NASA scientists are reporting definitive signs of liquid water on Mars' present-day surface.

"This, I think, gives a focus of where we should look more closely," said Alfred S. McEwen, professor of planetary geology at the University of Arizona and investigator of high-resolution images taken on NASA's Mars Reconnaissance Orbiter.

Mars is known to have had rivers, lakes, and perhaps an ocean a few billion years ago. Moisture on Mars' surface today, however, has been modest. Scientists have known for a long time that water still remains on Mars, but in frozen form. There have also been signs of liquid water, but nothing was proven until recently.

More From 99.9 The Point