Stream orientations on Mars reveals how the planet has been distorted after water flowed

What is it about?

Water flows downhill. With this basic idea, we might look at other planets where fluids flowed on the surface in the past and see if the modern downslope direction is different from the downslope direction implied by the channels. This simple idea is hard to implement however. In networks of rivers on Earth, for example, orientation varies across them and depends on the scale at which you work out the downslope direction. In this study led by Ricci Bahia, >25,000 Martian channels and inverted channels were mapped out. Conformance to the regional slope depended on the length of the channel. Even allowing for scale, only 38% of valleys are conformable with their local slope direction (i.e., are within 20˚), the rest are discordant. Much of this is due to the immaturity of the erosion, but some large valleys are discordant, suggesting their orientations originate from other causes (e.g., planetary tectonics or palaeolake outburst floods - the outburst flooding of crater lakes).

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Why is it important?

These results suggest that discordance analysis could be useful in working out where channels were formed in particular settings. It may also be helpful in working out areas of the planet that have been strongly modified and hence are unsuitable for palaeohydraulic analysis.