even easier if you're constantly getting energy from above, rather than intermittently. In any case, "different climate and weather" doesn't seem to me to imply "hurt the chances for life." If they're in the habitable zone, then they're getting similar radiation as an organism at the far north latitudes of Earth are getting during the summer. I don't know if it makes that much difference to a short-lived bacteria whether it's full sunlight for several weeks at a time, vs full sunlight forever.
fauria 10y ago
I remember reading about 55 Cancri e (1), another tidally locked planet (2) featured in NASA's Galaxy of Horrors as "The Twilight Zone" (3), where life in the boundary seems unlikely. 1. https://exoplanets.nasa.gov/custom_planets/2 https://exoplanets.nasa.gov/custom_planets/2 2. https://exoplanets.nasa.gov/resources/149 https://exoplanets.nasa.gov/resources/149 3. https://exoplanets.nasa.gov/alien-worlds/galaxy-of-horrors https://exoplanets.nasa.gov/alien-worlds/galaxy-of-horrors
jerf 10y ago
The debate rages. The problem is that one side of the planet is essentially exposed to space and thus tends to be at cosmic background temperature, and the other side exposed to the star. It is thought by a lot of people that anything volatile enough to be a gas, ever (so, including water), would rapidly end up migrating over to the frozen side, so even if the planet started with the right mix of water and whatever other volatiles are needed it would shortly not have any in the temperate range. Some have objected that the planet could wobble and periodically unfreeze some of that stuff, and maybe life could exist in a resulting narrow temperate zone. My personal feeling is that it would still far-too-rapidly simply freeze out again, this time out of reach of the wobble, so the parched zone would simply grow to include everything ever touched by the sun rather than forming a stable temperate zone. But we won't really know until we go look at a planet like this, because we don't have one locally to look at. (Plenty of tidally-locked bodies, plenty of bodies with volatiles and enough energy to keep them moving, I'm pretty sure nothing in the Solar system with both.)
- Retric 10y ago
  Oceans can move a lot of heat around a planet, so the cold side could stay well above freezing. Remember it's T^4 so cold areas radiate far less heat. That said, if there where minimal atmosphere then the effects your talking about become a larger issue. Atmosphere is largely a function of solar wind and volcanic activity which relates to the isotopes in a planets core making this hard to predict.
- CWuestefeld 10y ago
  But the planets are close enough to interact gravitationally. Perhaps that would accomplish more than just a slight wobble.
- nabla9 10y ago
  If water freezes on the dark side, moisture in the atmosphere would probably move from warm to dark side and fall down permanently as a snow gradually removing liquid water. If the oxygen and nitrogen freezes and snows down in the dark side (-220 C or so), the warm side can't have atmosphere either. Unless there is some way tidally locked planet can have stable air or sea convection between the sides. I don't think they have.
cstejerean 10y ago
Apparently what would hurt the chance of life in a tidally locked planet the most is that due to being tidally locked the planet would have a reduced magnetic field to protect the atmosphere, and therefore there is a good chance that the planet would lose it's atmosphere over time. https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems#Variability https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_syst...
- cgriswald 10y ago
  Agreed, but there are other variables involved, including strength of stellar wind, density of atmosphere, whether a magnetic field is induced by the stellar wind, the mass of the planet (strength of its gravity), etc.
- kbenson 10y ago
  Does atmosphere include the ocean? Because life developed in the oceans first here, and some has never left.
  - cstejerean 10y ago
    Without an atmosphere you can't maintain a surface ocean, because liquid water can't exist in a vacuum. It's possible for the ocean to exist under a crust of ice though. See Europa for an example. So it's still theoretically possible for life to exist in a subsurface ocean, but I think it's a lot less likely compared to a planet with an atmosphere and temperatures that would support liquid water on the surface.
    - kbenson 10y ago
      > It's possible for the ocean to exist under a crust of ice though. See Europa for an example. That's exactly what I was thinking of. :) > I think it's a lot less likely compared to a planet with an atmosphere and temperatures that would support liquid water on the surface. Sure, but we have little information on how common life is. We're not even sure there's no life on Europa. If Europa supports life, it may be that (basic) life is somewhat common given certain criteria, and while I agree it's probably more common on planets with atmosphere and your statements were not incorrect, it may be that life is actually fairly likely on a planet like that (which is what I, possibly incorrectly, interpreted your statement as ultimately trying to convey).
gydfi 10y ago
Maybe but I like to think there are creatures living in the temperate rim of a tidally locked planet somewhere debating whether life could possibly evolve on a rotating planet. "I mean, there'd be temperature fluctuations of tens of degrees every day! It would be dark half the time! How could life survive in such an unstable environment?"
- gwern 10y ago
  And don't forget: there will be long-term cyclical trends of dozens of degrees due to geometric properties of the orbit and hypothesized tilts!
rybosome 10y ago
I'm not a biologist, but here's a fascinating article on the subject: http://m.nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets http://m.nautil.us/blog/forget-earth_likewell-first-find-ali... TL;DR is that there may exist a band around the planet where the two zones meet that is habitable. I think it's a reasonable supposition that most of the rest of the planet would be uninhabitable.

Normal_gaussian 10y ago

I would be very interested in seeing comparative weather simulations for a fictional tidal locked planet to Earth and the other Sol planets.

