Free Astronomy Magazine September-October 2015

9 SEPTEMBER-OCTOBER 2015 PLANETOLOGY et’s actual diameter, considered on more than one occasion smaller than that of another dwarf planet, Eris. New measure- ments indicate that Pluto has a diameter of 2,370 km, hence appreciably larger than tom was initially melted by the impact and then refrozen back into larger grains, less effective at reflecting sunlight. Another interesting structure clearly vis- ible on Charon is a dark region about 320 km across, located next to the north pole, whose origin is so far un- known. Thanks to the images of Plu- to’s disk taken by LORRI in the first half of July, plan- etary scien- tists were able to defi- nitely solve the o u t s t a n d i n g issue on the plan- A bove, 13 July, the best pic- ture of Charon’s globe, showing the details of a re- gion subsequent- ly photographed on 14 July from 79,000 km away. [NASA/ Johns Hopkins Univer- sity Applied Phy- sics Laboratory/ Southwest Re- search Institute] On the side, the New Horizons team’s jubilation for the images of Pluto arrived just before closest approach. [NASA/ Bill Ingalls]