LYCOS RETRIEVER 
Pluto
built 641 days ago
Explanation: In 1930, tiny, icy world Pluto was discovered orbiting in the distant solar system. In 1978, its relatively large companion Charon was detected by ground-based observations. This year, the Hubble Space Telescope may well have detected two further members of the Pluto system. Provisionally designated S/2005 P1 and S/2005 P2, the two potential new moons are seen orbiting in a counterclockwise direction about 44,000 kilometers (27,000 miles) from Pluto in these deep Hubble images recorded only three days apart. The diminutive and faint companions are ... apparently detected on Hubble images of Pluto from 2002, but this coming February follow-up observations are planned in an effort to confirm the discovery of the new moons. Compared to Pluto's and Charon's diameters of 2,300 and 1,300 kilometers respectively, these moons are estimated to be between 60 and 200 kilometers across.
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At the time these images were taken, Pluto was a magnitude 13.8 object. Pluto was the smallest planet in the solar system, until it was officially demoted on August 24, 2006, to the status of a "dwarf planet." Pluto is no longer considered to be a major planet. Pluto differs from the eight major planets in almost every respect. Pluto's orbit is so excentric that it swings inside the orbit of Neptune during a relatively small portion of its 248 year orbit around the sun. Between 1980 and 1999, Pluto was closer to the sun than Neptune. In March 1999, Pluto crossed back over Neptune's orbit and is now more distant than Neptune and will be for more than 200 years until it again swings inside of Neptune's orbit.
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Pluto has one natural satellite, Charon, first identified in 1978. Pluto and Charon are noteworthy for being the only planet/moon pair in the solar system whose barycenter lies above the planet's surface. Pluto and Charon are ... unusual among planets in that they are tidally locked to each other. This means that Charon always presents the same face to Pluto, and Pluto also always presents the same face to Charon. Note that some binary asteroids may also possess both of these traits, and that the Jupiter/Sun barycenter is above the Sun's surface, so neither is completely unique.
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Once known as the smallest, coldest, and most distant planet from the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930. On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet. According to the new rules a planet meets three criteria: it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and 2003UB313 (Eris), which orbit among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.
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Pluto's highly eccentric orbit makes it the eighth-most distant planet from the Sun for part of each orbit; this most recently occurred from February 7, 1979 through February 11, 1999. Pluto orbits in a 3:2 orbital resonance with Neptune. When Neptune approaches Pluto from behind their gravity start to pull on each other slightly, resulting in an interaction between their positions in orbit of the same sort that produces Trojan points. Since the orbits are eccentric, the 3:2 periodic ratio is favoured because this means Neptune always passes Pluto when they're almost farthest apart. Half a Pluto orbit later, when Pluto is nearing its closest approach, it initially seems as if Neptune is about to catch up to Pluto. But Pluto speeds up due to the gravitational acceleration from the Sun, stays ahead of Neptune, and pulls ahead until they meet again on the other side of Pluto's orbit.
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A proposed expedition to Pluto to observe its atmosphere before it freezes is in danger of cancellation. At a distance from the sun that is 40 times further than Earth, the Pluto / Charon double planet is the last remaining planet unvisited by probes from Earth. The mission to Pluto and possibly other Kuiper Belt objects is threatened. Advanced technologies such as a lightweight radiation hardened electronics are proving harder to develop than originally anticipated. NASA ... hoped to use a radioisotope power source three times more efficient than current systems. A third problem is delays in the creation of the Evolved Expendable Launch Vehicle program, which was to have been used to carry the probe to space in December of 2004.
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