Where a river once flowed on Mars 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.