The Mars Reconnaissance Orbiter using the SHARAD radar (side view)
This artist's concept of the Mars Reconnaissance Orbiter highlights the spacecraft's radar capability. The SHARAD instrument is the long pole-like feature that extends horizontally from the spacecraft. The radar is pictured "beaming" down under the surface of Mars. The foreground of the image is a cross section of the planet, showing the crust, the layers below and, ultimately, reservoirs of ice or liquid water.
The SHARAD instrument will look into the first few hundreds of feet below the martian surface, up to 1 kilometer.