A long time ago, Mars was a world flowing with rivers and streams. We know this thanks to decades of work by robotic explorers and their teams on Earth.

What we don't know: did life ever thrive on Mars?

Now, the @NASAPersevere mission will take an even closer look. 1/4 The rover will set out on expedition across Jezero Crater, where a river once ran into a lake similar in some ways to lakes on Earth: go.nasa.gov/3s59WcX. There's even a river delta that looks remarkably like the one at the mouth of the Mississippi. 2/4