The magnetosphere of Jupiter is the cavity created in the solar wind by the planet's immensely strong magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of 1950s and was directly observed by the Pioneer 10 spacecraft in 1973. Jupiter's internal magnetic field is generated by electrical currents flowing in the planet's outer core, which is composed of metallic hydrogen. Volcanic eruptions on Jupiter's moon Io eject large amounts of sulfur dioxide gas into space, forming a large torus around the planet. Jupiter's magnetic field forces the torus to rotate with the same angular velocity and direction as the planet's rotation. The torus in turn loads the magnetic field with plasma, in the process stretching it into a pancake-like structure called a magnetodisk. (more...)

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From Wikipedia's newest articles:

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• NASA launches the Wide-field Infrared Survey Explorer to conduct an all-sky survey for infrared astronomy.
• China's President Hu Jintao (pictured), together with the leaders of Kazakhstan, Turkmenistan and Uzbekistan, inaugurate the Central Asia – China gas pipeline.
• U.S. economist Paul Samuelson, a Nobel laureate and one of the founders of neo-Keynesian economics, dies at the age of 94.
• The Constitutional Court of Turkey bans the Democratic Society Party over the party's alleged links to the Kurdistan Workers' Party.
• The United Nations Climate Change Conference opens in Copenhagen, Denmark.
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December 15: Zamenhof Day

• 1467 – Troops under Stephen III of Moldavia defeated the forces of Matthias Corvinus of Hungary in present-day Baia, Romania.
• 1791 – The first ten amendments to the United States Constitution, collectively known as the United States Bill of Rights, were ratified.
• 1864 – American Civil War: Union troops essentially destroyed the Army of Tennessee, one of the largest Confederate forces, at the Battle of Nashville.
• 1942 – World War II: The Americans engaged Imperial Japanese forces at the Battle of Mount Austen, the Galloping Horse, and the Sea Horse in the hills near the Matanikau River area on Guadalcanal during the Guadalcanal Campaign.
• 1964 – The six-month long Canadian Great Flag Debate effectively ended when the Canadian House of Commons voted to replace the de facto national flag of Canada, the Canadian Red Ensign, with an official one designed by historian George Stanley, the Maple Leaf Flag (pictured).
• 2005 – The F-22 Raptor, a Stealth fighter aircraft that the United States Air Force claimed is unmatched by any known or projected fighter, entered into service despite a protracted and costly development period.

More anniversaries: December 14 – December 15 – December 16