Eyeball Earths

Earth-sized planets found in the habitable-zones of low-mass stars are likely to become tidally locked to the star, with one side baked in perpetual sunlight and other trapped in an eternal night. These so-called "Eyeball Earths" turn out to be extremely common and some famous examples include Proxima b and the planets around TRAPPIST-1. Here, we explain why this tidal locking happens and what it means for the potential habitability of these alien worlds.

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[CoolWorldsLab]

Cool Worlders - do you think that Eyeball Earths are habitable? ヅ

[SailorBarsoom]

If the orbit is a bit eccentric, then you have part of the planet where the sun never sets, part of the planet where the sun never rises, and part where the sun rises for a while, changes its mind, and goes back down over the same horizon. This expands that narrow "twilight band" of habitability.

A place like TRAPPIST-1, where there are so many Earth-sized planets so close together, might tidally effect each other enough to stir up iron cores and produce powerful planetary magnetic fields.

[genexu]

even if the iris region of the eyeball earth might have habitable temperature, it must be windy like hell.

[FirefoxisredExplorerisblueGoog]

Would love to see a video about tidal heating. Perhaps one about Neptune and it's moon Triton would be cool too? Since they have a similar relationship with each other as the Earth and the Moon but in the opposite way. Or should I say retrograde way?

[RRW]

What if the planet is in a binary system with one massive star and a red dwarf, with the red dwarf orbiting like a planet around the larger star and the planet acting like a moon? Obviously the day side would be subject to the same heat effects (especially when the stars are aligned), but could the night side potentially get get (and stay) hot enough for life?

[genexu]

Curious how Earth and moon formed such unusual orbits. Could the axial tilt due to the blow that knocked eath tilted by 23°, grazed the earth and formed the moon? It's unnatural to form such a tilted orbit.

[vatsalpanwar]

Could such an eyeball effect also occur on the atmospheres of tidally locked hot Jupiters?

[jonasmuller]

Hey really cool video! Although I didn't quite get why the eyeball-planets would specifically have this huge vortex on them instead of another cloud/weather structure.

A video about tidal heating would be really interesting! Especially concerning the Jovian moons like Io and Europa. And also Saturn's Enceladus.
BTW: You as a professional (Exo-)Moon-ologist:what is your opinion where is life easier and/or more probable to be found, on Europa or Enceladus?

[milky_wayan]

Assuming they don't lose all their volatiles during their formation, or gradually lose them due to solar flares, then they could be interesting vacation spots. Not sure about life. Can eyeball worlds have magnetospheres?

[araptuga]

I'm wondering if there's any new work on this that's worthy of a Cool Worlds update?

Others would be locked, but as noted here, with a wide diversity of results, from water/atmosphere/volatiles blown away by flares, to completely frozen out on dark side, to water but not atmosphere frozen out, to both still able to circulate in some manner, and thus maintain livable conditions for at least the terminator ring zone, and so on.
Also, regarding flares: do all red dwarfs experience them? Do they tend to die out over the course of first several billion years? If the latter, could planets maintain atmospheres for the duration?
Given that these could be incredibly common, has there been any more recent work that would indicate how common these different scenarios would be?

[jamesgeary]

Just watched this. Do you think there's a spectrum of eyeball worlds where different longitudes away from the substellar point might be optimal. For example, ranging from where only the substellar point is habitable to where only the bare terminator or even the night side are cool enough for life?

[garethdean]

1.) Hold on there, a two-hour day; would the Earth be stable at that sort of speed? Wouldn't it start to throw material off of its equator due to centripetal forces?

2.) So our sun isn't average, it's comparatively heavy and bright? Indeed does this make Earth possibly unusual in regards to habitable planets?

[Zarith]

It would be cool to live on a moon tidally locked to a planet tidally locked to a star and still getting a day night cycle through that interaction.

[Qwayeasn]

3:50 Ah, thank you **steps into time machine**

[rJaune]

If the atmosphere condensed on the far side of an Eyeball Earth couldn’t the planet
reorient itself because of the redistribution of mass?

[locust]

Can a tidally locked planet theoretically have a rotation around its terminator axis?

[Cntntne]

Awesome work David! It's great to see active researchers doing this sort of outreach. Have you considered collaborating with popular youtubers like Henry from Minutephysics and Derek from Veritasium in order to gain more followers ans reach a wider audience?

[tuttt]

The moon pulls on the tidal bulge, slowing the Earth. The tidal bulge pulls back on the moon speeding it up and forcing it into a larger orbit.

[THX..]

My opinion is life begins deep inside a planet as a product of geologic activity. It then migrates to the surface as it evolves. If true then any planet of sufficient mass, made of the right elements could spawn life. Though this is point where the outlook for life sours.

To move beyond the most simple forms life must find conditions on the surface that are favorable. This means along with liquid water, carbon dioxide and a host of other gases in the atmosphere the world must have a magnetic field to shield radiation and hold the atmosphere in, be in the habitual zone of it's star, have a reasonably short day night cycle.

Any planet tidally locked to it's star seems to have little chance of producing anything more than bacteria. If it's all ocean or at least covered by a very large ocean maybe sea life, as that the water would shield radiation and moderate temperatures, but even to get this far may not be possible. Trying the evolve life along the day night terminator seems a hopeless affair. Having an endless hurricane battering the day night terminator certainly won't help. Plus no rotation means no magnetic field means no atmosphere.

For higher life forms a planet needs to escape being tidally locked to it's star. This means worlds with a large moon, worlds that are large moons and worlds that are part of binary planets. Of these choices the moons of gas giants are likely the most abundant.

Taking our solar system as example. By current definition there are 8 planets, 4 rocky planets like earth, 4 gas giants. Only 1 of the 4 rocky planets has a large moon whereas all 4 gas giants have large moons. In fact all but 1 have multiple large moons.

[ellell]

Think of tidally locked planet very close to the star with boiling hot day side and condensed water on the night side (instead of freezing out) that is lit by powerful auroras to where plants grow on the night side .. ?? ..?? This idea would expand the habitable zone even much closer to red dwarf stars you think ??