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I was under the impression that planets to be life-friendly have to be close to their red dwarf star to a point they'll be tidally locked (one side always light

I was under the impression that planets to be life-friendly have to be close to their red dwarf star to a point they'll be tidally locked (one side always light other night), meaning their atmosphere would freeze on the dark side and planet would end up without an atmostphere.

CWuestefeld 7y ago
This was my first thought, too, when I saw the article. But our thoughts about the effects of tidal lock on the emergence of life is little more than philosophy, having only one datapoint to extrapolate from, at that one not being tidal locked.
- bmurphy1976 7y ago
  I think there are other loopholes. Imagine a Jupiter sized planet that had an Earth like moon. The Jupiter size planet would probably be tidally locked with the star, but the moon could be tidally locked with the planet, not the star. Given that, it would have quite a varied and complicated day/night cycle.
  - quakeguy 7y ago
    Interresting setup you mention there, the earth-like planets d/n cycle would indeed be very irregular i imagine, depending which orbital speed it would have.
wongarsu 7y ago
Atmospheres are useful, but are they a requirement for calling a planet life-friendly? Life on earth first developed in liquid oceans, not in the atmosphere.
- consp 7y ago
  Wouldn't an ocean vaporise somewhat automatically to create an atmosphere of there wasn't one already?
  - __MatrixMan__ 7y ago
    I think so. I don't know of many liquids whose surface tension is strong enough to resist a vacuum. Also, I've never heard anyone propose mercury (the metal) as a particularly good substrate for life.
  - pault 7y ago
    Well, there's the possibility of liquid water under icy moons.
  - wongarsu 7y ago
    Only if it's exposed to vacuum (or an atmosphere). It might be enclosed by ice or other (preferably but not nessesarily transparent) material. Even if the ocean is exposed, we now have the time it takes for 1. the planet to become tidally locked due to tidal forces, 2. the atmosphere to be stripped away, 3. the ocean to evaporate. That might be plenty of time for higher lifeforms to develop.
sushibowl 7y ago
This was indeed the prevailing wisdom for some time. However, more recent research is somewhat more optimistic. Even an atmosphere 10% as dense as that of earth can circulate heat to the dark side efficiently enough, given the right composition. The night side temperature could be within the parameters required to sustain some form of life. Furthermore, tidal locking is dependent on oceans and atmosphere, and can take many billions of years to occur, or even never. Mercury has plenty of time to tidally lock but is in a 3:2 resonance with the sun. There are even other options; for example, moons of gas giants within the habitable zone would be tidally locked to their primary and thus have a day-night cycle.
- jerf 7y ago
  "However, more recent research is somewhat more optimistic." I am deeply skeptical of that "recent research", which AFAIK is "computer models, where we have zero capability to verify the computer models against even a single data point". The incentives to keep kicking the computer model until it provides something publishable, with no countervailing force provided by real data to be explained by the model, are just too strong for me to take that too seriously.
  - abdullahkhalids 7y ago
    Physics models are often checked against other models (which might have had some confirmation) in simple cases, and there are a lot of other sanity checks you can make on them to ensure they are providing reasonable results. Obviously, one shouldn't blindly accept them without experimental confirmation, but one shouldn't also be wildly pessimistic in believing calculations grounded in three centuries worth of validated equations.
    - jerf 7y ago
      Yes, I'm sure the simulations don't have results like making these atmospheres suddenly collapse into black holes due to errors in the simulation or something. They'd notice. But these atmospheres have to stable across cosmological scales in a highly iterative, chaotic environment. There is a mathematical lower bound on the rate such simulations must leak bits as a result of those things. I don't think we have enough bits of real information to make up for that, as it would take rather a lot. Against the mathematical argument, I set the human argument that, like I said, there's all sorts of incentives to report the one simulation that produced the result that there may be an atmosphere and maybe it could even sustain life! That's a lot of high-profile articles and probably a promotion for getting my department some public attention. Even if hundreds of other simulations all result in "Yeah, the atmosphere freezes out". Between the math saying we can't really expect this sort of simulation to contain meaningful information and the human factors involved, I can't put a lot of confidence in a model which can't be validated against real data. I do find it amazing how people who probably think they're really in favor of science and support it will jump up to defend a methodology that literally runs off of zero data. Can someone explain the scientific process to me clearly that involves having no data at any point?
yellowflash 7y ago
I always visualized that the tidal locking to be sort of like meshed gears, such that the one revolution around itself is same as a rotation around the star/planet if its a satellite. But that shouldn't affect the day/night in this case right? Since we are talking about planets not satellites of planets and they are light sources not just reflecting light from the star. Can you please correct where I am wrong?
- kybernetikos 7y ago
  It follows from "one revolution around itself is same as a rotation around the star" that a planet tidally locked to its star presents the same face to the star at all times, so you have a 'Day' side and a 'Night' side. Neither side of which is likely to be particularly life friendly. Perhaps there might be some 'twilight zone' that could be though...
- __MatrixMan__ 7y ago
  Tidal locking means that the denser side of the lighter body always faces the heavier body, and the less-dense side of the lighter body already faces away from the heavier one. The moon is tidally locked to the Earth, which is why it has a dark side.
  - pault 7y ago
    So the Apollo "earthrise" photos are just "earth"?
    - archgoon 7y ago
      No; they weren't taken from the moon; they were taken from the Apollo 8 spacecraft, which was orbiting, so the Earth did in fact 'rise'.
    - quakeguy 7y ago
      Yes, Earth does not move significantly on the moon sky, if i remember right. It does rotate though. Edit: Archgoon is right, the photos were taken from the orbiting module, so a rise happened.
titzer 7y ago
Such planets might also have moons.
- bencollier49 7y ago
  Not ones with 1.1g!
  - titzer 7y ago
    Why not?
    - Evidlo 7y ago
      Because then it would be a double planet.
      - titzer 7y ago
        It depends on how big the "main" planet is, I guess. But I think we are running into definitional issues here, and it gets technical very fast. First, IAU does not recognize the term "double planet". Second, a body which is large enough to reach hydrostatic equilibrium (i.e. a sphere) but has not yet cleared its orbit is technically not a planet. So I don't know where this leaves us. A Jupiter-sized planet with an Earth-sized satellite would be such a huge mass and volume difference (an even bigger difference than the Earth and Moon) that it seems to odd to term that a "double planet".
        bencollier49 7y ago
        TFA said the planets were rocky and 1.1g.
raxxorrax 7y ago
They could have a resonance orbit that would enable a (slow) day-night cycle. But some theories also suggest that M-class stars tend to flare for the regular radiation diet. Otherwise it would be awesome to have an M-class sun, since they can have lifespans multiple times longer than the current age of the universe.
skribbj 7y ago
I'm sorry, I'm not at all educated in this subject and I might be misunderstanding what you are saying, but isn't Earth the perfect example to argue against this? We're a life-friendly planet that isn't tidally locked?
- bencollier49 7y ago
  I think this is just for red dwarf stars, not ones like sol.
- jbattle 7y ago
  It has to do with the class of star. This star is so cool that the only way for the planet to be warm enough to support life is for the planet to be really close to the star. I don't really understand tidal locking but I think it happens vastly faster at closer orbits - because there is a stronger gravitational gradiant closer to the parent body.
  - XorNot 7y ago
    Tidal lock is caused by differential gravitational attraction. The half of the Earth currently facing the sun experiences more force pulling it towards the sun then the part facing away - which manifests as the spin of the planet having to do work against gravity to keep the spin going. As a planet gets closer and closer to it's star, this gets more and more pronounced and all the various deformations and instabilities begin to favor braking the planet rather then it continuing to spin.

