More than 60 moons orbit Jupiter. One of these moons is Europa. It is especially intriguing to scientists. Miles below its cracked icy surface lies a deep saltwater ocean. Future missions to Europa will investigate these oceans for signs of life. If life exists, what kinds of organisms could survive in such a cold, dark place? To answer this question, scientists look to some of the most extreme environments on Earth.

Description: one of Jupiter's largest moons; entirely covered by a thick icy ocean
Discovered By: Galileo Galilei in 1610
Size: 1,940 miles (3,122 km) in diameter
Average Distance from the Sun:
778,340,821 kilometers (483,638,564 miles)
Average Surface Temperature: -162°C (-260°F )
Cool Fact: One day, a robot may study Europa's oceans. Today, these robots are being tested under the ice of Antarctica.

Image credits: main image, NASA.