This process is called mitosis. However, parental gametes  the sperm and egg cells  are unique from all other cells in that they reproduce through a process called meiosis. The purpose of meiosis is to shuffle genetic information and cut the cellular chromosome number in half, from 46 chromosomes to 23 chromosomes.
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered. Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun.
Pluto was a planet when New Horizons was launched. It's much like asking why there were missions sent to explore Mercury, Mercury is not complex from a geologic standpoint. Pluto was the final world, final planet before it got demoted, so people just wanted to send a mission to explore this planet.