If Pluto was considered too small to be a planet, why does Mercury still hold planet status?
919486
All of the above are incorrect in terms of the semantics of what "officially" makes a planet a planet. You need to look at the IAU (International Astronomical Union) definition of planet to see why Pluto is now defined as a dwarf planet\n\nFirst, why does Pluto not fit the IAU planet defintion?\n\n(1) A "planet"1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.\n\nPluto fails in "c".  Personally, I think "neighborhood" should be definined in terms of an orbital dynamics phase space since it never comes close to Neptune due to the 3:2 resonance  of their  orbits: my opinion and $3.95 will get you decaf latte at Starbucks. (Hmm... Neptune has not cleared Pluto out of ITS orbit either. . . maybe they know about some other icy bodies in Pluto's orbit?)\n\nPluto DOES meet the qualifications  for a dwarf planet.\n(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
547157
*Pluto: officially the 9th planet in our solar system\n*10th planet: nothing officially has this designation.\n\nIf you are talking about 2003 UB313, then there is a comparison to be made.  They both live in a similar part of the solar system, but it looks like UB313 seems to be a bit redder than Pluto.  Pluto is also known to have a transient atmosphere, not measurements of a potential atmosphere of UB313 have yet been published.
619708
Yes.  There is a large object (probably around 2000 kilometers in diameter) orbiting the Sun at a distance greater than Pluto's average distance from the Sun.  \n\nThe exact size of the object is unknown, and there is no official definition of "planet", so there is still some debate (as of February 2006) over whether this object should be considered a small planet or should be categorized as something else (such as a comet).
730339
1.  Pluto, Sedna, Eris, Ceres, etc. are still planets but they are a specific class of planets ("dwarf planets").  This is similar to the Sun being classifed as a "yellow dwarf" but it's still a star.\n\nNow that I've got that off my chest, Pluto and Sedna are members of the Kuiper Belt, a collection of bodies that extend from about Neptune's orbit out to where the Oort Cloud is supposed to begin.  The Kuiper Belt is approximately co-planar with the ecliptic but extends farther away from the central plane of the solar system.  This definition allows Pluto, whose orbital inclination is significantly larger than average to be included in the Kuiper Belt.\n\nAstronomers are consistently finding more members of the Kuiper Belt through photographic review.  Most are smaller than Pluto, Sedna and Eris, some are similar in size and there is likely to be at least one more body that will be larger.
3028
Xena.  Planet Xena and her moon Gabriella.  I'm not even kidding, that's what they named it.  There is current debate as to whether or not it is actually planet because it is so small and so far out, but on that note there is also debate still going as to whether pluto is actually a planet or not.  Really, it all depends on how you define planet.  As far as I can tell, the debate is mostly due to how small they are as to whether or not they're actually planets and not just planetoids.
761604
all i can say is that NOTHING HAS CHANGED. pluto is still a PLANET. a full blown, fully acceptable PLANET. it has its own moon (Charon) and therefore its own gravitational pull stong enough to attract and HOLD ON TO an object over half its own size and mass. show me any other "asteroid","stationary comet" or even another "planet" capable of such a feat. however, just because ASTRONOMERS deem pluto lesser than it is, has no effect what so ever on ASTROLOGERS exept to piss us off.
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.
47426
No. There have been a number of objects discovered recently in the outer solar system, including one which appears to be larger than Pluto. But unless something about the size of Neptune is found (which is possible) none of these are likely to gain official planet status.\n\nIn fact, in many respects Pluto should be "demoted," although that is not going to happen.\n\nThere isn't a real scientific definition of where the boundry is between a planet and, say, a moon, or a Kuiper object. For most objects it's clear what to call them, but for others the classification is ambigious. The reason being, of course, that our classifications are (somewhat) arbitrary and the solar system is composed of a continuum of objects of different sizes, in different orbits, etc.\n\nPluto was called a planet when it was discovered because a 9th planet was expected. Percival Lowell spent a long time looking for such a planet which he predicted from orbital irregularities he calculated with Neptune and Uranus. But he never found what he was looking for. Clyde Tombaugh, a couple of years later, resumed the search and eventually discovered Pluto. However, Pluto is much too small and in the wrong place to be Lowell's suspected planet. Lowell was probably just wrong in his calculations.\n\nBecause a 9th planet was expected and because in 1930 little could be told of Pluto's physical characteristics, I don't think anyone seriously doubted whether or not it should be classified as a planet. It seemed obvious, at the time, that it was.\n\nIn the 1950s and 1960s astronmers began to postulate that comets orginated from a vast pool of objects in the extreme distant regions of the solar system. This lead to the hypothesis of the Oort cloud, and the "closer" Kuiper belt (that being 50 - 100 AU from the Sun).\n\nIt wasn't until the 1990s that a lot of Kuiper-esque objects were actually discovered. (I hedge on the classification, because some objects similar in diamter, etc., have been found inside the orbit of Pluto.)\n\nIf in 1930 Clyde Tombaugh had an inkling of something like a Kuiper belt he probably would not have assumed that Pluto was a planet. If Pluto was discovered today it also would (probably) not be considered a planet.\n\nSo basically, if we could re-do history Pluto would be "demoted." On the other hand, there have been generations of kids who learned the whole 9 planets bit. Because of the the International Astronomical Union - the international organization in charge of naming things - has *officially* declared Pluto a planet. A link to their announcement is below.\n\nI suspect - and I am taking an educated guess - that the new objects in the outer solar system, even though slighly larger than Pluto - won't get "official" planet status.\n\nOf course the reality is more complex, and nature doesn't always fit neatly into human classification schemes.
2903
I quote : "Two small moons have been discovered orbiting Pluto, bringing the planet's retinue of known satellites to three and leaving scientist to wonder how it could be. ...The moons are catalogued as S/2005 P1 and S/2005 P2 for now. Once they are confirmed, the discoverers will suggest names, to be approved by the International Astronomical Union."\n\nFrom: http://www.space.com/scienceastronomy/051031_pluto_moons.html
487505
It's actually just a large asteroid, and they haven't decided whether to call it a planet yet. Problem is, they also discovered that Pluto is just a large asteroid, and if they disacknowledge the new planet, they would have to also disacknowledge Pluto.
716811
Its both ways actually-an asteroid and a planet.pluto circles the sun.this is the reason why its called a planet.but it also cuts across the eliptical orbit (if you know what i mean)while the others dont.There was a big debate on what pluto really was.anyway right now i think pluto is considered an asteroid and not a planet.
147445
Its all relative..usually we use sun as a point of a reference when we talk about relative size of planets which circle it. Pluto is about the same size as mercury.
186108
Ten. A new planet has been discovered that is approximately the same size as Pluto. It has not yet been formally named. Check http://www.nasa.gov/vision/universe/solarsystem/newplanet-072905-images.html for more info:)
760765
well, technically the last celestial body to be officially classified as a planet at the time was Pluto, but since it's demotion I'm not sure you can say that any more, so it's going to be Neptune in that case.
141708
Yes. It's actually in our own solar system.  Whether it is a planet or not is the real question.  It is really small.  While bigger than pluto, it is still smaller than the Earth's moon!
927189
To answer your second question first (I'm just an ornery cuss), Pluto is still a member of the Solar System. It's no longer considered a planet, though. It is now called a dwarf planet because of its size and extremely anomalous orbit (so look it up already).Just like the moon. asteroids, etc. it is still part of the Solar System.\n\nAs to the 1st part of your question-------Usually, as long as Mickey gives him table scraps instead of that crap from the can.Woof!Woof!
94846
First of all, Charon (Pluto's moon) is not bigger than Pluto.\nPluto has a diameter of about 2274 km and a mass of about 1.27 E22 kg.\nCharon has a diameter of about 1212 and a mass of about 1.90 E21 kg.\n\nBut even if a moon is larger than another celestial body, it should not automatically be bumped up to "planet status".\nAfter all, our moon ("the moon") is larger than pluto, but it is not a planet.