Today's Image of Mars was taken by HiRISE and shows part of an impact crater in Terra Cimmeria that is completely cast in shadow. Terra Cimmeria is located in the southern highland region of Mars.
Much of the crater floor is cast in deep shadow because the sun was only 11 degrees over the horizon. The HiRISE cameras aboard the Mars Reconnaissance Orbiter are sensitive enough that they can see within most shadows. The image below shows an area completely shrouded in shadow, but HiRISE can still see features indicative of ice flow, a common finding in the southern highlands.
Clicking on this image will take you to the original image from HiRISE. [See their caption]