Only one planet in our Solar System has not been visited by a robotic craft from Earth. Which is it?
929479
Pluto, although New Horizons is on its way and will fly by in 2015.
33502
None, but there are nine planets in the solar system that Earth is part of.
556954
there are nine planets in the solar system. it is not know yet how many planets are there in the entire universe, because we just know about 3 galaxies (and still do not know about any planets in galaxies other than the milky way)
741583
You are right.  Neptune and Uranus have only been visited by Voyager 2.  Jupiter and Saturn have been visited by multiple probes however.
604663
There are ten planets in our solar system namely mercury,venus,earth mars,jupiter,saturn,uranus,neptune,pluto\nand\n2003-UB313 is the official name of the object that is considered to be a contender for the title of "10th planet". As of August 1st, 2005 the IAU has yet to confirm whether this object will be officially be recognized as the 10th planet in our solar system. This little page will follow events and provide more information when available.\nOfficial Name:  2003 UB313  \nProposed Name:  Unknown\nThe name Xena is rumored to be the name submitted to the IAU for approval, althought there is no official confirmation of the name. "..that was our tongue-in-cheek internal name, never intended for public consumption," says Professor Brown \nDiscovered By: Michael Brown, professor of planetary astronomy at California Institute of Technology (Caltech) and colleagues Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University.\n\nFirst photographed in 2003 using a 122cm telescope at the Palomar Observatory. \n \nEstimated Size:  approx 2700 km (1,700 miles) in diameter\nThis is the estimate as of August, 2005. From Wikipedia - Although the object's diameter is not yet well determined, it is estimated to be between 2,390 and 3,550  km . The amount of light it reflects (its albedo ) seems to be quite high, and initial observations show that methane ice is present on the object's surface. Both these properties make it more similar to Pluto than previously discovered large outer solar system planetoids .  \nOrbit: 560 years \nestimated one solar orbit per 560 years.  \nDistance from Sun:\n approx 9 billion miles / 14.4 billion km\nThis is around 100 times the Earth's distance, or 3 times Pluto's distance from the Sun. \nWhere is it Now?  At present, it is near its farthest point from Earth, but in about 280 years, it will be as close as Neptune, (the eighth planet, discovered in 1846).
584504
10 is my answer. A new planet call UB313 was discovered. Here are they planets in order:\nMecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.\n\n10 Planets said. 10 Points for the best answer
265889
okay lets clear this matter!  We do have one spacecraft that has left our solar system, and that is Voyager 1.  Voyager 1 gave us a complete picture of our solar system by way of Neptune's Orbit.  Neptune's orbit allowed the spacecraft to venture 6.4 kilometers outside our solar system, and return back.  Voyager 1 was an exploration that gave us vast information about our solar system, but more importantly it gave us the only close up images of pluto we have to date.  However 6.4 kilometers is not enough to give us a picture of the milky way.  So Nasa uses Cosmic Background Explorer's (COBS) Diffuse Infrared Background Experiment (DIRBE) to combine images obtained at several near-infrared wavelengths.  These wavelengths are gathered from light wavelengths from neighboring stars that look directly into our galaxy.  So all images therefore are from a distance looking at our solar system from the outside.
1070271
The new planet is the most distant object ever seen in orbit around the sun, even more distant than Sedna, the planetoid discovered almost 2 years ago. It is almost 10 billion miles from the sun and more than 3 times more distant than the next closest planet, Pluto and takes more than twice as long to orbit the sun as Pluto.
888333
NASA is not involved in the SETI project at all.  All of the funding is private.
35874
In our Solar System, there are eight official planets, nine if you count Pluto (whose status is being debated).  \n\nAs for the rest of the universe, it is difficult to say, but it is reasonable to assume that planet formation from leftover stellar material is relatively common.  Astronomers usually detect large gaseous planets (like Jupiter) by the slight wobble of the star's motion due to the gravity of the planet, so currently it is almost impossible to detect small planets.\n\nAs of November 2005, there were 164 confirmed extrasolar planets.
542914
There are two ways to answer your question - \n\nThe orbit of Venus is closest to the orbit of Earth.\n\nHowever, depending on the current positions of the planets in their relative orbits... Mars or Mercury could be closest to Earth.\n\nToday, it appears that Venus is the closest planet.\n\nTwo months from now, Mercury will be the closest planet to Earth.\n\nSee the attached link for a pretty nifty orbit simulator from the NASA /JPL website.
1052164
Ask those living in other planets!
