Erasure of First-order Tributaries via Climate Change: Lessons for Mars from Earth

Introduction: Since Mariner 9 first imaged fluvial channels on the surface of Mars thirty years ago, one of the continuing problems of its hydrologic history has been the apparent absence of small, first-order tributaries to the large outflow channels and the larger integrated channels of the highlands [1]. Drawing on terrestrial examples from the northeast Sahara, where Quaternary climate has cycled between a savannah and hyperarid environment, the Mars-analogous landscape has been used in the past to promote the efficiency of aeolian processes [2-4] and the fluvial processes of sapping and headwall erosion [5,6]. Following up on the work of Haynes [7] more recent work on the landscape of the Sahara has emphasized the role of climate change in sculpting surface features [8]. Although we have yet to determine whether climate change on Mars was monotonic or cyclic during the late Noachian/early Hesperian, the processes may have the same end product. Discussed here are the processes of tributary obscuration based on terrestrial examples of aeolian infilling, landscape lowering and stabilization by development of a lag surface, and planation due to sand sheet formation and bedrock erosion.