Light-toned paleo-surface Long/lat: E, 23.76N Rational: During the deposition of the layered unit, a layer may have remained at the surface for a longer time than the rest of the sequence, and recorded many impacts. This cratered surface was later covered by subsequent layers. This particular layer has recorded different depositional conditions than the rest of the clay unit. Morphology & mineralogy: This Fe/Mg- smectite rich, light-toned, strongly indurated paleo-surface is exhumed in two nearby outcrops, south of the landing ellipse. Many brighter, almost-circular, sometime layered features are spread over the surface. This surface interpreted as a paleo-surface is different from the dark paleo-surface in the flank of Mawrth Vallis through its higher albedo. The size of the almost-circular features is also smaller here. MSL tasks: At large scale, study the relation of the paleosurface to upper and lower layers, the circular features, its fracturation. At small scale, the grain structure, the mineralogy and chemistry of the rocks, in the circular features and in between. HRSC mosaic with HRSC nadir & color images Next slide

1 km CTX & HiRISE mosaic with HiRISE color images

CTX & HiRISE mosaic with THEMIS thermal inertia (Fergason, R. L.) Next slide The paleo-surface has a strong thermal inertia. 1 km After next slide J m -2 K -1 s -1/2

200 m HiRISE mosaic Almost-circular features are visible on most of the surface through its lighter ton (the largest are indicated by white arrows), with sizes from ~50 m to ~10 m.

200 m HiRISE mosaic