John23832 10y ago

I'm not an astro-biologist, but I assume that it wouldn't be conducive to life as we know it, but that doesn't rule out all life.

SamBam 10y ago

I don't see why. If anything, life might be even easier if you're constantly getting energy from above, rather than intermittently. In any case, "different climate and weather" doesn't seem to me to imply "hurt the chances for life." If they're in the habitable zone, then they're getting similar radiation as an organism at the far north latitudes of Earth are getting during the summer. I don't know if it makes that much difference to a short-lived bacteria whether it's full sunlight for several weeks at a time, vs full sunlight forever.

fauria 10y ago

I remember reading about 55 Cancri e (1), another tidally locked planet (2) featured in NASA's Galaxy of Horrors as "The Twilight Zone" (3), where life in the boundary seems unlikely. 1. https://exoplanets.nasa.gov/custom_planets/2 https://exoplanets.nasa.gov/custom_planets/2 2. https://exoplanets.nasa.gov/resources/149 https://exoplanets.nasa.gov/resources/149 3. https://exoplanets.nasa.gov/alien-worlds/galaxy-of-horrors https://exoplanets.nasa.gov/alien-worlds/galaxy-of-horrors

jerf 10y ago

The debate rages. The problem is that one side of the planet is essentially exposed to space and thus tends to be at cosmic background temperature, and the other side exposed to the star. It is thought by a lot of people that anything volatile enough to be a gas, ever (so, including water), would rapidly end up migrating over to the frozen side, so even if the planet started with the right mix of water and whatever other volatiles are needed it would shortly not have any in the temperate range. Some have objected that the planet could wobble and periodically unfreeze some of that stuff, and maybe life could exist in a resulting narrow temperate zone. My personal feeling is that it would still far-too-rapidly simply freeze out again, this time out of reach of the wobble, so the parched zone would simply grow to include everything ever touched by the sun rather than forming a stable temperate zone. But we won't really know until we go look at a planet like this, because we don't have one locally to look at. (Plenty of tidally-locked bodies, plenty of bodies with volatiles and enough energy to keep them moving, I'm pretty sure nothing in the Solar system with both.)

Retric 10y ago
Oceans can move a lot of heat around a planet, so the cold side could stay well above freezing. Remember it's T^4 so cold areas radiate far less heat. That said, if there where minimal atmosphere then the effects your talking about become a larger issue. Atmosphere is largely a function of solar wind and volcanic activity which relates to the isotopes in a planets core making this hard to predict.
CWuestefeld 10y ago
But the planets are close enough to interact gravitationally. Perhaps that would accomplish more than just a slight wobble.
nabla9 10y ago
If water freezes on the dark side, moisture in the atmosphere would probably move from warm to dark side and fall down permanently as a snow gradually removing liquid water. If the oxygen and nitrogen freezes and snows down in the dark side (-220 C or so), the warm side can't have atmosphere either. Unless there is some way tidally locked planet can have stable air or sea convection between the sides. I don't think they have.

cstejerean 10y ago

Apparently what would hurt the chance of life in a tidally locked planet the most is that due to being tidally locked the planet would have a reduced magnetic field to protect the atmosphere, and therefore there is a good chance that the planet would lose it's atmosphere over time. https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems#Variability https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_syst...

cgriswald 10y ago
Agreed, but there are other variables involved, including strength of stellar wind, density of atmosphere, whether a magnetic field is induced by the stellar wind, the mass of the planet (strength of its gravity), etc.
kbenson 10y ago
Does atmosphere include the ocean? Because life developed in the oceans first here, and some has never left.
- cstejerean 10y ago
  Without an atmosphere you can't maintain a surface ocean, because liquid water can't exist in a vacuum. It's possible for the ocean to exist under a crust of ice though. See Europa for an example. So it's still theoretically possible for life to exist in a subsurface ocean, but I think it's a lot less likely compared to a planet with an atmosphere and temperatures that would support liquid water on the surface.
  - kbenson 10y ago
    > It's possible for the ocean to exist under a crust of ice though. See Europa for an example. That's exactly what I was thinking of. :) > I think it's a lot less likely compared to a planet with an atmosphere and temperatures that would support liquid water on the surface. Sure, but we have little information on how common life is. We're not even sure there's no life on Europa. If Europa supports life, it may be that (basic) life is somewhat common given certain criteria, and while I agree it's probably more common on planets with atmosphere and your statements were not incorrect, it may be that life is actually fairly likely on a planet like that (which is what I, possibly incorrectly, interpreted your statement as ultimately trying to convey).

gydfi 10y ago

Maybe but I like to think there are creatures living in the temperate rim of a tidally locked planet somewhere debating whether life could possibly evolve on a rotating planet. "I mean, there'd be temperature fluctuations of tens of degrees every day! It would be dark half the time! How could life survive in such an unstable environment?"

gwern 10y ago
And don't forget: there will be long-term cyclical trends of dozens of degrees due to geometric properties of the orbit and hypothesized tilts!

rybosome 10y ago

I'm not a biologist, but here's a fascinating article on the subject: http://m.nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets http://m.nautil.us/blog/forget-earth_likewell-first-find-ali... TL;DR is that there may exist a band around the planet where the two zones meet that is habitable. I think it's a reasonable supposition that most of the rest of the planet would be uninhabitable.