Pluto (Dwarf Planet/Plutoid)

Pluto (DwarfPlanet/Plutoid)

Named after the Roman god of the underworld, Pluto discovered on February 18, 1930, and originally considered the ninth "planet" [1] was demoted to the status of "dwarf planet" [2] by the International Astronomical Union on August 24, 2006, and further redefined as a "plutoid" [3] on June 11, 2008. [4]

Pluto is the second largest of the dwarf planets (still open to debate), its diameter of approximately 2,320 kilometers slightly less than that of Eris and roughly 19 percent that of Earth.

Pluto has a thin atmosphere, which due to an eccentric orbit 29.66 AU at perihelion and 49.31 AU at aphelion (1 AU being the distance between the Sun and the Earth, approximately 150,000,000 kilometers.) forms when frozen methane, nitrogen and carbon dioxide on its surface sublimates into gas upon solar approach, refreezing again as it retreats outward. The mean surface temperature is -225 °Celsius.

Pluto’s composition is still unknown, the best guess being a rocky, silicate and water ice core surrounded by a layer of water ice in turn covered by a layer of frozen methane.

New Horizons the first mission in NASA's New Fontiers programme, launched January 19, 2006, will reach its closest approach to Pluto on July 14, 2015, the first Earth vessel to draw near that forbidding object. Armed with a remote sensing package, it will photograph and examine the atmosphere, geology and morphology of both the planet and its largest moon.

If Pluto is indeed the god of the underworld then this planet is well named, for the chances of their being indigenous life on this frigid orb are slim indeed.

As an interesting aside the ashes of Clyde Tombaugh, Pluto’s discoverer, are on board the New Horizons spacecraft.

To date Pluto has four known moons: Charon, Nix, Hydra and S/2011 P1 or P4 (interim).

[1] A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape) and (c) has cleared the neighborhood around its orbit.

[2] A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape), (c) has not cleared the neighborhood around its orbit and (d) is not a satellite.

[3] A "plutoid" is a trans-Neptunian dwarf planet.

[4] Due to its position in the Kuiper belt (sometimes called the Edgeworth-Kuiper belt) [5] Pluto along with Haumae and Makemake is also classified as a Kuiper belt object or KBO.

[5] The Kuiper belt is a region of the outer Solar System populated by billions of rock-ice objects. It reaches from the orbit of Neptune (30 AU) outward to approximately 55 AU.

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