A WORLD OF MYS­TERY

Our knowl­edge of Pluto’s prop­er­ties has grown a lot since 1930, but gaps re­main

Sky at Night Magazine - - PLUTO’S HISTORY -

Pluto Pluto is the largest mem­ber of the Kuiper Belt and part of a group of ob­jects known as Trans-Nep­tu­nian bod­ies. Th­ese ob­jects will re­veal a lot about con­di­tions in the early So­lar Sys­tem. Pluto has five satel­lites, the largest be­ing Charon, at just over half Pluto’s di­am­e­ter. The other four are Nix, Hydra, Ker­beros and Styx. Pluto’s or­bit is more like a comet’s: it is in­clined by 17º to the eclip­tic. At times it is closer to the Sun than Nep­tune. Pluto’s thin at­mos­phere is com­posed of ni­tro­gen, methane and car­bon diox­ide. Re­mark­ably, there is some ev­i­dence of winds blow­ing in the at­mos­phere. Pluto’s sur­face varies greatly in bright­ness and colour. Patches of red, grey and white give Pluto’s sur­face as much con­trast as the Satur­nian moon Iape­tus. It’s thought that Pluto’s at­mos­phere could col­lapse and freeze as the dwarf planet moves far­ther away from the Sun; it is not known whether there enough heat to pre­vent this. Be­tween 1994 and 2002/2003 some of Pluto’s sur­face fea­tures ap­peared to change, with the north­ern po­lar re­gion bright­en­ing up and the over­all red­dish hue of the sur­face in­creas­ing.

Hydra Nix Styx Charon Ker­beros Pluto has five known moons, the lat­est – Styx – only dis­cov­ered in 2012

2002/2003 Im­ages from Hub­ble show sur­face fea­tures chang­ing over eight years

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