Europa

An ocean hidden under the ice

Europa is a smooth white ball covered in ice, with reddish cracks. Under the ice lies a giant ocean — with twice as much water as all of Earth's oceans! Scientists think there could be life in that dark ocean. The Europa Clipper spacecraft is on its way to find out.

Europa (radius 1,561 km) is Jupiter's fourth-largest moon, orbiting every 3.55 days. Its surface is an ice shell 15–25 km thick — the smoothest surface in the Solar System (no tall mountains or deep craters). Beneath it lies a salty ocean 60–150 km deep, kept liquid by tidal heating from Jupiter. The reddish lines (lineae) are cracks where water has risen up. Hubble has spotted plumes of water vapour. If the seafloor has hydrothermal vents, microbes could live there — which makes Europa one of the most promising places to search for life. NASA's Europa Clipper (launched 2024) arrives in 2030.

Fun facts

• Europa holds 2–3 times more water than all of Earth's oceans.
• Europa's ice is so smooth it's called 'the billiard ball of the Solar System'.
• On Europa a day equals a year: it spins once for every orbit around Jupiter.