Post by Dr. Mariam Sowe
The High Resolution Stereo Camera (HRSC) on board the Mars Express has a large swath and high resolution [Jaumann et al. 2007]. This enables the capture of large geomorphic features while retaining the ability to track small-scale features over long distances. The HRSC has observed all of the giant outflow channels on Mars. They are supposed to be eroded fluvially as a consequence of the catastrophic release of water [Baker et al., 1992]. Most of them emanate from chaotic terrain [Sharp, 1973], which is heavily collapsed terrain and assumed as their source region. Outflow channels give insight to a different Martian climate with respect to hydrological conditions that apparently were different in the Late Hesperian or Amazonian, when they were formed [Tanaka, 1986].
Mangala Vallis is a huge outflow channel (400 km across in Image 1) located west of the Tharsis bulge. Crater counts indicate an age of about 3.6 Ga for the ancient surrounding highlands, 1.4 Ga for the main valley floor, and 450 Ma for some younger and smaller tributaries [Werner, 2006]. Valley networks indicate the flow of liquid water across the Martian surface. The streamlined surface features are the result of erosion by liquid water or ice. Eroded craters with teardrop-shaped tails, scour marks, and streamlined islands are common flow features of outflow channels [Rodriguez et al., 2005].
Kasei Vallis is proposed to have formed by the erosion of liquid water or glaciers. It is the largest outflow channel on Mars. Lava flows (corresponding to bluish surface in Image 2) cover its floor, obscuring previous traces of fluvial landforms.
Baker, V.R., M.H. Carr, V.C. Gulick, C.R. Williams, and M.S. Marley (1992): Channels and valley networks, Mars, pp. 493-522. [Abstract]
Jaumann, R., G. Neukum, T. Behnke, T.C. Duxbury, K. Eichentopf, J. Flohrer, S.V. Gasselt, B. Giese, K. Gwinner, E. Hauber, H. Hoffmann, A. Hoffmeister, U. Köhler, K.D. Matz, T.B. McCord, V. Mertens, J. Oberst, R. Pischel, D. Reiss, E. Ress, T. Roatsch, P. Saiger, F. Scholten, G. Schwarz, K. Stephan, M. Wählisch, and t.H.C.-I. Team (2007): The high-resolution stereo camera (HRSC) experiment on Mars Express: Instrument aspects and experiment conduct from interplanetary cruise through the nominal mission, Planetary and Space Science 55, pp. 928-952. [Abstract]
Rodriguez, J.A.P., S. Sasaki, R.O. Kuzmin, J.M. Dohm, K.L. Tanaka, H. Miyamoto, K. Kurita, G. Komatsu, A.G. Fairnén, and J.C. Ferris (2005): Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars, Icarus 175, pp. 36-57. [Abstract]
Sharp, R.P. (1973): Mars: fretted and chaotic terrains, JGR 78, pp. 4073-4083. [Abstract]
Tanaka, K.L. (1986): The stratigraphy of Mars, Journal of Geophysical Research 91, p. 139. [Abstract]
Werner, S. (2006): Major Aspects of the Chronostratigraphy and Geologic Evolutionary History of Mars, PhD thesis, Freie Universität Berlin, Berlin, 160 pp. [Abstract]