This bizarre terrain covers the entire floor of the basin. The deposits are several kilometers thick. Methods of deposition, methods of erosion are not fully understood.

It has been pointed out repeatedly in this forum that despite the relatively high atmospheric pressure, frequent cloud cover and periods of relative warmth in the Hellas Basin, it is and has long been a sere desert.

Standard interpretation is that Hellas is the largest impact crater on Mars, and possibly the largest in the Solar System, and it is generally considered to be extremely ancient. But what if it isn't an impact structure at all, or is only partially due to impact?

Could something else have created the Hellas Basin?

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As for the dunal "rills" --

1. Are these dunes composed of black sand?

2. If not, what could they be??

3. Can water migrate from subsurface reservoirs through the dunes to the surface? Would it?

4. What other volatiles might be available to cause these "rills?"

5. Or could they be caused by solid or viscous materials rolling down the face of the dunes?

I'm sure there are other questions we could raise...

Cheers, BRFelix