Interannual Comparison of Water Vapor in the North Polar Region of Mars

The development of the south polar Chasma Australe re-entrant has been discussed for several years and a variety of theories including eolian, aquatic, subglacial and tectonic mechanisms have been proposed for its formation. Morphological observations and studies of recent imagery support the idea of successive headward erosion and removal of volatile–rich sub–surface material combined with collapse and eolian blow–out processes. Introduction: The south polar Chasma Australe is a prominent arcuate elongated trough. Discussed models are formation by eolian processes [2, 3], aqeuous carving [4, 5], subglacial volcanic processes [5, 6] as well as tectonically triggered catastrophic outflow events [1] and basal melting [13]. In this work we provide some aspects to contribute to the understanding of its development. We have mapped the circum–Chasma Australe region on the basis of available imagery (Viking, Global Surveyor MOC, Odyssey THEMIS) at all resolutions and performed morphometric measurements on the basis of Laser Altimetry topographic data (MOLA) to evaluate outflow models proposed for the Chasma Australe development. A detailed description of the general morphology of the Chasma Australe has been provided by [1]. Fig. 1: Map of geomorphologic units of the Chasma Australe region, Promethei Planum and adjacent units. The Chasma Australe system is accompanied by several unlabeled Chasmata (2-4) to the east and west. Several elliptical and circular shaped depressions are located near the heads of secondary (2) re–entrants which indicate identical formation processes. Earlier stages of development (3-4) are presented by small third generation re–entrants. Light material near the terminus of Chasma Australe is connected to impact ejecta, which might be rich in volatiles, as lobate ejecta blankets indicate as well. Lineations south of the head of Chasma Australe. Geomorphologic and geologic setting: The Chasma Australe is an arcuate and elongated steep sided depression with a length of ≈500 km and a width of 16.5 km at its head and 93 km at its terminus. The Chasma head begins near −82◦S/90◦E and reaches down to 71◦S/86◦E with an opening angle of ≈ 30◦. It terminates in the Promethei Planum, a large circum-polar basin. The head of Chasma Australe is a well–defined, almost circular depression at an elevation of 2500 m with a depth of 950 m. Inside the U–shaped depression a secondary almost circular depression with a depth of ≈100 m and a diameter of ≈5 km appears. The Chasma terminus is situated at an elevation of ≈1060 m and is marked by a lobate–shaped remnant of possible base rock material.