At first glance, Europa — the Jovian moon widely believed by scientists to be a prime candidate for harboring extraterrestrial life — appears unremarkable. It is mostly off-white and covered in tiny cuts known as "lineae" that appear as scratches on the surface, giving Europa the look of a scuffed-up pool cue ball. Yet despite its waiting-room-ecru shade, Europa is so intrinsically interesting that NASA has fixated on the moon as an object of study — which is why the agency is planning for the upcoming Europa Clipper mission (scheduled for 2023), where they hope among other things to learn about the water that covers the celestial body.
Part of the moon's appeal is that many of its secrets are hidden below its icy crust. Because Europa is constantly stretched by tidal forces from the gravity of the largest planet in the solar system, its interior is believed to have liquid oceans, though it lies beneath at least 10 to 15 miles of surface ice, planetary scientists say.
