Valley networks have been recognized on Mars since the earliest NASA missions to the ‘Red’ planet. From Mariner and Viking mission images, ‘classic’ valley networks are typically negative relief, branching features that are a few kilometers wide, more than 100 meters deep, and up to 200 kilometers long. Recent studies using higher resolution orbital images returned from missions beginning with Mars Global Surveyor have now recognized a range of preservation states for valley networks, most of which are at a much finer scale than classic valley networks. These include sinuous ridges formed by landscape inversion where former negative relief fluvial pathways (often termed ‘inverted channels’) are now in positive relief as exhumed features.
New geomorphologic mapping and documentation of both ‘classic’ valley networks and other preserved morphological types in the Greater Meridiani Planum (GMP) region of Mars expands our understanding of where and when past surface aqueous conditions existed on the planet. Results from the mapping show that the majority of preserved valley networks (approximately 67 percent) are associated with the lowest stratigraphic units in the GMP region and, more specifically, in ancient cratered terrain. Three regional exposures of this terrain are apparent with each having valley network characteristics that differ from one another (see image). Based on the stratigraphy of geologic units, unit ages derived from previous studies, morphologic characteristics of valley networks, and potential terrestrial analogs for the mapped features, the events in the GMP region are consistent with episodic aqueous activity rather than a monotonic decline in climatic conditions with the transition from the Noachian to Hesperian period.
The full publication for this work is available as an open access Journal of Maps article at: https://www.tandfonline.com/doi/full/10.1080/17445647.2018.1530154
