Handout of the surface of the planet Mars
Handout of the surface of the planet MarsReuters

European Space Agency's Mars Express captured a striking picture of a huge river in the upper Reull Vallis region of Mars, revealed the agency.  The image captured by its high-resolution stereo camera last year shows a river-like structure that stretches 1,500 km across the surface of Mars.

Scientists believe that the river channel visible in the pictures was formed when a huge river ran through the Promethei Terra Highlands of the planet, before flowing to the floor of the vast Hellas basin at some point of time in Mars' history.

The 3-D images released by the agency also shows a large area of the Reull Vallis with one of the tributaries of the river cutting through the valley. In some images captured, the channel is seen as wide as seven kilometre with a depth of 300 metres.

Although the images show a single tributary, scientists say that the river is flanked with numerous tributaries throughout the stretch.

The Promethei Terra Highlands, a range of mountains with soft rounded tops, are visible on one side of the river.  These mountains are about 2,500 meters above the ground level and are surrounded by large impact craters.

According to the scientists, the river might have been formed by water in the Hesperian period between 3.5 billion and 1.8 billion years ago and has structures that are similar to those on Earth's surface.

"This region shows a striking resemblance to the morphology found in regions on Earth affected by glaciation. For example, we can see circular step-like structures on the inner walls of the sediment-filled crater in the foreground of the second perspective view. Planetary scientists think that these may represent former high water or glacial levels, before ice and water sublimated or evaporated away in stages at various times," the ESA said in its statement.

Click here for images.