Tidal heating versus extrasolar moon habitability

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Tidal heating versus extrasolar moon habitability

Post by PlutonianEmpire on 25th March 2012, 7:57 pm

I recall last month, a few news articles were published regarding how extreme tidal forces and heating would trigger runaway greenhouses and strip planets of whatever oceans they might have.

One such article: http://www.space.com/14535-alien-planets-water-tidal-forces.html

My question is, what implications does this discovery have for potentially habitable extrasolar moons of giant planets?

I'm guessing that even giant planets, at least those in their sun's habitable zone, might have a "habitable zone" of their own, where if a moon, one that is potentially big enough to become habitable, is too close, tidal heating eliminates the oceans and/or the moon is torn apart due to tidal forces, and yet if the moon is too far, the length of its day (assuming tidal locking) could pose problems of its own?

Another significant factor might the radiation emitted by the host planet.

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Re: Tidal heating versus extrasolar moon habitability

Post by Sirius_Alpha on 25th March 2012, 8:14 pm

The paper just showed up on arXiv. http://arxiv.org/abs/1203.5104

I don't understand how Space.com was so fast on this. Usually they're months behind.

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Re: Tidal heating versus extrasolar moon habitability

Post by tommi59 on 27th March 2012, 2:50 am

I suppose longer day does not matter against being too close.Neverthelles I do not suppose the moon would be so close to host planet to disable habitability on moon
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Re: Tidal heating versus extrasolar moon habitability

Post by Neuron on 3rd April 2012, 2:34 pm

It can also help habitability. Like in a moon orbiting a gas giant that is slightly further from its sun that the standard habitable zone. The "presumed temperature" might be -80 degrees Celsius, yet in actuality it will be well above zero, with liquid water oceans on the surface. Imagine a big Europa with a more Earthlike composition.

Look at Jovian moons. All of them except Io are icy cold. I doubt tidal effects will dessicate exomoons except for the innermost one/ones.

Plus, tidal heating manifests in volcanism. It is not going to magically flash oceans into steam.

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Re: Tidal heating versus extrasolar moon habitability

Post by Planetory on 11th June 2012, 5:14 pm

I agree with Neuron, alarge Europa-like moon around a Hot Jupiter might be even more habitable if it was exposed to larger tidal forces from the host star. However, what if the hot Jupiter it orbits had a fairly eccentric orbit itself? Then, there would be the prospect of seasons on the large moon, which could help or hinder habitability depending on just how eccentric the orbit is.

Also, what if a Venus-like planet did get stripped of some of its atmosphere? Not enough to leave it completely bare, but enough so that atmospheric pressure and surface temperature are decreased to habitable levels. In this case, would atmospheric stripping make the planet more suitable for life?

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Re: Tidal heating versus extrasolar moon habitability

Post by Sirius_Alpha on 11th June 2012, 6:10 pm

Neuron is suggesting a moon of a giant planet that is typically considered too cold for life (farther from the star than the traditional habitable zone) might be kept warm with tides. Hot Jupiters are giant planets that are very close to their star (with orbital periods typically < ~10 days) If you have a moon around a hot Jupiter, it's already too warm, and tidal heating is just going to worsen that. Besides, it is highly unlikely large moons can be stable around hot Jupiters. Tidal effects will cause the moon to fall into the planet.

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Re: Tidal heating versus extrasolar moon habitability

Post by PlutonianEmpire on 11th June 2012, 6:44 pm

Yes, and on top of that, there's an article recently discussing the observation that hot jupiters tend to be the sole planet in their system, implying that said hot jupiters may have ejected other planets from their systems (or, at least kicking them to more distant orbits), or collided with/consumed them, as they migrated to their current observed orbits. Plus, this means that any moons the hot jupiter may have had were probably ejected (or destroyed) as they got close to their star.

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Re: Tidal heating versus extrasolar moon habitability

Post by Planetory on 12th June 2012, 2:05 pm

yes, yes, that of course makes sense. Brain Fart, I was thinking Jupiter-like planet and for some reason kept typing Hot Jupiter instead. Believe it or not, I know what a Hot Jupiter is!

So let's try this again and hope that it assuages the anger from one of the previous posts: I agree with Neuron, a large Europa-like moon around a Jupiter-like planet might be even more habitable if it was exposed to larger tidal forces from the host star. However, what if the Jupiter it orbits had a fairly eccentric orbit itself? Then, there would be the prospect of seasons on the large moon, which could help or hinder habitability depending on just how eccentric the orbit is.

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Re: Tidal heating versus extrasolar moon habitability

Post by Sunchaser on 13th June 2012, 7:44 am

I'll admit I don't know the full story regarding eccentric planets and their moons, but I tried this in a gravity simulator, and the moons didn't stay.
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Re: Tidal heating versus extrasolar moon habitability

Post by Planetory on 13th June 2012, 11:59 am

Interesting. What is the range of eccentricity values you are considering?

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Re: Tidal heating versus extrasolar moon habitability

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