Other objects in the Solar System incude dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids. Planet or Dwarf Planet? From the time it was discovered in 1930 until 2006, Pluto was considered the ninth planet in our solar system. When astronomers first observed Pluto, telescopes were not as powerful as they are now, so Pluto and its moon Charon were thought to be one larger object. With stronger telescopes, astronomers realized that Pluto was much smaller than they had thought. Over time, astronomers learned more about Pluto and found that it... Show more Other objects in the Solar System incude dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids. Planet or Dwarf Planet? From the time it was discovered in 1930 until 2006, Pluto was considered the ninth planet in our solar system. When astronomers first observed Pluto, telescopes were not as powerful as they are now, so Pluto and its moon Charon were thought to be one larger object. With stronger telescopes, astronomers realized that Pluto was much smaller than they had thought. Over time, astronomers learned more about Pluto and found that it differed from the other planets in additional ways. For example, unlike the outer planets, which are gas giants, Pluto is icy and rocky. Pluto’s orbit is also tilted relative to the orbits of the other planets, and its orbit is longer and narrower. Scientists also discovered that Pluto’s orbit is part of the Kuiper belt, a distant region of the solar system where more than 200 million small objects orbit the sun. Astronomers began to debate whether Pluto and other newly discovered, similar objects should be classified as planets. They decided that they needed to refine their definition of planet. According to the new definition, a planet must: - orbit a star rather than another planet so it is not a moon. - be small enough that it isn’t a star. - have enough mass that its gravity pulls it into a spherical shape. - have enough gravity to have cleared its orbit of smaller objects. Pluto does not fit the revised definition of a planet. It meets the first three criteria in the list above, but as part of the Kuiper belt, it does not meet the fourth criterion. To classify Pluto and similar orbiting objects, astronomers came up with a new category, the dwarf planet. A dwarf planet is an object that meets all the criteria of a planet except for clearing its orbit of other objects. In addition to Pluto, there are currently three other known dwarf planets in the solar system: Eris, Ceres, and Makemake. Show less
Other objects in the Solar System incude dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids.
Planet or Dwarf Planet? From the time it was discovered in 1930 until 2006, Pluto was considered the ninth planet in our solar system. When astronomers first observed Pluto, telescopes were not as powerful as they are now, so Pluto and its moon Charon were thought to be one larger object. With stronger telescopes, astronomers realized that Pluto was much smaller than they had thought. Over time, astronomers learned more about Pluto and found that it differed from the other planets in additional ways. For example, unlike the outer planets, which are gas giants, Pluto is icy and rocky. Pluto’s orbit is also tilted relative to the orbits of the other planets, and its orbit is longer and narrower. Scientists also discovered that Pluto’s orbit is part of the Kuiper belt, a distant region of the solar system where more than 200 million small objects orbit the sun. Astronomers began to debate whether Pluto and other newly discovered, similar objects should be classified as planets. They decided that they needed to refine their definition of planet.
According to the new definition, a planet must: - orbit a star rather than another planet so it is not a moon. - be small enough that it isn’t a star. - have enough mass that its gravity pulls it into a spherical shape. - have enough gravity to have cleared its orbit of smaller objects.
Pluto does not fit the revised definition of a planet. It meets the first three criteria in the list above, but as part of the Kuiper belt, it does not meet the fourth criterion. To classify Pluto and similar orbiting objects, astronomers came up with a new category, the dwarf planet. A dwarf planet is an object that meets all the criteria of a planet except for clearing its orbit of other objects. In addition to Pluto, there are currently three other known dwarf planets in the solar system: Eris, Ceres, and Makemake.
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