The European Space Agency (ESA)’s Mars Express orbiter has captured this image of the Martian surface, showing the boundary between the planet’s north and south hemispheres. The two hemispheres are strikingly different. The northern hemisphere of Mars is generally smooth and flat, consisting of low plains with few impact craters. The southern hemisphere, however, is mountainous and covered in craters, with many areas of past volcanic activity.
To see the boundary between the two more clearly, the ESA also released this colored version of the image which represents elevation. The purple and blue areas are low, while the yellow and reds have higher altitudes. The bottom half of the image shows a high ridge, with a boundary beyond which lower plains lie.
The area which separates the two hemispheres is called a “dichotomy boundary.” In this area, there are broken sections of ground called “fretted terrain,” and in this particular image, the region of fretted terrain is called Nilosyrtis Mensae.
“Nilosyrtis Mensae has a labyrinthian appearance, with numerous channels and valleys carving through the terrain,” the ESA explained in a blog post. “Water, wind and ice have 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 area is of interest not only because it is a boundary region, but also because it may contain clues to the history of water on Mars. There are ridges and grooves on the surface in the area which seem to have been made by a flowing material such as ice. At a distant time in the planet’s history, ice glaciers may have flowed across the surface of the planet, leaving impressions in the rock which are still visible today.
