Callisto is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. It does not form part of the orbital resonance that affects three inner Galilean satellites—Io, Europa and Ganymede—and thus does not experience appreciable tidal heating. Callisto rotates synchronously with its orbital period, so the same face is always turned toward Jupiter. Callisto is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3. Compounds detected spectrally on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters and associated scarps, ridges and deposits. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere.
Read the rest of this article: http://en.wikipedia.org/wiki/Callisto_%28moon%29
_______________________________ Today's selected anniversaries:
1791:
French inventor Claude Chappe and his brothers first demonstrated the semaphore line, a signaling system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles. http://en.wikipedia.org/wiki/semaphore_line
1836:
Texas Revolution: At a convention in Washington-on-the-Brazos, the Mexican state of Texas adopted a declaration of independence from Mexico, establishing the Republic of Texas. http://en.wikipedia.org/wiki/Republic_of_Texas
1877:
The U.S. Electoral Commission awarded twenty disputed electoral votes to Rutherford B. Hayes, thus assuring his victory in the 1876 U.S. presidential election. http://en.wikipedia.org/wiki/United_States_presidential_election%2C_1876
1970:
Rhodesia formally broke its links with the British crown and declared itself a republic. http://en.wikipedia.org/wiki/Rhodesia
1978:
Aboard the Soviet spacecraft Soyuz 28, Czech Vladimír Remek became the first person not from the Soviet Union or the United States to go into space. http://en.wikipedia.org/wiki/Soyuz_28
2009:
President of Guinea-Bissau João Bernardo Vieira was assassinated in an attack by a group of soldiers on his private residence in Bissau. http://en.wikipedia.org/wiki/Jo%C3%A3o_Bernardo_Vieira
_____________________________ Wiktionary's word of the day:
gourmand (n): 1. A person given to excess in the consumption of food and drink; a greedy or ravenous eater. 2. A person who appreciates good food http://en.wiktionary.org/wiki/gourmand
___________________________ Wikiquote quote of the day:
In times like these, it's helpful to remember that there have always been times like these. --Paul Harvey http://en.wikiquote.org/wiki/Paul_Harvey