CWuestefeld 7y ago

This was my first thought, too, when I saw the article. But our thoughts about the effects of tidal lock on the emergence of life is little more than philosophy, having only one datapoint to extrapolate from, at that one not being tidal locked.

bmurphy1976 7y ago
I think there are other loopholes. Imagine a Jupiter sized planet that had an Earth like moon. The Jupiter size planet would probably be tidally locked with the star, but the moon could be tidally locked with the planet, not the star. Given that, it would have quite a varied and complicated day/night cycle.
- quakeguy 7y ago
  Interresting setup you mention there, the earth-like planets d/n cycle would indeed be very irregular i imagine, depending which orbital speed it would have.

wongarsu 7y ago

Atmospheres are useful, but are they a requirement for calling a planet life-friendly? Life on earth first developed in liquid oceans, not in the atmosphere.

consp 7y ago
Wouldn't an ocean vaporise somewhat automatically to create an atmosphere of there wasn't one already?
- __MatrixMan__ 7y ago
  I think so. I don't know of many liquids whose surface tension is strong enough to resist a vacuum. Also, I've never heard anyone propose mercury (the metal) as a particularly good substrate for life.
- pault 7y ago
  Well, there's the possibility of liquid water under icy moons.
- wongarsu 7y ago
  Only if it's exposed to vacuum (or an atmosphere). It might be enclosed by ice or other (preferably but not nessesarily transparent) material. Even if the ocean is exposed, we now have the time it takes for 1. the planet to become tidally locked due to tidal forces, 2. the atmosphere to be stripped away, 3. the ocean to evaporate. That might be plenty of time for higher lifeforms to develop.

sushibowl 7y ago

This was indeed the prevailing wisdom for some time. However, more recent research is somewhat more optimistic. Even an atmosphere 10% as dense as that of earth can circulate heat to the dark side efficiently enough, given the right composition. The night side temperature could be within the parameters required to sustain some form of life. Furthermore, tidal locking is dependent on oceans and atmosphere, and can take many billions of years to occur, or even never. Mercury has plenty of time to tidally lock but is in a 3:2 resonance with the sun. There are even other options; for example, moons of gas giants within the habitable zone would be tidally locked to their primary and thus have a day-night cycle.

