Updated global map of Martian valley networks and implications for climate and hydrologic processes

Abstract

[1] Martian valley networks have long been viewed as some of the best evidence of prolonged surface water on Mars. Analysis from Viking data showed that valleys were primarily contained on the ancient crust, drainage networks were immature, and large undissected regions occurred in between individual systems. These observations led many to propose that they formed primarily by groundwater processes, and limited or no climate change from the present state was required. Using more recent and higherresolution data sets, including visible, infrared, and topographic data, we have manually remapped valleys on a global scale. More than eight times as many valleys have been identified on the surface, and calculated drainage densities are, on average, higher by a factor of 2. Further, regions previously thought to be undissected have significant incision by fluvial processes. Most of these systems seem to have formed around the NoachianHesperian boundary (∼3.8-3.6 Ga). Minor valley formation continued through the Hesperian and into the Early Amazonian epoch, approximately 2.8 Ga ago. The new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels, terraces, multiple periods of formation, complex network morphology, and correlation with other fluviosedimentary features and chloride salts on Mars. Groundwater processes or a transient steam atmosphere generated by impacts played, at most, a minor role. These new results imply that Mars had a long-lived period or periods of clement conditions toward the end of the Noachian epoch that supported a hydrologic cycle and potentially a biosphere.

Global drainage patterns and the origins of topographic relief on Earth, Mars, and Titan

“…We relied on a global database of Martian river networks (18). Sinks were identified as the topographically lowest extremities within each network; the validity of these sinks was spotchecked visually.…”

Sedimentology and climatic environment of alluvial fans in the martian Saheki crater and a comparison with terrestrial fans in the Atacama Desert

“…Martian alluvial fans have been identified ranging in scale from sub-kilometer (Williams and Malin, 2008) to a few kilometers (Burr et al, 2009) to tens of kilometers Kraal et al, 2008;Anderson and Bell, 2010;Wilson, 2011, 2012). The well-preserved, mid-latitude fans of the Hesperian (and perhaps even younger) (Grant and Wilson, 2011;Kraal et al, 2008;Moore and Howard, 2005;Morgan et al, 2012a,b) are of particular interest because they, along with deltas (e.g., Malin and Edgett, 2003;Moore et al, 2003;Lewis and Aharonson, 2006;Pondrelli et al, 2008Pondrelli et al, ,2011Mangold et al, 2012b;Wilson et al, 2013) and small valleys in the mid-latitude regions (e.g., Hynek et al, 2010;Fassett et al, 2010;Howard and Moore, 2011;Mangold, 2012), may represent a widespread episode of large-scale fluvial landform construction and modification on Mars occurring well after the Late Noachian to Early Hesperian epoch of valley network incision (Grant and Wilson, 2011;Howard and Moore, 2011). This later period of fluvial activity occurred in an environment thought to be characterized by a relatively thin atmosphere and global cryosphere (Carr and Head, 2010;Fassett and Head, 2011;Lasue et al, 2013).…”

Quantifying geological processes on Mars—Results of the high resolution stereo camera (HRSC) on Mars express

“…and Howard, 2002;Howard et al, 2005;Ansan and Mangold, 2006;Ansan et al, 2008;Mangold et al, 2008b;Hynek et al, 2010;Ansan and Mangold, 2013). Only few of dense branching valley networks retained inner channels, because of subsequent dust/ sand filling (e.g., Irwin et al, 2005a;Jaumann et al, 2005;Kleinhans, 2005).…”