Photos taken by ESA’s Mars Express space probe show the Colles Nili region on planet Mars. It’s very ancient geological feature that mark the boundaries between the northern lowlands and the southern highlands with the remains of ancient glaciers around them. They show signs of glaciations that occurred on Mars during the last few hundred million years.

That boundary line is one of the oldest geological features of Mars with peaks and slopes that have a height difference of several kilometers between an area and the other. The hills are distributed as in some formations existing on Earth known as inselberg or monadnock, which emerge in the midst of a plain. Those might be hills that survived erosion and probably that’s also the case with the ones in Colles Nili.

According to one of hypotheses concerning the origin of the dichotomy, which is the topographic division between the the lowlands and the highlands, the northern hemisphere of Mars may have been hit by a large asteroid over four billion years ago. It may have “shaved off” several kilometers of young rock from the planetary crust.

In that area mounds of rocks were identified that are surrounded by layered deposits along the hill sides. Ridges and troughs are present in the bottom of the channels that surround those mounds and in some of the impact craters that formed in the course of time.

Mounds and ridges are associated with buried ice that was covered by dust and various debris carried in the course of time from the lowlands in the process of erosion. Similar features may bear the marks of a number of ice ages that occurred during several hundreds of millions of years and might exist in several boundary regions of Mars.

Subsequently, volcanic dust arrived from other areas created the streaks of darker material visible in various spots. They’re particularly visible on the right side of the image. Inside the main crater these materials accumulated to form some dunes.

This kind of geological feature shows once again the presence of water, which today is frozen, on Mars. These glaciers were hidden and a mapping work of territory conducted with a space probe and subsequent image analysis were needed to discover their signs. Colles Nili is another piece in the puzzle of the red planet’s history.