Layers Exposed at Polar Canyon This false-color subframe of an
image from the High Resolution Imaging Science Experiment camera
on NASA's Mars Reconnaissance Orbiter shows the north polar
layered deposits at top and darker materials at bottom, exposed
in a scarp at the head of Chasma Boreale, a large canyon eroded
into the layered deposits. The polar layered deposits appear red
because of dust mixed within them, but are ice-rich as indicated
by previous observations. Water ice in the layered deposits is
probably responsible for the pattern of fractures seen near the
top of the scarp. The darker material below the layered deposits
may have been deposited as sand dunes, as indicated by the
crossbedding (truncation of curved lines) seen near the middle
of the scarp. It appears that brighter, ice-rich layers were
deposited between the dark dunes in places. Exposures such as
these are useful in understanding recent climate variations that
are likely recorded in the polar layered deposits. NASA's Jet
Propulsion Lab