-- Pluto's moon Kerberos played quite a trick on scientists.
Prior to the New Horizons flyby, scientists tried to weigh the faint moon by measuring its gravitational influence on neighboring moons and found it was strong. The findings led scientists to suspect Kerberos could potentially be massive and theorized its faint appearance was because the moon was covered in dark material.
The moon's surface is also highly reflective, just like Pluto's other small moons, indicating it is likely covered by a sheet of clean water ice, NASA said.
"Our predictions were nearly spot-on for the other small moons, but not for Kerberos," New Horizons co-investigator Mark Showalter said in a statement. Scientists will now use the results to gain a better understanding of the satellite system around Pluto.