RE-EXAMINATION OF THE WARREGO VALLES CHANNELS ON MARS: IMPLICATIONS FOR THE EARLY 'WARM-WET' CLIMATE PARADIGM

摘要

Since its discovery by the Viking Orbiters in the 70's, Warrego Vallis has often been cited as definitive evidence linking the early environment of Mars to being "warm and wet". Indeed, its Noachian age (> 3.5 Ga) and dendritic-like morphology satisfying Horton laws have been proposed to indicate precipitation of liquid water and runoff across a drainage basin. However, detailed analyses using the Thermal Emission Imaging System, and the Mars Orbiter Laser Altimeter reveal morphological characteristics inconsistent with a mature system formed by liquid water precipitation. Specifically, the channel head morphology does not display characteristics expected of terrestrial dendritic networks, faults and crater rims are identified as the source of most channels, widths of individual channels do not increase downstream the way they do on Earth, and terrestrial perennial-channel slope-area scaling relationships are not observed, although Hack's law is satisfied. Channels can be traced upstream to an origin at the base of faults or crater rims, where they start "fully formed", pointing to a subsurface, point-source origin of the fluid that carved the channels. We argue that the additional considerations outlined above are more consistent with subsurface sources of water decoupled from the atmosphere, rather than from meteoritic water fed by precipitation from an active hydrological cycle.