Nilosyrtis Mensae, Mars: Dramatically Different Regions of the Red Planet Come Together as One

Mars is very much a world of two halves – as highlighted by this new image from ESA’s Mars Express, which shows where the planet’s dramatically different hemispheres come together as one. This image comprises data gathered on September 29, 2019, during orbit 19908. The ground resolution is approximately 15 m/pixel and the images are centered at about 69°E/31°N. This image was created using data from the nadir and color channels of the High-Resolution Stereo Camera (HRSC). The nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface. North is to the right.

Mars is very much a world of two halves, as this new image from ESA’s Mars Express highlights, showing where these dramatically different regions come together as one.

The morphology and characteristics of the martian surface differ significantly depending on location. The northern hemisphere of Mars is flat, smooth and, in places, sits a few kilometers lower than the southern. The southern hemisphere, meanwhile, is heavily cratered, and peppered with pockets of past volcanic activity.

A transition zone known as ‘dichotomy boundary’ separates the northern lowlands and southern highlands. Large parts of this region are filled with something scientists call fretted terrain: blocky, broken-up, fragmented swathes of terrain where the rough, pockmarked martian south gives way to the smoother north.

This new image from the Mars Express High-Resolution Stereo Camera (HRSC) shows exactly that: a region of fretted terrain named Nilosyrtis Mensae.

Nilosyrtis Mensae has a labyrinthian appearance, with numerous channels and valleys carving through the terrain. Water, wind, and ice been strongly affecting this region, dissecting and eroding the terrain, along with changes in martian geology: valleys have formed over time and sliced across the region, and once-defined impact craters have slowly degraded, their walls and features gradually wearing away.

The large crater to the right of the frame is an example of this degradation: it has a smooth, rounded appearance, with gently sloping walls, softened edges, and a flat bottom that has been widened and filled by sedimentary material over time. This worn-away morphology reflects both the crater’s advanced age, and the levels of erosion it has undergone since it formed.

Such erosion processes also created rounded hills and isolated flat-topped hills, or ‘mesas,’ that are visible within the crater and across the region more widely. These stand apart from their surroundings as isolated features, and contribute to the blocky, fractured appearance of fretted terrain.

Scientists are interested in Nilosyrtis Mensae not only for its location in this intriguing transition zone between north and south, but also for the secrets it could hold about the history of water on Mars.

Observations of this region by missions such as Mars Express have revealed ridges, grooves and other surface textures indicative of flowing material – most likely ice.

The climate and atmosphere of ancient Mars allowed ice and snow to accumulate and move around across the planet’s surface.

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