983443
Pluto. \n\nThe International Astronomical Union (IAU), at a meeting in August 2006, voted on their first "official" definition of a planet. Based on this new definition, Pluto is no longer a planet. According to the IAU's definition, our Solar System has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. In the new scheme, Pluto will be one of several "dwarf planets" in the Solar System; but "dwarf planets" are not considered true planets. THere is still a lot of disagreement within the community on the definition of a planet.\n\nHere's the definition of a planet (found at wikipedia): \n\nThe International Astronomical Union defines "planet" as a celestial body that, within the Solar System,\n\n(a) is in orbit around the Sun; \n(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape; and \n(c) has cleared the neighbourhood around its orbit; \nor within another system, \n\n(Pluto fails to meet the third condition above)\n\n(i) is in orbit around a star or stellar remnants; \n(ii) has a mass below the limiting mass for thermonuclear fusion of deuterium; and \n(iii) is above the minimum mass/size requirement for planetary status in the Solar System.
915328
By your criteria, Mercury, Venus, Mars, Saturn, Jupiter, Neptune, and Uranus are not planets.\n\nMercury has no atmosphere and therefore no weather or vegetation.\nVenus has no vegetation.  It's 900 degrees on the surface!\nMars has no vegetation, no liquid, and no magnetic field.\nSaturn & Jupiter are gas giants and have no vegetation.\nNeptune and Uranus are mostly gas and do not have vegetation.\n\nThus, by your criteria, Earth is the only planet.\n\nI did not consider "internal plumbing" because the term is too vague.
13099
I DONT THINK THAT WE R  ALONE . WE HAVE SEEN A FEW SIGNS OF XTRA TERRESTRIAL LIFE AND IT  IS POSSIBLE THAT THERE ARE OTHER LIVING ORGANISMS INHABITED PLANETS
483328
the planet?Pluto is the farthest planet from the Sun (usually) and by far the smallest. Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton). \n\n        orbit:    5,913,520,000 km (39.5 AU) from the Sun (average)\n        diameter: 2274 km\n        mass:     1.27e22 kg\nIn Roman mythology, Pluto (Greek: Hades) is the god of the underworld. The planet received this name (after many other suggestions) perhaps because it's so far from the Sun that it is in perpetual darkness and perhaps because "PL" are the initials of Percival Lowell. \nPluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway. \nAfter the discovery of Pluto, it was quickly determined that Pluto was too small to account for the discrepancies in the orbits of the other planets. The search for Planet X continued but nothing was found. Nor is it likely that it ever will be: the discrepancies vanish if the mass of Neptune determined from the Voyager 2 encounter with Neptune is used. There is no Planet X. But that doesn't mean there aren't other objects out there, only that there isn't a relatively large and close one like Planet X was assumed to be. In fact, we now know that there are a very large number of smaller objects in the Kuiper Belt beyond the orbit of Neptune. \nPluto is the only planet that has not been visited by a spacecraft. Even the Hubble Space Telescope can resolve only the largest features on its surface (left and above). A spacecraft called New Horizons was launched in January 2006. If all goes well it should reach Pluto in 2015. \nFortunately, Pluto has a satellite, Charon. By good fortune, Charon was discovered (in 1978) just before its orbital plane moved edge-on toward the inner solar system. It was therefore possible to observe many transits of Pluto over Charon and vice versa. By carefully calculating which portions of which body would be covered at what times, and watching brightness curves, astronomers were able to construct a rough map of light and dark areas on both bodies. \nIn late 2005, a team using the Hubble Space Telescope discovered two additional tiny moons orbiting Pluto. Provisionally designated S/2005 P1 and S/2005 P2, they will be assigned real names when the discovery is confirmed. They are estimated to be between 60 and 200 kilometers in diameter. \nPluto's radius is not well known. JPL's value of 1137 is given with an error of +/-8, almost one percent. \nThough the sum of the masses of Pluto and Charon is known pretty well (it can be determined from careful measurements of the period and radius of Charon's orbit and basic physics) the individual masses of Pluto and Charon are difficult to determine because that requires determining their mutual motions around the center of mass of the system which requires much finer measurements -- they're so small and far away that even HST has difficulty. The ratio of their masses is probably somewhere between 0.084 and 0.157; more observations are underway but we won't get really accurate data until a spacecraft is sent. \nPluto is the second most contrasty body in the Solar System (after Iapetus). \nThere are some who think Pluto would be better classified as a large asteroid or comet rather than as a planet. Some consider it to be one of the larger Kuiper Belt objects (also known as Trans-Neptunian Objects). There is considerable merit to the latter position, but historically Pluto has been classified as a planet and it is very likely to remain so. Further complicating the situation, one such object (2003UB313) was recently discovered that is almost certainly larger than Pluto. Should it, too, be classified as
53486
Well, there's nine so far - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.  However, scientists have discovered other planets that orbit our Sun that are even further out than Pluto!  So there's a possibility that we may update our information involving the solar system sometime in the future....