Was young Mars warm and wet or cold and frozen?

3 Billion years is a long time. What if the red planet was blue?

via SyFy

In this new work, they looked at the valley networks, systems of interconnected tributaries that have been carved into the surface of Mars, mostly in the southern hemisphere and equatorial regions. On first glance, they look very much like river valleys on Earth, carved by flowing water that’s fed by either rain or a process called groundwater sapping, erosion from water that originally bubbles up from underground like in a spring or seeps out of rocks and sediment.

Read more.