Annotated Version
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 ice-rich layered deposits that surround the south pole. The
lower image shows the position of the ground track (white line) on a
topographic map of the area based on Mars Orbiter Laser Altimeter data.
The images are 1,250 kilometers (775 miles) wide.
The MARSIS echo trace splits into two traces on the left side of the
image, at the point where the ground track crosses from the surrounding
plains onto the elevated layered deposits. 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. Near the image center, the
bright lower echo abruptly disappears for unknown reasons. The time delay
between the two echoes reaches a maximum of 42 microseconds left of
center, corresponding to a thickness of 3.5 kilometers (2.2 miles) of ice.
The total elevation difference shown in the topographic map is about 4
kilometers (2.5 miles) between the lowest surface (purple) and the highest
(red).
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 flew on NASA's Mars Global Surveyor
orbiter.
