Galilean moons

Jupiter’s four big­gest moons are very dif­fer­ent worlds

Sky at Night Magazine - - THE GUIDE -

Io

Di­am­e­ter 3,660km Mass 0.015 Earth masses Or­bital dis­tance 421,700km In brief Io, the clos­est moon to Jupiter, has over 400 vol­ca­noes across its sur­face. The gas gi­ant’s con­stant grav­i­ta­tional tug­ging keeps its in­te­rior molten.

Europa

Di­am­e­ter 3,122km Mass 0.008 Earth masses Or­bital dis­tance 670,900km In brief The small­est of the moons, Europa is cov­ered in a thick layer of ice. Be­neath this is a liq­uid wa­ter ocean that could be hos­pitable to life.

Ganymede

Di­am­e­ter 5,268km Mass 0.025 Earth masses Or­bital dis­tance 1,070,400km In brief The largest moon in the So­lar Sys­tem. It is thought to have a large rocky core cov­ered with lay­ers of ice and wa­ter which show signs of tec­tonic ac­tiv­ity.

Cal­listo

Di­am­e­ter 4,821km Mass 0.018 Earth masses Or­bital dis­tance 1,882,700km In brief The least ac­tive of the Galilean moons. Its an­cient sur­face is al­most com­pletely cov­ered in craters, so ev­ery new crater erases an older one.

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