NASA has published a comparative analysis of the spectral measurements of three moons of the dwarf planet Pluto which prove that in particular Nyx but also Hydra have a surface covered in water ice. The New Horizons space probe’s LEISA instrument carried out the measurements during the July 14, 2015 flyby. Unfortunately the location of the other two small moons, Styx and Kerberos in those hours didn’t allow spectral measurements.