Roughly three billion years ago, the northern third of Mars was covered by a massive ocean, according to global databases of apparent river valley networks on the planet, including ancient deltas. "Our findings lend credence to the existing theories regarding extent and formation time of an ancient ocean on Mars," says University of Colorado-Boulder researcher Gaetano Di Achille (via Fox News). "Moreover, our test suggests that early Mars could have likely had a global water cycle similar to the present hydrological configuration of our planet." Another researcher calls the finding the "strongest evidence for an ocean on Mars presented to date," notes the Colorado Daily, though many questions remain, such as how long the ocean lasted and where the water went. Even more paramount: Was there ever life on Mars? NASA's next mission to Mars, one led by CU and launching in 2013, could help answer such inquiries.