Mars 'not dry, arid planet', evidence shows

Liquid water has been observed on the planet Mars, the US space agency NASA said on Monday.

"Mars is not the dry, arid planet we thought of in the past," Jim Green, NASA's planetary science director, told a news conference. "Under certain circumstances, liquid water has been found on Mars."

Scientists have found the first evidence that briny water may flow on the surface of Mars during the planet's summer months, a paper published on Monday shows.