Cataracts on Mars
In a paper published in the journal Geology Nicholas Warner and Sanjeev Gupta from ESE, together with coworkers at UCL, present evidence for erosional retreat of a giant cataract in a martian outflow channels.
The history of water on Mars is crucial to understand in evaluating whether life existed or still exists on the planet. In a paper published in the journal Geology Nicholas Warner and Sanjeev Gupta from ESE, together with coworkers at University College London, present evidence for erosional retreat of a giant cataract in a martian outflow channel. The research shows that not only have fluvial erosional processes operated in Mars' past, but also that the outflow channels are shaped by infrequent episodic flood events.
The research focused on a cataract within a 600m deep tributary channel of Ares Vallis, a major outflow channel and the landing site of the NASA Pathfinder mission. Although the existence of outflow channels on Mars has been known since the Viking mission, the nature of the erosion that produced them has remained controversial. Whether the outflow channels are produced by a small number of energetic flood events or regular episodic outflows of water has important implications for the occurrence of bodies of water on the surface of the red planet that may have provided habitats for living organisms.
Within the tributary channel Walker and Gupta studied a 300m high cataract, a crenulated region of the channel with higher angle. On Earth either water falls or rapids are sometimes termed cataracts. Within the martian channel the cataract would have been a turbulent series of rapids during flooding. The research examined the age of the channel floor by counting the numbers of craters of different sizes, which allows the age of the surface to be estimated. The crater counting suggested that their were two major periods of erosion at 3.7 Ga, during the late Noachian-early Hesperian epoch of Mars, and 2.7 Ga, during the early Amazonian.
Warner and Gupta's results also suggest that erosion within the tributary occurred by retreat of the cataract up-stream. On Earth cataracts usually initiate breaks in slope. In this case this was where the tributary entered the Ares Vallis.
The study shows that analysis of topographic features, together with the dating of surfaces by crater counting and comparisons to landforms on Earth can allow the history of water on Mars to be traced.
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