... Moon . ... Cassini on a mystery's trail . Scientists will use NASA's Cassini spacecraft to investigate vaporized water ice movement on Saturn's moon Iapetus. ... Also shown here is the complicated transition region between the dark leading and bright trailing hemispheres. ... N ASA scientists are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre "runaway" process that is transporting vaporized water ice from the dark areas to the white areas of the Saturnian moon. ...