From Wytse Sikkema, Shell Deepwater Services
The news piece about asteroid impacts on Mars perpetuates the myth that only water could have produced the channel-like features we see on the surface of the planet (14 December 2002, p 22, and p 15, this issue).
These channels have clearly been scoured by a flowing medium, but this does not have to be water. A very likely alternative is turbidity currents. These occur when a volume of a medium such as air or water is heavier than the surrounding medium because of suspended particles. Examples on Earth include avalanches, volcanic ash flows, and, in the deep oceans, turbidity currents – flows of suspended sediment.
Detailed images of ocean floor channels are much more similar to the pictures of Mars than any river system. Mars has all the requirements for turbidity currents. Billions of years of meteorite bombardment have produced thick layers of fine dust. The well-documented dust storms and dust devils move this dust to higher areas, where it can become suspended in the atmosphere and flow downhill as a turbidity current, eroding into the soft surface to create the meandering channels.
The absence of water on Mars will help this process, because the fine dust will not be stabilised by ground water, as happens on Earth. Another factor may be Mars’s low gravity, which slows the settling out of suspended dust particles.
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Thus the formation of channels is an ongoing process, which explains why the channels are usually younger than the surrounding craters. It also explains the “ocean-like” appearance of the lowest parts of Mars: they have been filled in by the dust from turbidity currents.
The turbidity-current idea has the advantage that it only involves known sedimentation processes and does not require difficult, far-fetched theories about large amounts of water once being present on Mars. Such theories are too much driven by the wish that there once was water on Mars, and hence, possible life there.
Houston, Texas, US
