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Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume, by a small margin, but is less massive than Eris.
For almost 50 years, Pluto was thought to be larger than Mercury, [6] [7] but with the discovery in 1978 of Pluto's moon Charon, it became possible to measure Pluto's mass accurately and to determine that it was much smaller than initial estimates. [8] It was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet.
Pluto is so small and so remote from the Sun and the Earth that it was not discovered until 1930. [3] It was classified as a planet at the time and remained as such for 76 years until 2006, when the International Astronomical Union reclassified it as a dwarf planet, as it belongs to a belt of many similar small objects. [4]
Pluto was considered a planet up until 2006, when researchers at the International Astronomical Union voted to "demote" it to dwarf planet.
The distance between Charon and Pluto is about 12,200 miles (19,640 km), compared to the 238,855 miles (384,400 km) on average separating Earth from its moon. ... "Every small body in the outer ...
They determined Pluto's mass to be 1.31×10 22 kg; roughly one five-hundredth that of Earth or one-sixth that of the Moon, and far too small to account for the observed discrepancies in the orbits of the outer planets. Lowell's prediction had been a coincidence: If there was a Planet X, it was not Pluto.
The definition of a planet has been a hot topic ever since a change kicked Pluto out of our planetary lineup in 2006. Now, a group of researchers is proposing a new definition yet again—one with ...
Disintegrating planetesimal, likely one of several orbiting its star. Likely about one-tenth the mass of Ceres and ~200 km in radius. [4] Ceres: 0.0742 Shown for comparison: Pluto: 0.1863 Shown for comparison: Moon: 0.2725 Shown for comparison: Kepler-37b: 0.3098 +0.0059 −0.0076: Smallest known exoplanet. [5] [6] BD+05 4868 Ab ~0.314