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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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Midway Geyser Basin and the Grand Prismatic Spring, a hot spring located in Yellowstone National Park in the U.S. states of Wyoming and Montana. The third-largest hot spring in the world, it is known for its vivid colors, which are the result of pigmented bacteria in the microbial mats that grow around the edges of the mineral-rich water.

Photo credit: Mila Zinkova
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• Amphioctopus marginatus (pictured) is observed to store and modify coconut shells, assembling them to use as shelter, making it the first invertebrate known to use tools.
• NASA launches the Wide-field Infrared Survey Explorer to conduct an all-sky survey for infrared astronomy.
• China's President Hu Jintao, together with the leaders of Kazakhstan, Turkmenistan and Uzbekistan, inaugurates 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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From Wikipedia's newest articles:

• ... that Daulatpol gate in the Junagarh Fort (pictured) in India has 41 hand imprints of the wives of Maharajas of Bikaner, who committed sati (self-immolation) on the funeral pyres of their husbands?
• ... that British surgeon Theodore Dyke Acland was the son-in-law of Jack the Ripper suspect Sir William Gull?
• ... that male Coastal Petaltails have unique, bright orange anal appendages called 'petaltails' that are believed to be used to attract a mate?
• ... that the Texas mental health activist Helen J. Farabee was the first female student body president at a Big Ten university?
• ... that during the Six-Day War, the Golani Brigade participated in the battle of Tel Faher, where it lost 23 of its soldiers?
• ... that in North Korea, the question "How good was the taste of sungeoguk (trout soup)" is used as a common greeting to people returning from Pyongyang?
• ... that the most expensive dress owned by Maria Augusta, Duchess of Württemberg was worth 500 florins, more than 30 times a servant's annual income?
• ... that the entire collection of the Frissell Museum in San Pablo Villa de Mitla has disappeared?
  
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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).

More anniversaries: December 14 – December 15 – December 16