NASA Cassini Image: Saturn's north polar hexagon

Saturn's north polar hexagon basks in the Sun's light now that spring has come to the northern hemisphere. 

Many smaller storms dot the north polar region and Saturn's signature rings, which appear to disappear into Saturn's shadow, put in an appearance in the background.

The image was taken with the Cassini spacecraft's wide-angle camera on Nov. 27, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 750 nanometers.

The view was acquired at a distance of approximately 403,000 miles (649,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 21 degrees. 

Image scale is 22 miles (35 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute

ESA Mars Express: North polar regions in transition

This image was acquired by the Mars Express High-Resolution Stereo Camera on 17 May 2010 and shows a part of the northern polar region of Mars at the northern hemisphere summer solstice.

The polar ice deposits follow the seasonal cycles. Studies made by Mars Express’s OMEGA instrument shows that the cap is covered by frozen water and carbon dioxide ice in winter and spring but by this point in the martian year all of the carbon dioxide ice has warmed and evaporated into the planet’s atmosphere.

Only water ice is left behind, which shows up as bright white areas in this picture. From these layers, large bursts of water vapour are occasionally released into the atmosphere.

In winter, part of the atmosphere recondenses as frost and snow on the northern cap. These seasonal deposits can extend as far south as 45°N latitude and be up to a metre thick.

Another phenomenon occurs on the curved scarps of the northern polar cap, such as the Rupes Tenuis slope (on the left of this image). During spring, the seasonal carbon dioxide layer is covered by water frost. At certain times, winds remove the the millimetre-thick top layer of frozen water, revealing the carbon dioxide ice below.

These processes bear witness to a dynamic water cycle on Mars and may lead to the varying accumulation of water ice over the polar cap.

 Chasma Boreale (box 1) is about 2 km deep, 580 km long and about 100 km wide. Its walls allow a perfect view into the strata within the deposits.

On the canyon floor impact craters are visible, some heavily covered by sand and some partly exhumed. Dark and light-toned deposits (box 2) deposits can be seen in a fine and regular covering.

The darker sediments have been dropped by the winds during spring dust storms. The patterns are created when the deposits change in quantity according to the seasons.

The northern polar ice cap is surrounded by a large dune field (box 3), parts of which extend 600 km to the south.

Credits: ESA/DLR/FU Berlin (G. Neukum)

NASA - North Polar Layers of Mars

Credit: NASA/JPL/University of Arizona

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.