Scientists have known that water flowed on Mars at one point, but until now, what that flow looked like has remained educated speculation. Now a discovery changes that. Mars rover Curiosity has found gravel that was once part of an ancient stream. This image shows the Martian rock outcrop where that gravel is.
There's a few facts we already know. Scientists started taking a closer look, and from the size of the gravel, we know the speed of the water in the stream (about three feet per second) and its depth (between ankle- and hip-deep). The roundness of the stones in the gravel even indicate they traveled long-distance, from above the rim of the Gale Crater (the slope of the crater is Curiosity's destination). We can also tell it wasn't a rare event; the stream flowed for years.
The bits of gravel varied in size from grain of sand to full-on golf ball, according to a statement from NASA. That means it couldn't have just been blown over by wind. Water made it happen.
So now that it has this find under its belt, what else is Curiosity searching for? More evidence of life. From NASA's statement:
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.