The radargram in the upper panel of this image composite shows the subsurface of a unit of the Medusae Fossae Formation. The Medusae Fossae are mysterious deposits that form hills in the northern lowlands of Mars as seen in the bottom image. The top image is a time delay rendering of the radar waves emitted by Mars Express' MARSIS sounder showing subsurface echoes reflected back to the spacecraft.
These echoes from the subsurface are correlated with the projection of the lowland plains beneath the Medusae Fossae Formation deposits. The electrical properties inferred from the data suggest these deposits may be ice-rich.