It's me again with another perplexing article from Astrobio.net .

http://astrobio.net/news/modules.php...rder=0&thold=0

According to this article, plate tectonics are necessary for life, and smaller planets wouldn't have them. And

"The team found that super-Earths would be more geologically active than our planet, experiencing more vigorous plate tectonics due to thinner plates under more stress".

OK, I don't know why plate tectonics would be related to the size of a planet. I thought it had more to do with 1) whether the planet was hot inside, and 2) whether there was another planetary body exerting gravity against it. I believe Jupiter's moon Io is very geologically active because Jupiter's gravity pulls its insides around (which causes it to be hot & have lots of lava, in fact they call it the 'pizza pie planet'.
So one could say that "pizza is what's on Io's Plate." )

I would actually think the Super Earths would be less geologically active, because there is so much more mass in them, thus higher gravity, and if they have a hot core, there would still be so much more material shielding the core from the surface.

Interestingly, the article thinks that Super Earths would be a great vacation spot, with temperate climate & lots of balmy hot springs. Sure, the gravity would be 3X that of Earth, but the author doesn't think that would be such a problem.

I do! I thought you would weigh 3X as much? Who would want that???

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There are already two active threads on this topic:

Earth, Barely Habitable?

Earth on Borderline for Life

Grant Hutchison

Smaller planets would cool down quicker, thus stopping tectonics. Larger planets are likely to be hotter. The added heat from decay and heat of formation will make much more of the planet liquid. This could cause more vulcanism.

Another factor may be liquid water. Venus has no tectonics and should be compositionally similar.

Larger planets will definitely be more active; volume scales up much more rapidly than surface area (by the cube versus the square, respectively IIRC), which is just a roundabout way of saying that more massive "Earths" have more hot mass with less area to cool off with.


In short: just the way a liter of water will cool off much more slowly than a milliliter, so will a more massive terrestrial planet cool more slowly.

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Great chance to do some strength training. It might serve as the 24-hour fitness planet -- where walking is a workout.

Or, go swimming when your joints ache.

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The author likely assumed three times the gravity results from three times the mass. I'll guess 1.5 g unless the average density is more than the 5.5 times water of Earth. 1.5g would give a good workout: 3g would likely kill even very fit humans in a few days. Neil

Very fat people seem to manage with an approximation of 3g. At least they last longer than a few days.

From the link, they're evidently talking about a 10-Earth-mass planet.

Grant Hutchison