Spiral Troughs on Mars

Onset and migration of spiral troughs on Mars revealed by orbital
radar pp450-453
A pinwheel array of deep troughs has been one of the most perplexing
features of the north polar layered deposits on Mars. Many ideas have
been put forward about how it formed, but there is as yet no
consensus. Here, penetrating radar has been used to rule out
erosional cutting as a mechanism for the formation of the array.
Instead, it is concluded that the troughs are largely depositional
in origin, and have migrated to the poles and upwards in elevation
over the past two million years or so.
Isaac B. Smith and John W. Holt
doi:10.1038/nature09049