resonance. A hypothesis explaining such a near-resonance is that the resonances originated before the outward migration of Charon following the formation of all five known moons, and is maintained by the periodic local fluctuation of 9 percent in the Pluto–Charon gravitational field strength. Exploration The New Horizons spacecraft visited the Pluto system and photographed Pluto and its moons during its flyby on 14 July 2015. Of Pluto's smaller moons, only Nix and Hydra were imaged at resolutions high enough for surface features to be visible. Prior to the flyby of the Pluto system, measurements of Nix's size were performed by the Long Range Reconnaissance Imager on board New Horizons, initially estimating Nix to be about in diameter. The first detailed images of Nix taken by New Horizons from a distance of about were downlinked, or received from the spacecraft on 18 July 2015 and released to the public on 21 July 2015. With an image resolution per pixel, Nix's shape was often referred to as a "jelly bean" shape. Enhanced color images from the Ralph MVIC instrument of New Horizons show a reddish region on its surface. From those images, another accurate measurement of Nix's dimensions was made, giving the approximate dimensions of . Notes References External links Background Information Regarding Our Two Newly Discovered Satellites of Pluto – The discoverers' website NASA's Hubble Reveals Possible New Moons Around Pluto – Hubble press release Nix In Depth – NASA Solar System Exploration Moons of Pluto 20050615 Nyx Moons with a prograde orbit