Which man-made object is 3.2 billion miles away and getting more distant every day? Yes, it's the New Horizons spacecraft, which grabbed the headlines in July when it made its closest approach to the dwarf planet Pluto . Although it is now far beyond Pluto on its way to its next target, it is still sending back incredible images (the vast distance means that sending just one image takes over 4 hours, so it will be well over a year before all the data collected at Pluto finally makes it back to Earth.)
This time last year the best available images of Pluto were little more than a blurry blob. Compare that with this image where the level of detail is astounding, revealing fascinating features with a very alien appearance - mountains made of solid blocks of ice, crushed up together in the top left half, in stark contrast to the white plain of smooth ice on the bottom right, with its striking cell-like features.
Blue haze
This image shows something that was totally unexpected: Pluto has blue skies! Or at least, a high level haze made up of tiny particles that scatter blue light, just as the particles in earth's atmosphere do. Pluto's blue sky is not an atmosphere though – scientists believe that the haze is composed of soot-like particles that are formed by chemical reactions of nitrogen and methane, triggered by ultraviolet sunlight. As the particles grow they become heavier and gradually settle onto Pluto's surface.
New Horizons also spotted two large mountains several miles high with apparent hole-like depressions at the top – they look very like volcanoes on earth! But unlike terrestrial volcanoes, these mountains are made not of rock but of solid ice, and if they are actually volcanoes, they would be 'cryovolcanoes', belching out not molten lava, but a sort of semi-frozen ice sludge of ice made of water, nitrogen, ammonia or methane.
Binary planets
The spacecraft did not just image Pluto itself, but also its family of moons. The largest, Charon, is huge for a moon, being an eighth of its companion's mass and nearly half as wide, and it seems that the two actually orbit each other, making the pair the first ever known binary planet system. The other moons, Nix, Hydra, Kerberos and Styx, are a mixed bunch, much smaller with odd shapes and chaotic orbits that are difficult to predict, caused to the complex gravitational forces originating in the binary system.
Next target
New Horizons has now left Pluto behind - in October and November NASA's engineers carried out a series of extraordinarily precise remote manoeuvres, positioning it on exactly the right course for its next target nearly a billion miles more distant, one of the objects in the Kuiper Belt, a region of thousands of icy objects at the far edge of the solar system that is believe to be a nursery for comets. Who knows what it will discover there...
www.nasa.gov/nh/nh-finds-blue-skies-and-water-ice-on-pluto
http://www.space.com/29559-pluto-moons-weird-orbit-chaos.html
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=201511 Ice volcanoes and other geology on Pluto
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20151105 New Horizons completes record-setting targetting manoeuvres
1. NASA/JHUAPL/SwRI
2. NASA/JHUAPL/SwRI
3. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute