Water Planets

Jan 22, 2010
A diagram of the interior section of a water planet, to scale. The model is for a planet that is 5 earth-masses and 50% water. The ice layers are made of various types of water ice. Credit: Fu et al., 2010

Of the roughly 420 extra-solar planets now known, about a dozen are in the newly named category of "super-earths," planets whose masses are in between of two and about fifteen earth-masses.

So far it has not been possible to probe the interior structures of these objects directly, but scientists expect them to be one of three types: gas dominated (like Neptune), or rocky (like Mercury), or rich in (more so than Earth).

Astronomers expect that new satellites designed to detect and characterize will soon be able to provide clues to their interiors, especially from those super-earths whose atmospheres can be sampled because their orbits take them directly in front of and behind their star as seen from earth. To prepare for those results, scientists have begun modeling planetary interiors.

CfA Dimitar Sasselov, together with two of his colleagues, have begun the pioneering task of modeling the interiors of super-earths. They address in particular the class of objects rich in water. They define a "water planet" as any super-earth whose mass is more than 10% water, whose core is made of silicates or metals, and whose is lacking in significant amounts of gas. They model nine possible water planets with a range of masses and water contents (up to 50%), and study the near-surface layer for icy or ocean-like properties.

The astronomers find that the interiors of water planets have relatively well-defined zones, with characteristic densities and other properties that depend on the planets' masses, stellar heating, and other parameters. A water planet made of 50% water, for example, would have several layers thousands of kilometers thick, each of a different form of water-ice, with a thin outer crust made of yet other forms of , and a liquid ocean between crust layers. The results also help define an evolutionary time for the structures, which evolve distinctly over periods from a hundred thousand to a hundred million years. The study provides a realistic new basis for interpreting future observations of water planets.

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User comments : 4

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RayCherry
not rated yet Jan 25, 2010
Is there also a classification for "non-water" liquid planets/moons?
LKD
not rated yet Jan 25, 2010
I am curious. Wouldn't there be a water layer close to the core persistent due to gravitational convection as it seems that all planets start with a molten core? Maybe possibly exaggerated by tidal forces? For example, Enceladus.
Adriab
not rated yet Jan 26, 2010
So, even though it is compressed to an incredibly density, you suggest it could be hot enough to be molten or plastic?

That'd be interesting. I'm not sure if our understanding of the processes at hand is deep enough to be able to figure that out (yet). Perhaps with some computer models?

If it were the case, I think it would behave quite differently than the liquid water we know and love.

I know there is so called "hot-ice" deep in the earth, it is not the nice crystalline structure like our surface ice. It is held in a solid state by that huge pressure and it has quite a high temperature.
LKD
not rated yet Jan 26, 2010
I'll have to look hot ice up, thank you. I imagine in an entire universe it is 'possible', however unlikely, as our own planet's breadth of lifeforms in a terribly inhospitable universe shows.

But you bring up something I keep forgetting, we know far little of the planet we are standing on. We would be well served to study Earth's core and mantles.

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