Premise: Digging in a different trench Phoenix's robotic Arm connected with a hard surface that has scientists excited about the prospect of next uncovering an icy layer.  "We have dug a trench and uncovered a hard layer at the same depth as the ice layer in our other trench," said Washington University robotic arm investigator for Phoenix, Ray Arvidson. The arm tried at least three times to penetrate the layer, but was unsuccessful. As a result the arm went into a holding pattern, awaiting its next commands.
Hypothesis: You can find ice buried under the ground.