Aram Chaos

Geology

Formation

Aram Chaos, as an impact crater, started its formation with the high velocity impact of an unknown smaller body on the surface of Mars. This formed the large, circular depression that originally made up the crater. This crater was then filled with sediments, likely carried by aeolian processes, that were deposited into Aram Chaos over time. Subsequently, and in tandem with the compilation of these sedimentary layers, and aquifer formed beneath the surface of the crater.

Chaotic Terrain and Aqueous Environment

Following the deposition of sedimentary layers and the formation of the subsurface aquifer, a catastrophic geologic event occurred which caused the release of the subsurface aquifer and the subsequent catastrophic flooding, creating chaotic terrain within Aram Chaos. The repetition of this process led to layered terrains within Aram Chaos, including layers of the mineral hematite. Several minerals in Aram Chaos, including the hematite sulfate minerals and water-altered silicates, suggest that a lake probably once existed within the crater at some point in time. Scientists also suggest that flood channels within Aram Chaos were carved within just weeks or months by catastrophic outflows of groundwater from beneath Aram Chaos and nearby regions. Because forming hematite requires liquid water, which cannot exist without a thick atmosphere, the presence of hematite also suggests that Mars had a much thicker atmosphere at some time in the past. Tilting and erosion of Aram Chaos is also evident in satellite imagery taken of the crater.

Possible Volcanic Constructs

There is a possible volcanic component to the formation of outflow channels in Aram Chaos. By melting the permafrost or ground ice originally in the crater, geothermal activity may have caused the creation of the visible outflow channels in the impact crater. High resolution MOC images of the chaotic terrains in Aram Chaos show possible volcanic features within the crater, including hills resembling volcanoes, possible magmatic intrusions within the older rock layers, and possible volcanic ash deposits on the crater floor.

Mineralogical Composition

Not including dust and regolith common on the surface of Mars, two distinct sections of identifiable minerals have been determined to exist within Aram Chaos: a mixture of hematite and/or goethite and a mixture of ferric oxides and sulfates. Specifically, these minerals can be seen as two layers in Aram Chaos, described from top to bottom. The first layer consists mostly of nanophase iron oxides, which is about 250–500 meters thick, while the second layer is made up of a less than 500 m layer of polyhydrated sulfate and hematite.

Ferric hydroxysulfate (Fe3+SO4OH) has been found in Aram Chaos. It was probably formed from the heating and oxidation of hydrated ferrous sulfates. The heat may have come from the deposition of lava or ash. Another psossibility is that heat came from the ground by way of hydrothermal processes. This iron and sulfur compound was discovered with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument.

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