Free Astronomy Magazine September-October 2015

SEPTEMBER-OCTOBER 2015 tellites Nix and Hydra, which allowed to distinguish areas of different chemical- mineralogical composition and determine more precisely the size of the two objects, whose shape is clearly irregular: Nix is 42 km long and 36 km wide, while Hydra is 55 km long and 40 km wide. By mid-Octo- ber, New Horizons will also send images and data regarding Pluto’s two smallest satellites, Styx and Kerberos. On 20 July arrives to Earth what is so far one of the most significant images trans- mitted by the spacecraft and released to the public, showing a southern portion of the Tombaugh Regio, provisionally named Sputnik Planum, on whose western edge can be clearly seen a new mountain range with peaks about 1,500 metres high, but above all can be observed the unmistak- able traces of the progression of deposits of light-coloured and likely recent mate- rials towards more darker, definitely older terrains, something similar to a huge gla- cier of flowing hydrocarbons that in its path has also filled the bottom of some craters. This is for now the final proof that Pluto is still a geologically active world in which the heat produced by the radioac- tive decay of elements inside it seems to play a dominant role. n