At www.sciencedaily.com/releases/2010/08/100827082326.htm …. Orcus Patera is a mysterious elliptical depression near the equator of Mars, some 380km by 140km in a NNE – SSW direction. It has a rim that rises up 1800m above the surrounding plain while the floor of the depression is some 400 to 600m below the surrounding landscape. It doesn’t fit into any currently accepted pattern – impact or volcanic
