Project Proxima

A trip to Proxima Centauri @proximaspace

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Pluto is the largest object in the Kuiper belt, the tenth-most-massive known body directly orbiting the Sun, and the second-most-massive known dwarf planet, after Eris. Like other Kuiper belt objects, Pluto is primarily made of rock and ice, and is relatively small, about 1/6 the mass of the Moon and 1/3 its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU from the Sun. Hence Pluto periodically comes closer to the Sun than Neptune, but an orbital resonance with Neptune prevents the bodies from colliding.

Discovered in 1930, Pluto was originally considered the ninth planet from the Sun. Its status as a major planet fell into question following further study of it and the outer Solar System over the next 75 years. Starting in 1977 with the discovery of the minor planet Chiron, numerous icy objects similar to Pluto with eccentric orbits were found. The scattered disc object Eris, discovered in 2005, is 27% more massive than Pluto. The understanding that Pluto is only one of several large icy bodies in the outer Solar System prompted the International Astronomical Union (IAU) to formally define 'planet' in 2006. This definition excluded Pluto and reclassified it as a member of the new 'dwarf planet' category. Astronomers who oppose this decision hold that Pluto should have remained classified as a planet, and that other dwarf planets and even moons should be added to the list of planets along with Pluto.