liquid water has been observed on the planet Mars, the US space agency NASA said today. “Mars is not the dry, arid planet we thought of in the past,” Jim Green, NASA’s planetary science director, told a press conference. “Under certain circumstances, liquid water has been found on Mars.” Scientists have long believed that water once flowed freely across the red planet and was responsible for forming its valleys and canyons. Major climate change about three billion years ago is believed to have changed all that, Green said.