Free Astronomy Magazine September-October 2015

SEPTEMBER-OCTOBER 2015 Al- ready by 15 July the first close-up images of Pluto's surface were avail- able, which, in an equato- rial area at the base of the “heart”, show a range of mountains with peaks as high as 3,500 metres, prob- ably originated not more than 100 million years ago, as further proof that Pluto's surface is one of the youngest of the en- tire solar system − a fact almost entirely unexpected. Taking into account the prop- er differences in proportion, a similar sce- nario applies to Charon, which in a very detailed image released in mid-July shows terrains that were formed relatively recent- ly, dotted by cliffs and troughs stretching 14 July, seven hours after closest approach, New Horizons passes behind Pluto and takes this pic- ture of the edge of theatmosphereback- lit by the sun, dis- covering that it is much more extend- ed than previous- ly believed. In the video below, a vir- tual flyby of Norgay Montes and Sput- nik Planum. [NASA/ Johns Hopkins Uni- versity Applied Physics Laboratory/ Southwest Re- search Institute] as far as a thousand kilometres, suggesting extensive fractur- ing of the satellite’s crust, as a result of in- ternal geological processes. In the days following the flyby, back to Earth also began to arrive data and im- ages taken by other instruments aboard the spacecraft, such as those produced by the Alice spectrograph, which demon- strate how Pluto’s upper atmosphere is overall much more extended into space than previously thought: 1,600 km instead of 270 km. This new measurement is the result of a Sun-Pluto-spacecraft alignment, carefully planned in order to backlit its at- mosphere to investigate it better. Observations made with the Solar Wind Around Pluto instrument have instead shown that Pluto's atmosphere is constant- ly being stripped of gas by the solar wind action, that with its pressure forms behind the planet a tail extending over 100,000 km. The fact that despite this phenome- non Pluto still has an atmosphere means that the gas making it up is being contin- uously replenished by geological process-