Eyeball Earths

An interesting conjecture about tidally locked terrestrial planets around M dwarfs:

http://www.astrobio.net/exclusive/5462/eyeball-earths?buffer_share=8361d&utm_source=buffer&utm_medium=twitter&utm_campaign=Buffer%253A%252BSETIInstituto%252Bon%252Btwitter

Quote :

Alien worlds resembling giant eyeballs might exist around red dwarf stars, and researchers are now proposing experiments to simulate these distant planets and see how capable they are of supporting life.

[...] This scenario of permanent day and permanent light could lead to a striking kind of world — one resembling an eyeball. Its night side would be covered in an icy, frozen shell, while its day side would host a giant ocean of liquid water constantly basking in the warmth of its star.

[...] An eyeball planet is one of several possible scenarios for planets in a red dwarf's habitable zone. "A little bit closer to the star — that is, hotter — they would completely thaw and become waterworlds; a little bit further out in the habitable zone — that is, colder — they would become total iceballs just like Europa, but with a potential for life under the ice crust," Angerhausen said. "These planets — water, eyeball or snowball — will most probably be the first habitable planets we will find and be able to characterize remotely. Thats why it is so important to study them now."
The ocean of an eyeball Earth will likely span a range of temperatures. "It's probably pretty hot in the center of the eye and then gradually gets colder towards the edge of the ice crust," Angerhausen said. Still, much remains uncertain — for instance, if the ocean transports heat well, the planet might warm enough all over to turn into a waterworld without ice, he suggested.

[...] Upcoming and current telescopes such as the James Webb Space Telescope might be able to see if planets have eyeball structures. When telescopes improve further, astronomers could look for molecular signs of life on eyeball Earths.

The first image of an habitable planet will be something like this?

It doesn' t take into account the very likely spin-orbit resonances, so lots of that planets could have light and dark periods all over the surface, like our moon or Mercury. Very different of what they have proposed.

And it' s very likely that planetary systems could have some influence on each other (librations?). Multiple planet systems are more frequent than lonely planets in that kind of stars.

pochimax wrote:

It doesn' t take into account the very likely spin-orbit resonances

Did you even read anything about this? Studying the spin-orbit resonance and tidal lock and its effect on habitability is the whole point of this.

I meant that this eyeball planets (or tidally locking ones) will be far less common than planets with spin-orbit resonances or with some kind of librations or chaotic behaviour.

These kinds of planets are defined by having a 1:1 spin-orbit resonance.

Sirius_Alpha wrote:

These kinds of planets are defined by having a 1:1 spin-orbit resonance.

yes, you' re right.

I was talking about 2:3 and other similar spin-orbit resonances. I think 1:1 will be less frequent, around M dwarfs, but it's only an opinion.

Why do you think 1:1 will be rare? It is the most common spin-orbit resonance in the solar system.

(That's not to say there won't be some librations going on, but that shouldn't have too much effect on the eyeball model)

One thing I was wondering about such planets; when it comes to eyeball earths having eccentricities high enough to notice, but still maintain 1:1 spin-orbit, would life, especially when closer to the equator and near the terminator, develop some sort of synchronizing rhythm to the constant back and forth motions of their sun?

Lazarus wrote:

Why do you think 1:1 will be rare? It is the most common spin-orbit resonance in the solar system.

(That's not to say there won't be some librations going on, but that shouldn't have too much effect on the eyeball model)

Because the M dwarf planetary systems will have a lesser mass ratio (planets against its mother star) than the typical gas giant - moon system' s ratio of our' s.

So it' s very likely that, with this mass ratio, planets will not end tidally locked. At least not in planetary systems with earth masses or above.

It actuall turns out that the mass ratios between the giant planets and their moons is actually quite comparable than the observed mass ratios between the planetary systems we see.

That being said, I don't know why a different mass ratio would result in preferences for spin-orbit resonances other than 1:1. Since tidal circularisation tends to drive e to zero, a 1:1 spin-orbit resonance would seem to be the default resting state for most systems.

Especially at the habitable zone of an M dwarf, where the tidal circularisation timescale is far shorter. In a circular orbit, a 1:1 spin-orbit resonance would be the default final state, IIRC.

So, I' m wrong!!