An orbiting Nasa satellite has spotted an ancient, dried-up river on Mars - with the sort of branching tributaries we see in rivers on Earth, reports Yahoo News.

Millions of years ago, liquid water carved the surface of Mars, Nasa scientists believe - and ancient rivers such as this one could offer clues to the planet's early climate.

The image was captured by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

Mike Mellon of the University of Colorado says, 'Early in Martian history, liquid water energetically carved the surface, forming channel systems that look remarkably similar to river valleys and drainage networks on Earth, Yahoo News reports.

'Exactly how these channels formed—by rainfall, snowmelt, or seepage from underground springs—is often debated.

'The answer has important ramifications about the early Martian climate. Clues about the source of the water may indicate the shape, layout, and scale of the various tributaries in a channel system.'

'Our image shows an example of just such a water-carved channel. The channel pattern, called "dendritic" because of its tree–like branching, begins at the top of the image and runs down over the rim of an ancient impact basin across the basin floor.'