A NASA probe will hurtle past Saturn's moon Enceladus on Wednesday, coming to within just 30 miles of the surface.
In the process, it will sample mist from a liquid ocean beneath the frozen surface. Doing so may provide clues about whether the ocean can support life.
At just 314 miles across, researchers originally expected Enceladus to be a tiny ball of solid ice. But thanks to NASA's Cassini probe, they now know it's somewhere really special.