Tidal Heating Shrinks Goldilocks Zone Around Red Dwarfs

scibri writes "An overlooked factor could shrink the habitable zone for planets around M-class dwarf stars by as much as 50%. For these smaller, cooler stars, the habitable zone was thought to extend to relatively close orbits. But as you get closer to a star, the tidal force it exerts on a planet increases. Since planets do not have perfectly circular orbits, tidal forces cause the planet to flex and unflex each time it moves closer to or further from its star; kneading its interior to produce massive quantities of frictional heat — enough to scour the planet of any liquid water. Because M-class dwarf stars are the most numerous in the galaxy, and close-in planets are easier to spot than more distant ones, such stars have been a major target for planet hunters seeking Earth-like worlds. But now it seems we may have been looking in the wrong place for Earth's twin."

Comments

Friction is hell

[smittyoneeach]

Friction is hell
In space or on face
Sudsy blade orbits
Don't leave a trace
Burma Shave

Goldilocks and the Red Dwarfs

[Jeng]

Funny, I don't remember that one.

arguement should cut both ways

[anwyn]

Why does this arguement not show that there are places that should be to cold, but are not because of tidal heating?

Could someone please explain this to me?

Re:arguement should cut both ways

[bored_engineer]

In the context of red dwarfs, it's about distance. Gravity falls off with the square of the distance from the source. So, as the distance increases, the influence of the primary would fall off, thereby reducing the tidal heating. I suppose that it could heat a planet orbiting a brown dwarf, but a brown dwarf would have no (or little) emissions in the visible spectrum. Perhaps something besides terrestrial life could find it habitable, but I don't think we would be able to live there.

Re:arguement should cut both ways

[Lithdren]

I dont see anything that claims thats not possible, so I dont quite get where you get this from. It would be a strange place indeed, a planet warmed by tidal friction from within would have a very different biology of life. I'd imagine most life would be deep underwater near rifts in the oceans floor, there'd be no point in forming near the surface, depending on what caused the tidal forces.

Would make for an interesting long-term strategy for an advanced race to survive past the life of stars, if you can heat from within via tidal forces around say, a super massive black hole. Just dont be the jerk to mess that one up.

"Sir! We forgot to exchange values between Metric and Imperial, the entire planet is about to get sucked into a black hole!"
"Well...alteast we dont need to worry about budget cuts next year."

Re:Moons around large planets as well?

[justin12345]

You're confusing red dwarves with white dwarves. Red dwarves form small, white dwarves are the stellar cores of G type stars after they have blown off most of their mass during their red giant phase.

Tidal heating is self-eliminating

[Immerman]

They compare to Jupiter's moon Io in the article, whose proximity causes tidal heating and makes it the most geologically active body in the solar system. However, all the energy that goes in to tidal heating is drawn from its orbital energy and would normally cause the orbit to circularize (tidal dissipation), thus eliminating the heating - the only reason that doesn't happen with Io is because it's locked in a 1:2:4 orbital resonance with Europa and Ganymede, both of which have much greater orbital energies.

Now I imagine this would take longer with a planetary-sized orbit than with a moon-sized orbit, but unless the planet migrated inwards considerably I would expect that it would have largely occurred while the proto-planetary cloud was still coalescing. It might contribute to a longer cooling period, but I don't see how that's really a problem, it's not like a lot of these dwarf stars aren't considerably older than Sol, even a few billion extra years years of cooling would still give life there a head start on us. In fact, considering that Earths volcanic phase is when life here got it's start, a mechanism that might have extended that period seems like it could make life even more likely.