jerf 7y ago
"However, more recent research is somewhat more optimistic." I am deeply skeptical of that "recent research", which AFAIK is "computer models, where we have zero capability to verify the computer models against even a single data point". The incentives to keep kicking the computer model until it provides something publishable, with no countervailing force provided by real data to be explained by the model, are just too strong for me to take that too seriously.
- abdullahkhalids 7y ago
  Physics models are often checked against other models (which might have had some confirmation) in simple cases, and there are a lot of other sanity checks you can make on them to ensure they are providing reasonable results. Obviously, one shouldn't blindly accept them without experimental confirmation, but one shouldn't also be wildly pessimistic in believing calculations grounded in three centuries worth of validated equations.
  - jerf 7y ago
    Yes, I'm sure the simulations don't have results like making these atmospheres suddenly collapse into black holes due to errors in the simulation or something. They'd notice. But these atmospheres have to stable across cosmological scales in a highly iterative, chaotic environment. There is a mathematical lower bound on the rate such simulations must leak bits as a result of those things. I don't think we have enough bits of real information to make up for that, as it would take rather a lot. Against the mathematical argument, I set the human argument that, like I said, there's all sorts of incentives to report the one simulation that produced the result that there may be an atmosphere and maybe it could even sustain life! That's a lot of high-profile articles and probably a promotion for getting my department some public attention. Even if hundreds of other simulations all result in "Yeah, the atmosphere freezes out". Between the math saying we can't really expect this sort of simulation to contain meaningful information and the human factors involved, I can't put a lot of confidence in a model which can't be validated against real data. I do find it amazing how people who probably think they're really in favor of science and support it will jump up to defend a methodology that literally runs off of zero data. Can someone explain the scientific process to me clearly that involves having no data at any point?

yellowflash 7y ago

I always visualized that the tidal locking to be sort of like meshed gears, such that the one revolution around itself is same as a rotation around the star/planet if its a satellite. But that shouldn't affect the day/night in this case right? Since we are talking about planets not satellites of planets and they are light sources not just reflecting light from the star. Can you please correct where I am wrong?

kybernetikos 7y ago
It follows from "one revolution around itself is same as a rotation around the star" that a planet tidally locked to its star presents the same face to the star at all times, so you have a 'Day' side and a 'Night' side. Neither side of which is likely to be particularly life friendly. Perhaps there might be some 'twilight zone' that could be though...
__MatrixMan__ 7y ago
Tidal locking means that the denser side of the lighter body always faces the heavier body, and the less-dense side of the lighter body already faces away from the heavier one. The moon is tidally locked to the Earth, which is why it has a dark side.
- pault 7y ago
  So the Apollo "earthrise" photos are just "earth"?
  - archgoon 7y ago
    No; they weren't taken from the moon; they were taken from the Apollo 8 spacecraft, which was orbiting, so the Earth did in fact 'rise'.
  - quakeguy 7y ago
    Yes, Earth does not move significantly on the moon sky, if i remember right. It does rotate though. Edit: Archgoon is right, the photos were taken from the orbiting module, so a rise happened.

titzer 7y ago

Such planets might also have moons.

bencollier49 7y ago
Not ones with 1.1g!
- titzer 7y ago
  Why not?
  - Evidlo 7y ago
    Because then it would be a double planet.
    - titzer 7y ago
      It depends on how big the "main" planet is, I guess. But I think we are running into definitional issues here, and it gets technical very fast. First, IAU does not recognize the term "double planet". Second, a body which is large enough to reach hydrostatic equilibrium (i.e. a sphere) but has not yet cleared its orbit is technically not a planet. So I don't know where this leaves us. A Jupiter-sized planet with an Earth-sized satellite would be such a huge mass and volume difference (an even bigger difference than the Earth and Moon) that it seems to odd to term that a "double planet".
      - bencollier49 7y ago
        TFA said the planets were rocky and 1.1g.

raxxorrax 7y ago

They could have a resonance orbit that would enable a (slow) day-night cycle. But some theories also suggest that M-class stars tend to flare for the regular radiation diet. Otherwise it would be awesome to have an M-class sun, since they can have lifespans multiple times longer than the current age of the universe.

skribbj 7y ago

I'm sorry, I'm not at all educated in this subject and I might be misunderstanding what you are saying, but isn't Earth the perfect example to argue against this? We're a life-friendly planet that isn't tidally locked?

bencollier49 7y ago
I think this is just for red dwarf stars, not ones like sol.
jbattle 7y ago
It has to do with the class of star. This star is so cool that the only way for the planet to be warm enough to support life is for the planet to be really close to the star. I don't really understand tidal locking but I think it happens vastly faster at closer orbits - because there is a stronger gravitational gradiant closer to the parent body.
- XorNot 7y ago
  Tidal lock is caused by differential gravitational attraction. The half of the Earth currently facing the sun experiences more force pulling it towards the sun then the part facing away - which manifests as the spin of the planet having to do work against gravity to keep the spin going. As a planet gets closer and closer to it's star, this gets more and more pronounced and all the various deformations and instabilities begin to favor braking the planet rather then it continuing to spin.