NASA’s New Horizons probe has finally filled out its family portrait of Pluto and its moons – and Kerberos, the last moon to get its closeup, turns out to be nothing like what scientists expected.
Before the piano-sized spacecraft’s July flyby, an analysis of Kerberos’ gravitational influence on Pluto’s four other moons suggested that it had some heft. But the fact that it was so dim led the mission team to conclude it must have a dark surface. Otherwise, why would an object so large reflect so little light?
It turns out that Kerberos is almost as tiny as Pluto’s smallest moon, Styx. Like Styx, Kerberos’ surface appears to consist of relatively clean water ice, making it bright enough to reflect about half of the sunlight it receives.