Jupiter and Its Moons

Half of Ultimate Cycle Catcher's routes end at Jupiter, and three of them take place entirely in a Jupiter-centered view. The giant planet's moon system is a miniature solar system of its own, and it is the toughest part of the tour.

The giant at the centre

Jupiter is the largest planet by far, more than eleven times Earth's diameter and over 300 times its mass. It orbits the Sun at about 5.2 times Earth's distance, taking nearly twelve years per lap. A minimum-energy transfer from Earth would take around two and a half to three years, which is why real missions usually add gravity assists. Jupiter has no solid surface; what we see are bands of cloud in an atmosphere of mostly hydrogen and helium, including a storm larger than Earth that has lasted for centuries.

Jupiter also has an immensely powerful magnetic field that traps charged particles in intense radiation belts. Any crewed traffic among its moons would need careful shielding, especially close to the planet.

Io, the furnace

Io is the innermost of the four large moons, slightly bigger than our Moon, and it circles Jupiter in about 1.8 days. It is the most volcanically active body known in the solar system, with hundreds of volcanoes and lava lakes. The heat comes from tides: Io's orbit is kept slightly oval by its neighbours, so Jupiter's gravity squeezes and relaxes it on every lap. The Io Furnace route takes its name from this, and from the fact that Io is the fastest of the large moons you chase.

Europa, the ice world

Europa, a little smaller than our Moon, orbits in about 3.6 days. Its bright surface is a shell of water ice crossed by cracks and ridges, and strong evidence suggests a global ocean of salty liquid water beneath it, kept warm by tidal heating. That makes Europa one of the most interesting places to look for conditions suitable for life beyond Earth.

Ganymede, the largest moon

Ganymede is the biggest moon in the solar system, larger than the planet Mercury, and orbits Jupiter in about 7.2 days. It is the only moon known to generate its own magnetic field, and it too probably hides a deep ocean between layers of ice.

The 1:2:4 resonance

Io, Europa and Ganymede are locked together. For every single orbit Ganymede completes, Europa completes two and Io four. Because of this lock, the three never all line up on the same side of Jupiter, and their mutual tugs keep the orbits slightly oval, feeding the tidal heat in Io and Europa. In the game this pattern is modelled directly, which is why the Europa Ice Run has a repeating rhythm you can learn.

Callisto, the outer sentinel

Callisto is the outermost large moon, almost as big as Mercury, with an orbit of about 16.7 days. Its ancient surface is one of the most heavily cratered in the solar system. Callisto lies outside the most intense radiation belts, so it has often been suggested as a base for future human exploration of the Jupiter system. The Callisto Long Haul route captures the contrast between slow Callisto and fast Io: a cycler plunging between them changes speed dramatically.

Amalthea, the speedster

Amalthea is a small, reddish, potato-shaped moon about 170 kilometres long that orbits well inside Io's orbit, completing a lap in about 12 hours. Its closeness to the planet makes it the fastest target in the game, used for the SKIM and PERIJOVE legs. Perijove is the point in an orbit that comes closest to Jupiter.

Why a Jupiter-centered view

Inside the moon system, Jupiter's gravity overwhelms the Sun's, so describing motion relative to Jupiter is natural. The game switches to this frame when a route arrives at the giant planet, and the Grand Tour Finale ends with a run through all four large moons in it.

Useful numbers

• Orbital periods: Amalthea about 0.5 days, Io 1.8, Europa 3.6, Ganymede 7.2, Callisto 16.7.
• Jupiter's orbit around the Sun: about 11.9 years.
• Ganymede's diameter: about 5,270 km.

Back to the science overview, or play the Jupiter routes.