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Journey to the center of Jupiter

Most school children learn that the giant planet Jupiter is a "gas giant". This means that the largest planet in our solar system is composed mostly of gases such as hydrogen and helium. Well, just as our definitions of what a planet is-as in the case of Pluto-are being redefined, we may have to refine our definition of what a gas giant planet is.

A discovery made just last month has revealed that Jupiter has a rocky core more than twice as large as previously measured. This makes big Jupiter appear less like a gas giant and more like a quasi-terrestrial planet, at least deep below its ultra-dense atmosphere.

A research team led by Burkhard Militzer at the University of California ran a series of detailed computer simulations that showed how individual hydrogen and helium, at the atomic scale, behave deep inside Jupiter. Hydrogen-helium atoms behave strangely in the extreme pressure and temperature environment of the big outer planets.

Militzer's colorful computer model shows that the inner of Jupiter core is an immense rock approximately 16 times Earth's mass. This rocky core, perhaps made of iron, nickel and silicate materials, amounts to five percent of Jupiter's total mass. The new model challenges the old, standby theories: Most astronomers thought Jupiter's core was either seven Earth masses or they argued that the big planet lacked any kind of core except for maybe a mushy interior.

According to an interview with Space.com, Militzer said his team's high-tech simulations show a big rocky object in Jupiter's central region surrounded by an ice layer. Little ice exists on the planet beyond the core region; this is contrary to a theory apparently overturned by last week's discovery.

"This is a very different result for the interior structure of Jupiter than other recent models, which predict a relatively small or hardly any core and a mixture of ices throughout the atmosphere," Militzer told Space.com.

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