www.jpl.nasa.gov/news/2010-180 data from NASAs Mars Reconnaissance Orbiter have provided evidence of a large chasm and a series of spiral troughs on the northern ice cap of Mars (see also Nature May 27th and NASA newsletter May 26th at info [at] jpl [dot] nasa [dot] gov ). The Shallow Radar instrument onboard is sending back detailed information and it seems the northern ice cap is a stack of ice and dust layers up to 2 miles deep covering an area roughly the size of Texas. The radar data is analysed on a computer and scientists can peel back the layers like an onion.
Another feature of the ice cap is a canyon as long as the Grand Canyon on earth but wider and deeper. There are also troughs that spiral outward from the centre like a gian pinwheel. It is not known how they formed.