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.

Explore further: Quest for extraterrestrial life not over, experts say

Related Stories

Superior Super Earths

Nov 30, 2009

Super Earths are named for their size, but these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life. They could also provide an answer to ...

Scientists discover a nearly Earth-sized planet (Update)

Apr 21, 2009

(PhysOrg.com) -- Exoplanet researcher Michel Mayor announces the discovery of the lightest exoplanet found so far. The planet, "e," in the system Gliese 581, is only about twice the mass of our Earth. The ...

Earth-like planets may be found soon

Mar 24, 2008

U.S. experts say known planets outside of Earth's solar system, currently numbered at 277, could soon include smaller planets that are closer to Earth's size.

Trio of Neptunes and their belt

May 17, 2006

Using the ultra-precise HARPS spectrograph on ESO's 3.6-m telescope at La Silla (Chile), a team of European astronomers have discovered that a nearby star is host to three Neptune-mass planets. The innermost ...

Researcher simluate characteristics of planetary cores

Feb 20, 2006

University of Minnesota researchers Renata Wentzcovitch and Koichiro Umemoto and Philip B. Allen of Stony Brook University have modeled the properties of rocks at the temperatures and pressures likely to exist at the cores ...

Researcher simluate characteristics of planetary cores

Feb 22, 2006

University of Minnesota researchers Renata Wentzcovitch and Koichiro Umemoto and Philip B. Allen of Stony Brook University have modeled the properties of rocks at the temperatures and pressures likely to exist ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

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.

More news stories

Easter morning delivery for space station

Space station astronauts got a special Easter treat: a cargo ship full of supplies. The shipment arrived Sunday morning via the SpaceX company's Dragon cargo capsule.

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.

Low tolerance for pain? The reason may be in your genes

Researchers may have identified key genes linked to why some people have a higher tolerance for pain than others, according to a study released today that will be presented at the American Academy of Neurology's 66th Annual ...

How to keep your fitness goals on track

(HealthDay)—The New Year's resolutions many made to get fit have stalled by now. And one expert thinks that's because many people set their goals too high.