The north polar layered deposits are layers of dusty ice up to 2 miles thick and approximately 620 miles in diameter. We can see the layers exposed on the walls of troughs and scarps cut into the deposits, such as the trough wall imaged here. The bright region at the top is the flat surface above the trough wall; it is higher than the terrain underneath.

The wall exposing these layers has a vertical relief of about 1970 feet. It is thought that the north polar layered deposits likely formed recently (i.e., millions of years ago) as rhythmic variations in Mars’ orbit changed the distribution of water ice around the planet. As ice moved to and from the polar region in response to a changing climate, layers of ice and dust built up at the poles.

By studying the history of these deposits, we hope to understand how the Martian climate has changed, similar to how scientists on Earth study ice cores from the North and South Poles. Three things are immediately apparent about the layers exposed on this trough face.

First, individual layers have different surface textures, which some scientists believe could reflect changing physical properties (such as dust content or ice grain size) of the underlying layer. Second, there are several unconformities, or places where one layer is interrupted and overlain by another layer.

These unconformities are due to periods where layers were eroded or removed, followed by times when new layers were deposited. Mapping the locations of unconformities can tell us how the deposit shrank and grew over time, and tell us where large changes in climate occurred, causing water ice to be removed from the polar regions.

Finally, the dark and bright streaks are due to recent winds blowing surface frost around, and can tell us about wind patterns in the current polar climate. This was imaged by the HiRISE camera onboard the Mars Reconnaissance Orbiter. HiRISE is the most powerful camera of its kind ever sent to another planet. Its high resolution allows us to see Mars like never before and could help other missions choose a safe spot to land for future exploration. Credit: NASA/JPL/University of Arizona

This image shows the west-facing side of an impact crater in the mid-latitudes of Mars’ northern hemisphere. Like many mid-latitude Martian craters, this one has gullies along its walls that are composed of alcoves, channels and debris aprons. The origins of these gullies have been the subject of much debate; they could have been formed by flowing water, liquid carbon dioxide or dry granular flows.

Many of the other features observed in and around this crater are indicative of an ice-rich terrain, which may lend credence to the water formation hypothesis for these gullies. The most notable of these features is scalloped terrain in and around the crater. This type of terrain has been interpreted as a sign of surface caving, perhaps due to sublimation of underlying ice. Sublimation is the process of a solid changing directly to a gas.

Another sign of ice is the presence of parallel lines and pitted material on the crater floor. Parallel linear cracks are also observed along the crater wall over the gullies, which could be due to thermal contraction of ice-rich material. together, these features are evidence for ice-rich material having been deposited in this region during different climatic conditions, material that has subsequently begun to melt and/or sublimate under current conditions.

More recently, wind-blown deposits have accumulated around the crater, as evidenced by the parallel ridges dominating the landscape. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter took the image on April 13, 2010. Image Credit: NASA/JPL-Caltech/University of Arizona

This just in from the Red Planet: Mars rover Opportunity has set a longevity record as it attempts a marathon trek across dangerous terrain; meanwhile, Spirit is in peril from the advancing Martian winter.

Despite their troubles, both rovers remain in the hunt for new discoveries. Details are provided in today's story from Science@NASA.