The Nasa Mars lander Phoenix is possibly sitting directly on an ice patch.
A photo of the ground underneath the Phoenix Mars Lander shows a harder substrate that may be ice exposed by the thrusters.

"This suggests we have an ice table under a thin layer of loose soil," said the lead scientist for the Robotic Arm Camera, Horst Uwe Keller of Max Planck Institute for Solar System Research, Katlenburg- Lindau, Germany. Maybe NASA should have Phoenix look at it's back, there might be a bunch of Martians standing there.
More details on the NASA site. More Phoenix coverage.