It’s a complete Pluto family photo – or at least a photo of the family members we’ve already met.
For the first time, NASA’s New Horizons spacecraft has photographed Kerberos and Styx – the smallest and faintest of Pluto’s five known moons. Following the spacecraft’s detection of Pluto’s giant moon Charon in July 2013, and Pluto’s smaller moons Hydra and Nix in July 2014 and January 2015, respectively, New Horizons is now within sight of all the known members of the Pluto system.
“New Horizons is now on the threshold of discovery,” said mission science team member John Spencer, of the Southwest Research Institute in Boulder, Colorado. “If the spacecraft observes any additional moons as we get closer to Pluto, they will be worlds that no one has ever seen before.”
Drawing even closer to Pluto in mid-May, New Horizons will begin its first search for new moons or rings that might threaten the spacecraft on its passage through the Pluto system. The images of faint Styx and Kerberos shown here are allowing the search team to refine the techniques they will use to analyze those data, which will push the sensitivity limits even deeper.
Kerberos and Styx were discovered in 2011 and 2012, respectively, by New Horizons team members using the Hubble Space Telescope. Styx, circling Pluto every 20 days between the orbits of Charon and Nix, is likely just 4 to 13 miles (approximately 7 to 21 kilometers) in diameter, and Kerberos, orbiting between Nix and Hydra with a 32-day period, is just 6 to 20 miles (approximately 10 to 30 kilometers) in diameter. Each is 20 to 30 times fainter than Nix and Hydra.