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Aonia Terra - Colorful Mars

Aonia Terra is an upland region in the southern highlands of Mars and known for massive cratering like the 200 km large and famous Lowell crater (see overview map) just 130 km southwest of the crater shown in the center of the image. The 30 km wide unnamed impact crater is embedded in a surprisingly colorful landscape of large channel networks. These valleys are interpreted as an indication for precipitation of liquid water along with groundwater activity. The channels were active in the Late Noachian and Early Hesperian epochs of Mars. Interestingly, the valleys appear to be partly filled with a dark colored material and the relief seems to be inverted in some few points. This inversion of relief can occur when the materials filling the valley floor are, or become, more resistant to erosion than the adjacent surface. This may happen by channel bed sediment induration through geochemical cementation under the presence of water, or by armoring of the channel bed with erosion resistant, often coarse-grained sediments. Another possibility is a later infill of the valleys with lava in volcanic regions.

The surface around the impact crater likely consists of different materials. South of the crater (left side of the image), the surface displays a warm red color, changing towards a darker brown/grayish tone closer to the crater. In this region, many small buttes can be found. Then, the surface appears fairly smoothened, this becomes well visible at the crater rims and further to the north (right side of the image). Here the coloration of the surface changes towards a lighter tone, and the rims of the channels appear less defined. Finally, at the right side of the image, the surface looks much smoother. These many colors hint a surprising variability of the surface mineralogy in this region.

Inside the impact crater, a beautiful dark dune field can be spotted measuring just 5.4 x 2.7 km, resting on a light-toned, bright deposit. At closer inspection, many little buttes and knobs can also be found inside the crater, showing that the crater is filled with different materials that accumulated inside. Measurements from the THEMIS instrument on board of NASA’s Mars Odyssey spacecraft document a very high thermal inertia in these deposits confirming the wide difference in composition.