continued… When Pluto was discovered in 1930, the scientific community agreed it was a planet. In 1987, another very large object was found in the Kuiper Belt. Since then, over a thousand more objects have been discovered. While Pluto was the largest, one named Eris has more mass and also has a moon. In 2006, the definition of planet was altered to be a celestial body that: a. is in orbit around the sun, b. has enough mass for its gravity that it has (nearly) a round shape and c. has cleared other large objects from the region of its orbit. Pluto did not meet criteria C. A new category was created: dwarf planet, which Pluto met the criteria for. Eris was also categorized as dwarf planets.
New Horizons was the first spacecraft to explore Pluto and its moons. It revealed that Pluto and moon Charon have dramatic landscapes and altered surfaces that were surprisingly young. It has passed Pluto and is currently in the Kuiper Belt.
The last “real” planet in our solar system is Neptune, and before it is Uranus. Uranus was discovered in 1781 by William Herschel, Neptune was discovered in 1846 by Johann Gottfried Galle. Both are icy gas giants, which means they have small rocky cores, but the majority of the planets are made up mostly of gas and ices — so they don’t have solid surfaces. Both are blue/green in color, which comes from high concentrations of methane. Both have faint rings — Uranus’s has thirteen and Neptune has six.
