Scientists say they have found the most detailed evidence yet of long-flowing, ancient rivers on Mars. The discovery supports existing evidence that Mars, which today is dry and cold, was once a water-rich planet. The researchers say their findings suggest rivers may have flowed on the surface of Mars for hundreds of thousands of years. The evidence came from new satellite pictures of the Martian surface. These images were captured by a camera on NASA’s Mars Reconnaissance Orbiter. The camera is able to take detailed pictures of the surface while orbiting the planet from about 400 kilometers away.