ESA Mars Express Image: Cappuccino swirls at Mars’ south pole

Swirls of chocolate, caramel and cream, this image is definitely one to trigger sweet-toothed cravings.

Smooth cream-coloured plateaus surrounded by cocoa-dusted ridges interspersed with caramel-hued streaks create a scene reminiscent of a cosmic cappuccino.

This picture is, perhaps surprisingly, from ESA’s Mars Express, which has been exploring and imaging the martian surface and atmosphere since 2003.

We may be used to seeing numerous images of red and brown-hued soil and ruddy landscapes peppered with craters, but the Red Planet isn’t always so red.

The bright white region of this image shows the icy cap that covers Mars’ south pole, composed of frozen water and carbon dioxide.

While it looks smooth in this image, at close quarters the cap is a layered mix of peaks, troughs and flat plains, and has been likened in appearance to swiss cheese.

The southern cap reaches some 3 km thick in places, and is around 350 km in diameter. This icy region is permanent; in the martian winter another, thinner ice cap forms over the top of it, stretching further out across the planet and disappearing again when the weather warms up.

The cap is around 150 km north of Mars’ geographical south pole and Mars Express has shed light on why this ice cap is displaced.

Perspective view of Hellespontus Montes

Credit: ESA

Deep impact craters,notably the Hellas Basin, the largest impact structure on the entire planet at 7 km deep and 2300 km across, funnel the strong winds that blow across Mars towards its southern pole, creating a mix of different low- and high-pressure systems.

The carbon dioxide in the polar cap sublimates at different rates in these regions with contrasting pressure, resulting in the cap’s lopsided structure.

Mars Express imaged this area of Mars on 17 December 2012, in infrared, green and blue light, using its High Resolution Stereo Camera.

This image was processed by Bill Dunford, using data available from the ESA Planetary Science Archive.

ESA's Mars Express: Hellas basin - deep down

Credit: ESA/DLR/FU Berlin

Scarring the southern highlands of Mars is one of the Solar System's largest impact basins: Hellas, with a diameter of 2300 km and a depth of over 7 km.

Hellas is thought to have formed between 3.8 and 4.1 billion years ago, when a large asteroid hit the surface of Mars.

Since its formation, Hellas has been subject to modification by the action of wind, ice, water and volcanic activity.

Impact craters have also since pock-marked this vast basin floor, two of which are the focus of this image, taken by the High Resolution Stereo Camera (HiRise) on ESA's Mars Express on 17 December 2013. The ground resolution is about 15 metres per pixel.

These craters lie in the deepest, western portion of Hellas, and such a clear view is unusual because dust clouds typically obscure the basin floor. Indeed, this region seems to be covered by a thick blanket of dust.

The larger of the two craters is about 25 km across. A flow of material appears to have been transported from the top left of the scene and into the crater.

Zooming in to the smooth mound and the area immediately around it reveals interesting textures that likely resulted from this flow.

Flow features are also seen outside of the craters, and in particular, at the centre left of the image near the top of the frame.

Material also seems to have cascaded from the larger crater's rim and into a neighbouring smaller crater, at the far left of the image.

The morphology of many features in the Hellas Basin and its surroundings strongly suggests the presence of ice and glaciers.

For example, in the foreground and around the crater rim, polygons of patterned ground are visible which indicates the presence of water, this pattern occurs when fine grained and porous wet soil freezes.

Indeed, in the deepest parts of the basin, the atmospheric pressure is about 89% higher than at the surface, which may even offer conditions suitable for water.

Radar images from NASA's Mars Reconnaissance Orbiter suggest that some craters in Hellas might contain water-ice glaciers several hundred metres thick, buried under layers of dust.

ESA Mars Express HRSC Image: Hellespontus Montes topography image

Credit: ESA

This is a colour-coded topography map of a portion of the western rim of the Hellas basin.

The crater shown in the upper left is on the periphery of this larger impact basin.

The edge of the Hellas basin is traced by a string of rocky peaks known as the Hellespontus Montes, revealed as the red/white ridge in this topography map thanks to their height.

White and red show the highest terrains, while blue and purple show the deepest.

The image is based on a digital terrain model of the region, from which the topography of the landscape has been derived.

The image was created using data acquired with the High Resolution Stereo Camera on ESA’s Mars Express on 13 January 2014 during orbit 12 750. North is to the right, east is up.

ESA Mars Express MARSIS: Penetrating Radar views Mars Geology

A radar view of the southern highlands of Mars, captured by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on ESA’s Mars Express. 

The radar track covers 5580 km and features the Hellas Basin at the far right, and the south polar ice cap with its associated layered deposits just left of centre. 

The gap to the left of the south pole is an artificial effect due to a distortion in the measurements; it does not correspond to any geological feature. 

Credit: ESA/NASA/JPL/ASI/Univ. Rome

There is much more to Mars than meets the eye. By using the MARSIS radar instrument on Mars Express, we can see several kilometres below the surface to see what lies beneath.

The radar creates subsurface images of Mars by beaming low-frequency radio waves towards the planet, which are reflected from any surface they encounter.

While most are reflected by the planet's surface, some travel deeper and bounce off interfaces between layers of different material, such as between rock, water or ice.

The strength and timing of the radar echoes that arrive back at Mars Express are a gauge of the depths of different types of underground interfaces.

This radar image is a 5580 km-long slice through the southern highlands of Mars created shortly after the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument (MARSIS) became operational in 2005.

The right-hand side is dominated by the vast Hellas Basin. It plunges 7 km below the surface and is about 2300 km wide, making it one of the largest impact basins in the Solar System.

The bright peak just left of centre is the south polar region of Mars. This is where the radar comes into its own, for beneath the cap of frozen carbon dioxide and water ice it reveals multiple layers of ice and dust.

This map shows the thickness of the south polar layered deposits of Mars, an ice-rich geologic unit that was probed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS).

Known as the South Polar Layered Deposits, this feature extends nearly 4 km below the surface. 

The layers are thought to arise from variations in the deposition of ice and dust as Mars experienced cycles of climate change.

Thanks to the radar, scientists have estimated that the amount of water trapped in frozen layers in the south polar region is equivalent to a liquid layer about 11 m deep covering the planet.