Schematic of the Pluto system

The new HST/ACS observations made on March 2nd reveal that all three of Pluto's satellites are neutrally colored, unlike reddish Pluto itself. Pluto's reddish colour is believed to be due to reddening agents created by the effects of sunlight acting on its nitrogen and methane surface ices. Charon's surface is known to consist primarily of water ice; the similar colour of P1 and P2 may indicate they too have water ice surfaces. The colour similarity of Pluto's two small satellites to one another and to Charon is consistent with their all having been born as a result of a single giant impact, as previously indicated by their orbits and Charon's large mass.