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Space Pictures / Pluto and Charon (Update)

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Title: Pluto & Charon

Source: Hubble Space Telescope

Information: Pluto - the "Double Planet" NASA's Hubble Space Telescope has obtained the clearest pictures ever of our solar system's most distant and enigmatic object; the planet Pluto, using the European Space Agency's Faint Object Camera. A recent Faint Object Camera image of Pluto and Charon is shown in the upper right hand frame of the photograph. This image is the first long duration HST exposure ever taken of a moving target. In order to avoid smearing of the images, ground controllers had to pre-program the Hubble Telescope spacecraft to track Pluto extremely accurately and compensate exactly for the "parallax" introduced by the combined motions of Pluto, the Earth, and the Hubble Telescope in their respective orbits. Pluto is currently near its closest approach to the Earth in its 249 year journey around the Sun, and is approximately four and a half billion kilometers away. The bright object at the center of the frame is Pluto while Charon is the fainter object in the lower left. Charon is fainter than Pluto because it is smaller and, probably, because its surface is covered by water and ice whereas Pluto is thought to be covered mainly by the more reflective methane frost or snow. As indicated in the diagram at the bottom of the photo, Charon's orbit around Pluto is a circle seen nearly edge on from the Earth, with a radius of almost twenty thousand kilometers - distance equal to approximately one and a half times the diameter of the Earth. At the time of observation, Charon was near its maximum apparent distance from Pluto, so that its angular separation was about nine tenths of an arc second. Because of the peculiar orientation of the Pluto-Charon orbit with respect to our line of sight, Charon approaches to within less than one tenth of an arc second of Pluto every three days.