Knowra Galilean moons Galilean moons The four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto—first observed by Galileo Galilei in 1610. Their changing positions showed that celestial bodies could orbit a planet other than Earth.
Laplace resonance : A 1:2:4 orbital resonance linking Io, Europa, and Ganymede. Their repeated gravitational alignment helps sustain Io’s tidal heating and Europa’s internal ocean.
Galileo spacecraft : A NASA spacecraft that orbited Jupiter from 1995 to 2003 and studied the planet and its moons. Its measurements transformed knowledge of the moons, including evidence for Europa’s subsurface ocean.
Galileo Galilei : An Italian astronomer and physicist who used telescopes to make landmark observations of the heavens. He observed the moons in January 1610 and published the discovery in Sidereus Nuncius.
Io : Jupiter’s innermost Galilean moon, marked by intense volcanism and a largely sulfurous surface. Its eruptions reveal how strongly orbital tides can heat a moon’s interior.
Titan : Saturn’s largest moon, with a dense nitrogen atmosphere and lakes of liquid hydrocarbons. Unlike Jupiter’s four large moons, Titan has a substantial atmosphere and surface lakes.
Tidal heating : Internal heat generated as gravitational tides deform a body's interior. Jupiter’s changing pull powers Io’s volcanism and may keep Europa’s ocean liquid.
Europa Clipper : A NASA mission designed to investigate Europa’s ice shell, ocean, and potential habitability. It will make repeated flybys to assess whether Europa has environments suitable for life.
Sidereus Nuncius : Galileo’s 1610 pamphlet reporting telescopic observations of the Moon, stars, and Jupiter’s satellites. It announced the observations that established the moons as a new astronomical discovery.
Europa : Jupiter’s icy Galilean moon, whose fractured surface overlies a likely global ocean. It is the group’s clearest candidate for a potentially habitable subsurface environment.
Earth's Moon : Earth’s natural satellite and the fifth-largest moon in the Solar System. Its orbit around a planet offers a familiar contrast to the four moons orbiting Jupiter.
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