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These images, recently acquired by DLR's High Resolution Stereo Camera (HRSC), show dune fields and several periglacial formations in the southern polar region of Mars. This is a factual description of the image content, but one might also see an angel and a large heart formed from the dark sands. It is just as if Earth’s neighbouring planet were getting ready for the holiday season.

HRSC has been mapping the Red Planet in unprecedented resolution, in three dimensions and in colour, since 2004 as part of ESA's Mars Express mission. HRSC was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and constructed in collaboration with partners in industry. HRSC is operated by the DLR Institute of Planetary Research. Mars Express provides new data on the geology, mineralogy and atmosphere of Mars, in order to gain insights into the climate history of Earth’s neighbouring planet and to clarify the role and location of water that is still present.

Summer at the south pole on Mars makes an angel and its heart visible

A 'seasonal angel' with a heart sends greetings from the Martian south pole. The dark angel and the heart, both consisting of volcanic sands, are located in the southern polar region of the planet, not far from the polar cap, at approximately 78 degrees south. Currently it is summer at this location. The permanent ice cap, consisting mostly of water ice and frozen carbon dioxide, now has a diameter of 400 kilometres and an average thickness of 1.5 kilometres. These are dimensions that are roughly comparable to the ice-covered island of Greenland on Earth. However, it is only this size in the southern summer. During the six-month winter, the south pole ice cap on Mars extends further, to almost 60 degrees south. Even in summer in the southern hemisphere of Mars, temperatures never rise above zero degrees Celsius. In winter, temperatures down to minus 133 degrees Celsius cause the carbon dioxide from the atmosphere to freeze and fall onto the ice cap as snow. This blanket of carbon dioxide ice is between one and two metres thick and sublimates again with the next spring, thus evaporating and re-exposing the landscape. Only on the permanent ice cap of the south pole does a thin layer remain. The atmosphere on Mars contains very little water vapour that can freeze to form ice. Water vapour forms only 0.02 percent of the planet's gas envelope, which consists mainly of carbon dioxide and nitrogen; on Earth, there is twenty times more water vapour in the atmosphere, averaging a concentration of 0.4 percent. Therefore, the angel and the heart are only visible in the southern summer; in winter they lie hidden under the layer of frozen carbon dioxide.

The angel's head – an impact crater

In the upper centre of the images, an impact crater approximately 15 kilometres across can be seen, in which dark sands form the 'angel's head’. With a little imagination, the almost one-thousand-metre-high crater rim can even be interpreted as a halo. In several places, the layered deposits of the polar cap, consisting of ice mixed with dust, are clearly visible on the upper slopes. Even in the oval depression that forms the 'angel's hand', the view of the layered polar deposits is unobstructed.

The southern part of the image (on the right in images 1,4 and 6 ) is also covered by stratified deposits. These consist of ice and dust as well, but they are much more finely layered, thinner and cover the south polar deposits. This type of deposit covers large parts of the high latitudes of Mars (approximately between 40 and 80 degrees north and south respectively), which is why it is referred to as a 'latitude-dependent mantle'. In many places, degradation phenomena due to erosion and sublimation of the ice in spring and summer are visible in the mantle, which has created several small geological windows in which the finer layer structure can also be seen on close inspection.

In the centre of the image, beneath the angel's outstretched wing, is a large, heart-shaped depression bounded by a scarp leading to another large dark dune field. The dark material, consisting of olivine and pyroxene minerals, may have come from deeper layers of deposited volcanic eruptive material or could have been blown into the depression. In the latter case, the edges of the terrain would have acted as windbreaks, causing the sands to slow down and be deposited there. This dark material is distributed globally on Mars and forms imposing dune fields in countless impact craters.

Dust devils 'vacuum' the surface

On the left side of the images, numerous dark, intersecting lines can be seen on a very flat and bright surface. These are dust devil tracks, meaning traces left by numerous aeolian forces, caused by atmospheric turbulence. They leave these dark tracks on their path by 'sucking up' the lighter surface dust.

All images in high resolution and more images acquired by the HRSC instrument can be found in the Mars Express image gallery on flickr.

• Image processing
  

  These images were acquired by the High Resolution Stereo Camera (HRSC) on 8 November 2020 during Mars Express orbit 21,305. The resolution is approximately 15 metres per pixel. The centre of the images is located at approximately 148 degrees east and 78 degrees south. The perpendicular colour view was generated using data acquired by the nadir channel, the field of view which is aligned perpendicular to the surface of Mars, and the colour channels of HRSC. The oblique perspective view was computed using a Digital Terrain Model (DTM) and data acquired by the nadir and colour channels of HRSC. The anaglyph, which provides a three dimensional view of the landscape when viewed using red-green or red-blue glasses, was derived from data acquired by the nadir channel and the stereo channels. The colour-coded topographic view is based on a Digital Terrain Model (DTM) of the region, from which the topography of the landscape can be derived. The reference body for the HRSC DTM is a Mars equipotential surface (Areoid).

  HRSC was developed and is operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The systematic processing of the camera data was performed at the DLR Institute of Planetary Research in Berlin-Adlershof. Personnel in the Department of Planetary Sciences and Remote Sensing at Freie Universität Berlin used these data to create the image products shown here.

• The HRSC experiment on Mars Express
  The High Resolution Stereo Camera (HRSC) was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in collaboration with partners in industry (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Ralf Jaumann, consists of 52 co-investigators from 34 institutions in 11 countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.