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Like Io, Europa orbits close to Jupiter and has sizable moons orbiting beyond it. The resulting gravitational effects also melt Europa\u2019s subsurface layer, but because this moon is composed mostly of water ice, its melted layer is a huge ocean of liquid water.<\/p>\n
Data collected by NASA\u2019s Voyager and Galileo missions suggest that under about 30 kilometers (19 miles) of ice, Europa may be holding an ocean 70-100 kilometers (43-62 miles) deep. Even though Europa is smaller than Earth\u2019s moon, its oceans are thought to contain twice as much liquid water as all of Earth\u2019s oceans and lakes combined.<\/p>\n
This could make Europa an especially promising place to look for life, because liquid water is crucial for life as we know it. Europa\u2019s subsurface oceans may have other life-friendly qualities as well, including protection from radiation. Europa\u2019s oceans also appear to be salty, which might mean that they could be in direct contact with a rocky seafloor below. Earth\u2019s oceans get most of their salt from hydrothermal vents in the seafloor, and these vents are among the most likely places where life first emerged on Earth. The basic ingredients for making life seem to be water, organic compounds, and an energy source, and the heat coming out of hydrothermal vents could have provided the energy needed to turn non-living ingredients into life.<\/p>\n
For all these reasons, Europa is an important target in the search for life beyond Earth. To better understand this world and its possible habitability, two missions are going to study Europa in the coming years: the European Space Agency\u2019s Jupiter Icy Moons Explorer (Juice), which launched in April 2023, and NASA\u2019s Europa Clipper, which is set to launch in 2024.<\/p>\n
Continuing our trajectory out from Jupiter, the next Galilean moon we come to is Ganymede. It is the largest moon in the Solar System, even bigger than the planet Mercury. It\u2019s also the only moon in the Solar System that has its own magnetic field.<\/p>\n<\/div>\n