In its latest postcard from Mars, the European Space Agency’s Mars Express returns to Acheron Fossae: a dramatic network of chasms carved into the surface of the Red Planet.
We live in an age of exoplanet discovery, and have discovered several thousand planets orbiting distant stars. These discoveries hold important lessons about planetary formation and solar system architecture. But we're also discovering a growing number of rogue planets, also called free-floating planets. These planets aren't gravitationally bound to any star. What can they teach us?

