Oxia Palus Quadrangle - Aram Chaos

Aram Chaos

Aram Chaos is an ancient impact crater near the Martian equator, close to Ares Vallis. About 280 kilometers (170 mi) across, Aram lies in a region called Margaritifer Terra, where many water-carved channels show that floods poured out of the highlands onto the northern lowlands ages ago. The Thermal Emission Imaging System (THEMIS) on the Mars Odyssey orbiter found gray crystalline hematite on the floor of Aram. Hematite is an iron-oxide mineral that can precipitate when ground water circulates through iron-rich rocks, whether at normal temperatures or in hot springs. The floor of Aram contains huge blocks of collapsed, or chaotic, terrain that formed when water or ice was catastrophically removed. Elsewhere on Mars, the release of groundwater produced massive floods that eroded the large channels seen in Ares Vallis and similar outflow valleys. In Aram Chaos, however, the released water stayed mostly within the crater's ramparts, eroding only a small, shallow outlet channel in the eastern wall. Several minerals including hematite, sulfate minerals, and water-altered silicates in Aram suggests that a lake probably once existed within the crater. Because forming hematite requires liquid water, which could not long exist without a thick atmosphere, Mars must have had a much thicker atmosphere at some time in the past, when the hematite was formed.

• Erosion in Aram Chaos, as seen by THEMIS.

• Blocks in Aram showing possible source of water, as seen by THEMIS.