(Sen) - The European Space Agency's Mars Express orbiter has captured images of a deep channel carved into the Martian landscape which is believed to have been created by a river in the distant past.

Named Reull Vallis, the river-like channel stretches 1,500 kilometres and is almost 7 kilometres wide in places, and 300 metres deep. The valley is flanked by many tributaries, one of which can be seen on the main image. The orbiter's High Resolution Stereo Camera (HRSC) was used to take the pictures.

Along the floor of the valley are grooves that run parallel to its sides, and scientists believe these were scratched into the floor by the movement of debris and ice long after running water had carved out the valley. The scars are therefore evidence of glacial movement along the valley.

A computer generated perspective image of Reull Vallis created from data captured by the Mars Express orbiter. Credit: ESA/DLR/FU Berlin (G. Neukum)

To the side of the river channel is the Promethei Terra Highlands which rises to about 2,500 metres. The region shows similar characterists to regions on Earth affected by glaciation.

The images captured by Mars Express add to the growing body of evidence of how water once flowed on Mars. NASA's rover Curiosity, which is about to drill rock for the first time, found itself driving through an ancient river bed in Gale Crater. A recent report on the findings of NASA's Mars Reconnaissance Orbiter examined signs that a lake may once have existed in a Martian crater, fed from underground water.

The Mars Express orbiter was launched in June 2003 and arrived at Mars in December 2003. The spacecraft also carried the Beagle 2 lander which failed to return any data after landing.

The European Space Agency is responsible for the Mars Express mission.