Eight dice-sized bits of ice vanished within 4 days from a trench dug on Mars by the robotic arm on NASA's Phoenix lander, confirming what scientists suspected the material was. “It must be ice,” said mission principal investigator Peter Smith of the University of Arizona, Tucson. “These little clumps completely disappearing over the course of a few days: that is perfect evidence that it's ice. There had been some question whether the bright material was salt. Salt can't do that,” he said.