Free Astronomy Magazine September-October 2015

SEPTEMBER-OCTOBER 2015 es, probably of the cryovolca- nic type − an hy- pothesis sup- ported for long time by Alan Stern, principal investigator of the New Hori- zons mission. But let’s get back to the high-reso- lution images of the planet's surface taken by LORRI du- ring the flyby. Among the features that most attracted the researchers’ attention there are some flat plains extending to- wards the left lobe of the “heart” (infor- mally named “Tombaugh Regio”, after Clyde Tombaugh who discovered Pluto in 1930), which appear fractionated into ir- regular polygons (similar to those already observed in the opposite hemisphere, but in reduced scale), which are on average a few tens of kilometres across. These poly- gons are bor- dered by nar- row and deep troughs, some of which host- ing darker de- bris and in some cases real clusters of hills that seem to rise above the same poly- gons. The ini- tial working hypotheses on how these polygons may have formed are that they are either the result of the contraction of icy surface materials (like when mud dries), or the product of convective motions within a layer of surface ice rich in carbon mono- xide, methane and nitrogen, which due to its composition remains relatively fluid even at a temperature of minus 234 degrees C, measured at the surface. In the first days following the flyby were also made avail- able good images in false colour of the sa- A bove, a pro- visional map of Charon. Left, the satellite sys- tem of Pluto pho- tographed by New Horizons on 26 June, from 21.5 million km away. Next page, the best available images of Nix and Hydra. [NA- SA/Johns Hopkins University Applied Physics Labora- tory/Southwest Research Institute]