who determined that pluto is not a planet?
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In August 2006 the International Astronomical Union (IAU) downgraded the status of Pluto to that of “dwarf planet.” This means that from now on only the rocky worlds of the inner Solar System and the gas giants of the outer system will be designated as planets.
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Artist's rendition of our solar system. (Not to scale.) Ever since the discovery of Pluto in 1930, kids grew up learning that the solar system has nine planets.
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How Pluto Got its Name. Pluto is the only world (so far) named by an 11-year-old girl. In 1930, Venetia Burney of Oxford, England, suggested to her grandfather that the new discovery be named for the Roman god of the underworld. He forwarded the name to the Lowell Observatory and it was selected.
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The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.”
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Surface temp. Pluto (minor planet designation: 134340 Pluto) is an icy dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. ... That definition excluded Pluto and reclassified it as a dwarf planet.
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Pluto is the Roman form of the Greek god Hades. Hades is the Greek god of the dead and king of the underworld and Pluto is the Roman king of the underworld, god of the dead, and god of wealth. They're basically the same; Pluto is just Hades but more Roman.
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Mercury is not a dwarf planet because it has nothing in its orbit path. Mercury is over twice as dense, twice the diameter and about 30 times the mass of Pluto. Pluto is still a planet by the way, the real Planet Nine.
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NASA's New Horizons spacecraft is the first spacecraft to explore Pluto up close, flying by the dwarf planet and its moons on July 14, 2015.
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Pluto last crossed inside Neptune's orbit on February 7, 1979, and temporarily became the 8th planet from the Sun. Pluto will cross back over Neptune's orbit again on February 11, 1999 to resume its place as the 9th planet from the Sun for the next 228 years. ... The orbits never actually cross the same point in space.
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When Pluto was discovered 80 years ago, we never could have expected the variety of objects in the Solar System. Categorizing Pluto as a dwarf planet helps us better describe our celestial home. So, our Solar System now has eight planets, and five dwarf planets.
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Over 2,000 years ago, the Greek philosopher Aristotle had it all figured out. In his book On the Heavens, he wrote: "Again, our observations of the stars make it evident, not only that the Earth is circular, but also that it is a circle of no great size.
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After 1992, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt. In 2005, Eris, a dwarf planet in the scattered disc which is 27% more massive than Pluto, was discovered. ... That definition excluded Pluto and reclassified it as a dwarf planet.
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Pluto's active geology and dynamism is what allows for it to have an interior ocean, a multilayered atmosphere, organic compounds and evidence of ancient lakes and multiple moons. According to Metzger, the only planet that has more complex geology is planet Earth.
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The scientists argue that a planet should be defined only by its intrinsic properties, with the primary consideration being whether the object in question is big enough — and generates enough gravity — to organize itself into a roughly spherical shape. By this definition, Pluto is clearly a planet.
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Dwarf planets as 'plutoids' Pluto, Eris, Haumea and Makemake are all known as "plutoids," unlike the asteroidal dwarf planetoid Ceres. A plutoid is a dwarf planet with an orbit outside that of Neptune. Plutoids are sometimes also referred to as "ice dwarfs" due to their diminutive size and cold surface temperatures.
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The atmosphere of Pluto is the tenuous layer of gases surrounding Pluto. It consists mainly of nitrogen (N2), with minor amounts of methane (CH4) and carbon monoxide (CO), all of which are vaporized from their ices on Pluto's surface. ... Pluto is the only trans-Neptunian object with a known atmosphere.
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(In case you're wondering, though, Mercury is still significantly larger than the dwarf planet Pluto: Pluto's equatorial diameter is just 2,302 km, about half Mercury's width.)