(Sen) - Rocks that were evicted from the Martian ground during comet and asteroid impacts have revealed that water was a prominent underground feature for the first billion years in Mars’ history.

ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter have teamed up to study an area called Tyrrhena Terra in the southern highlands. The two spacecraft turned their instruments on a 1000 by 2000 kilometre region to study the chemistry of the rocks in the area and determine how water influenced the geology in ancient times.

The rocks in crater walls and rims were examined, along with surrounding liberated material, leading scientists to identify 175 sites that had minerals in them that can only be formed in the presence of water. The craters that were studied ranged from 1 to 84 kilometres across, and also had a range of depths. Deeper impact craters allow a more detailed look Mars’s history as they probe further beneath the surface.

“The composition of the rocks is such that underground water must have been present here for a long period of time in order to have altered their chemistry,” said Damien Loizeau, lead author of the study.

The rocks that were examined by the spacecraft were carved from depths of up to tens of kilometres and were formed before the craters were blasted into existence. The water thus flowed several kilometres beneath the surface 3.7 billion years ago. The water caused changes in the rocks depending on the temperature; low temperatures existed near the surface, where as high temperatures were incurred at greater depths. These temperatures were independent of surface conditions at the time.

Surface rocks in the region do not contain the same types of minerals that were caused by close contact with water.

“The role of liquid water on Mars is of great importance for its habitability and this study using Mars Express describes a very large zone where groundwater was present for a long time,” said ESA’s Mars Express project scientist Olivier Witasse.