The upper image is a radargram from the Mars Advanced Radar for Subsurface
and Ionospheric Sounding (MARSIS), showing data from the subsurface of
Mars in the layered deposits that surround the north pole. The lower image
shows the position of the ground track on a topographic map of the area
based on Mars Orbiter Laser Altimeter data. The images are 458 kilometers
(285 miles) wide.
The MARSIS echo trace splits into two traces to the right of center, at
the point where the ground track crosses from the smooth plains onto the
elevated layered deposits on the right. The upper trace is the echo from
the surface of the deposits, while the lower trace is interpreted to be
the boundary between the lower surface of the deposits and the underlying
material. The strength of the lower echo suggests that the intervening
material is nearly pure water ice. The time delay between the two echoes
reaches a maximum of 21 microseconds at the right of the image,
corresponding to a thickness of 1.8 kilometer (1.1 mile) of ice. The total
elevation difference shown in the topographic map is about 2 kilometers
(1.2 mile) between the lowest surface (magenta) and the highest (orange).
MARSIS is an instrument on the European Space Agency's Mars Express
orbiter. NASA and the Italian Space Agency jointly funded the instrument.
The Mars Orbiter Laser Altimeter is an instrument on NASA's Mars Global
Surveyor orbiter.
