The central portion of the Osuga Valles on Mars.
The central portion of the Osuga Valles on Mars.
--Image: European Space Agency
The valleys carved into the surface of Mars, so familiar looking, were carved by rainfall, a recent study finds.

     Twisting structures on the red planet long have intrigued scientists who noticed the resemblance to Earthen riverbeds. That likeness led to supposition that there was once enough water on Mars to feed streams.
     This is more than academic speculation. The how and why of these swirls in the Martian soil tell the story of the planet’s climatic history and past habitability. Unlike other planets in the solar system, Mars underwent a transition from being more habitable in the distant past to less habitable today.
     For there to be river runoff erosion, the climate on Mars would have been different. “Frequent precipitation and an active hydrological cycle are necessary to support a significant amount of overland flow, with temperatures at least episodically rising sufficiently to allow liquid water to exist," authors note in the study published in Science Advances. This implies that "a thicker CO2 (carbon dioxide) atmosphere is a necessary factor.”
     Using statistics gathered from spacecraft exploring Mars, researchers examined mapped river valleys and concluded that the contours were created by the runoff of rainwater.
     “Mars once had an active hydrologic cycle,” the authors say, and "Mars’ valley networks were formed primarily by overland flow erosion, with groundwater seepage playing only a minor role.”
      The Science Advances study, published online, is, Branching geometry of valley networks on Mars and Earth and its implications for early Martian climate,” by Hansjoerg J. Seybold, ETH Zurich, Switzerland, et al.  Find more information on the website for the public university, ETH Zurich, Switzerland.


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