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

Re:Friction is hell

[xevioso]

You are weird.

Goldilocks and the Red Dwarfs

[Jeng]

Funny, I don't remember that one.

Re:Goldilocks and the Red Dwarfs

[Jeng]

Yea, I was surprised it got modded up, I was amazed someone modded it Interesting.

It does of course make sense that gravitational forces would warm up orbiting bodies, we even have plenty of examples of that happening here in our own solar system.

Time to modify another variable from the Drake Equation.

I blame Arnold J Rimmer

[dkleinsc]

That smeghead makes everything around Red Dwarf uninhabitable.

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:arguement should cut both ways

[amRadioHed]

It does work both ways, where did you get the idea it doesn't? The fact that planets closer to their star may be warmer then expected is more relevant though, since that's where astronomers tend to look for planets.

Re:arguement should cut both ways

[ulzeraj]

This makes me think that most of these planets are tidally locked to their parent star. They are very hot on the side facing the star and cold on the other side.

If you put tidal heating on the formula, maybe those freezing dark sides are not so freezing after all.

Re:arguement should cut both ways

[wierd_w]

What about other small, bright, and dense objects?

A white dwarf, for instance?

You also discount the potential for exotic photosynthetic life around the brown dwarves. For instance, here on earth normal green photosynthetic plants can absorb multiple photons of red freq light and combine the energy from them with some clever quantum mechanics to have enough energy to push a high energy electron into a chemical bond site.

It doesn't seem inconcievable that there could be very slow respiration organisms that have very large "leaves", and which collect near IR photons en mass. If the photon flux overall is high enough, they would gather enough photonic energy from the brown star to make chemical energy sources. (Granted, this would have to be near IR, not true IR, because sufficiently high real IR flux would toast the surface like a heat lamp. Water is also strongly opaque to IR and nIR light, so a water rich atmosphere would scatter it pretty heavily.)

A large world, with a reasonably "bright" brown star emitting lots of red and nIR light, and just enough gravitational tug, and you have the potential for some interesting surface life.

Re:arguement should cut both ways

[K. S. Kyosuke]

Once the tidal heating contribution to the total thermal budget is significant, you can be sure it won't last for long. It wouldn't last the 4,300 My that are the age of Earth, and the 10 Gy that are the lifetime of our Sun. The even longer lifespan of a dimmer star hardly compensates for it. Life needs time to emerge and to evolve, and rather stable conditions as well. We on Earth happen to be fortunate, the hypothetical Reddwarfeans wouldn't be.

Re:arguement should cut both ways

[K. S. Kyosuke]

A white dwarf, for instance?

A white dwarf doesn't last for long and is a relic of a previous red giant that has been thoroughly baking your planet for quite some time. If you look upon the sky and see a white dwarf as your sun, check your pulse, since you're most likely a ghost.

Re:Moons around large planets as well?

[Jeng]

Io would be a good example of that since it is the most geologically active object in the solar system. (thank you wikipedia)

Headline is wrong, looking in the wrong places

[Tekfactory]

In TFA they say that people looking for Exo-planets are looking for ones with close orbits. They believe now that because of tidal forces those planets would have hotter temps and not be candidates for a Earth-like planet.

Looking for close orbit planets is a fine way to find exoplanets.

What they should say is that looking for close orbit planets is not a good way to find earthlike planets with liquid water.

Now take in your head the originally believed habitable zone, you are going to have to shorten that on the side closer to the star. One would not necessarily extend that zone an equal distance away from the star as planets not in close orbits won't get the extra heating.

Re:Idiots!

[Jeng]

It is never explicitly stated that Goldilocks did not associate with Dwarfs.

Teach the Controversy!

Re:Moons around large planets as well?

[Intrepid imaginaut]

I'm a bit hazy on my stellar life cycles, but wouldn't red dwarfs have been larger stars in the past, and have stripped the atmospheres of any planet close enough to be in the habitable zone?

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.

Re:Tidal heating is self-eliminating

[goodmanj]

Also worth pointing out that even if a red dwarf planet's orbit were perturbed by other worlds, as is the case with Io, you won't get strong heating. The distances between a red dwarf's planets will be far larger than the distance between Jupiter's moons, so the orbital perturbations will be much *much* weaker.