In this image from March 25, 2007, a thin band of white clouds is shown above Jupiter's equator. The white color indicates clouds at higher altitudes in Jupiter's atmosphere. (Xinhua/Reuters Photo) Photo Gallery>>>

    WASHINGTON, Nov. 25 (Xinhua) -- Jupiter has a rocky core that is more than twice as large as previously thought, according to computer calculations by a team of international researchers.

    They simulated conditions inside the planet on the scale of individual hydrogen and helium atoms. And their results were published Tuesday in Astrophysical Journal Letters.

    They first calculated the properties of hydrogen and helium for temperature, density and pressure at the surface all the way to the planet's center. Then using the theoretical data, they build anew model for Jupiter's interior.

    A comparison of this model with the planet's known mass, radius, surface temperature, gravity and equatorial bulge implies that Jupiter's core is an Earth-like rock 14 to 18 times the mass of the Earth, or about one-twentieth of Jupiter's total mass. Previous models predicted a much smaller core of only seven Earth masses, or no core at all.

    The simulation suggests that the core is made of layers of metals, rocks and ices of methane, ammonia and water, while above it is an atmosphere of mostly hydrogen and helium. At the center of the rocky core is probably a metallic ball of iron and nickel, just like Earth's core.

    "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," said the authors.

    The large, rocky core implies that as Jupiter and other giant gas planets formed 4.5 billion years ago, they grew through the collision of small rocks that formed cores that captured a huge atmosphere of hydrogen and helium.

    In the future, the researchers plan to use the new model to simulate other planets' interiors, and to investigate the implications for the formation of planets outside our solar system.

    Future data from NASA's Juno mission, to be launched in 2011 and orbit Jupiter by 2016 to measure the planet's magnetic field and gravity, will provide a check on the new model's prediction.