"The atmospheric pressure on Mars is very low compared to that on the Earth, which means that water boils at a much lower temperature than it does on Earth," co-author of the paper, Susan Conway, said. "On the Martian surface the pressure is five to 10 millibars meaning that liquid water boils no matter what the temperature is."

But, surely if the surface of Mars had boiling water etching out its plains, we would have seen it in more than just experimental conditions, right? That's where the most exciting part of the research comes in. It turns out, we've already seen it happen. We just didn't know what we were looking at.

Even before scientists confirmed the existence of flowing water on Mars, they'd long suspected it, particularly due to some images showing landscapes on the planet changing with the seasons. In these images, you can even observe the water as it (very, very slowly) flows from season to season, like in this gif showing Martian slopes transitioning from spring to summer.

The warmer it gets, the further the water flows, even though, technically, the summer temperatures should be too cold. This is because, instead of the water we're used to seeing in our own streams and rivers here on Earth, the water that flows on Mars is a salty-brine which lowers the freezing point of the water, kind of like antifreeze. Even that explanation, however, still leaves a major unanswered question — and one that, until now, scientists were pretty unsure about how to solve.