London: Now cold and dry Red Planet had a warm and wet climate about four billion years ago, said researchers after analysing fossilised riverbeds discovered on an ancient region of the Martian surface. The team from the University College London identified over 17,000 km of former river channels on a northern plain called Arabia Terra, providing further evidence of water once flowing on Mars. "We've now found evidence of extensive river systems in the area which supports the idea that Mars was warm and wet, providing a more favourable environment for life than a cold, dry planet," explained led author Joel Davis. Since the 1970s, scientists have identified valleys and channels on Mars which they think were carved out and eroded by rain and surface runoff, just like on the Earth. Similar structures had not been seen on Arabia Terra until the team analysed high resolution imagery from NASA's Mars Reconnaissance Orbiter (MRO) spacecraft. The new study examined images covering an area roughly the size of Brazil at a much higher resolution. The team revealed the existence of many systems of fossilised riverbeds which are visible as inverted channels spread across the Arabia Terra plain. The inverted channels are similar to those found elsewhere on Mars and the Earth. "Arabia Terra was essentially one massive flood plain bordering the highlands and lowlands of Mars. We think the rivers were active 3.9-3.7 billion years ago, but gradually dried up before being rapidly buried and protected for billions of years, potentially preserving any ancient biological material that might have been present," added Davis. "These ancient Martian flood plains would be great places to explore to search for evidence of past life," noted Matthew Balme, senior lecturer at The Open University and co-author of the study published in the journal Geology. The European Space Agency's ExoMars Rover mission is set for launch in 2020.