At the Core

[james_davis_nicoll]

Hydrogen‐helium mixtures at conditions of Jupiter’s interior are studied with first‐principles computer simulations. The resulting equation of state (EOS) implies that Jupiter possesses a central core of 14–18 Earth masses of heavier elements, a result that supports core accretion as the standard model for the formation of hydrogen‐rich giant planets.

Nicked from the Planetary Society Blog

Comments

[le-trombone.livejournal.com]

Nice.

Does this put a stake in the heart of the (some) gas giants don't have a surface theory? Or was that theory already dead and I hadn't noticed?

[(Anonymous)]

This has nothing to do with that. Gas giants certainly don't have any recogisable surface in any familiar sense.

The standard model of gas giant (Jupiter and Saturn) interior has four layers: a relatively thin (hudreds of kilometres) atmosphere of gaseous hydrogen; an outer mantle of liquid hydrogen; an inner mantle of metallic hydrogen (also liquid); and a very small (compared to the rest of the planet) solid core of heavier elements (a mixture of ice, rock, and metal). There isn't a clear transition between the gas and liquid hydrogen layers; it just gradually becomes denser until it behaves more like a liquid than a gas. The nonmetallic-liquid to metallic transition would be a bit clearer, but very deep inside the planet, while the metallic-H2-to-solid-core transition is way down near the centre. This paper doesn't challenge any of that, it's just concerned with the details.

The model has been tested by comparing the orbits of space probes (Galileo and Cassini) to the gravitational field that would be expected from various models of the interior; the standard model is strongly supported by these observations.

One of the surprises from Galileo was that its orbit implied that Jupiter's solid core was much smaller than most people expected (and in fact would have been consistent with the complete absence of any core at all). Because of this I'm a bit sceptical about this paper, which suggests a much larger core than the Galileo results. The authors mention this point, and come up with an explanation involving distortion of the atmosphere by winds, but it strikes me as a bit contrived. Frankly I think the more likely possibility is that their theoretical model of the equation of state for hydrogen needs more work.

-- Ross Smith