solar jup moon

The Gas Giant is home to 79 moons. However, scientists are particularly interested in those known as Galilean satellites.

Jupiter is more than just the king among the planets. It’s also the gas giant with the most moons. Researchers believe that Jupiter may have 79 moons. Only 53 moons have been identified, and others are still awaiting official designation.

While all of Jupiter’s moons are worth looking at, four of them stand out: The Galilean satellites. These are Jupiter’s largest moons. They include Io, Europa Ganymede, Ganymede, Callisto, and Ganymede. The satellites were first seen by Galileo Galilei, an astronomer, in 1610. But what is it that makes these four special moons?


Ganymede has the distinction of being the solar system’s biggest moon. It is also the only natural satellite that has its magnetic field. Ganymede, due to its magnetic field is able to produce its own north lights around the region near its north and southern poles.

Hubble, 1996. Hubble found evidence Ganymede has an oxygen atmosphere. Researchers think however that it’s too thin to support the existence of life as we know.

Ganymede’s surface consists of a predominately cold and crisscrossed collection o old and new (er) terrain. It is possible that the original crust of the satellite may still be present in the dark regions. The lighter areas are more youthful and smoother, which could be the result either of tensional faulting (or the release from water below Ganymede).


Callisto might not be the largest of the moons (its Jupiter is second and third largest), but it’s the most heavily-crater object in our solar system. This led scientists to consider Callisto an “ugly duckling” and they believe that Callisto is hiding a secret. Galileo data suggests a salty ocean may be below the surface.

Researchers estimate that the ocean could be as far as 155 miles (225 kilometers) below its icy crust. Callisto’s satellite’s interior may contain layers of ice that mix with rock and metal. This could mean that it might be supporting life.


Io (pronounced “EYE-oh”) is the world with the most active volcanoes in the solarsystem. It has hundreds of volcanic cones. From some of these, lava fountains rise up to dozens miles high. Io’s high activity is due to the combination of Jupiter, Europa, Ganymede and their gravitational tugging of war.

Io, Jupiter’s third-largest Moon, is a little larger than the Moon. It is tidally tied to Jupiter. This means that one side never faces the other planet while it orbits. The Moon is similarly tied to Earth. Io’s orbit revolves in an elliptical manner, and unlike the Moon’s circular orbit. This makes the moon subject to tremendous tidal forces. Io orbits around the Earth, so the gravitational effect on one side is greater than the other. This causes Io’s outer surface to bulge. Earth is experiencing the same effects due to the Moon. While the Moon affects Earth’s tides by bringing them to heights of around 60 feet (18 meters), Io’s surfaces fluctuate by as high as 330ft (100m).

Jupiter also has to contend with Io. Io crosses Jupiter’s Magnetic Field at 262,000 miles (422,000km) orbit, turning the moon in to a gigantic electric generator. Io creates lightening by cutting back to Jupiter from the current it generates.

Io is chaotic, and even though life can be found in most inhospitable areas on Earth (including the most remote ones), most scientists don’t believe Io will host any.


Voyager spacecrafts made contact with Europa in 1979. It was then that scientists began to suspect that the moon might contain an ocean of liquid. Every science fiction scenario has ever been imagined for alien life thriving in a Europan Ocean.

Scientists are not the only ones who are interested in life on this moon. Europa’s crust is about 10 to 15 mile (15 to 25km) thick. Under it lies an ocean 40 – 100 miles (60 – 150km) deep. Europa could hold twice as much water than all the oceans of Earth combined. This is a body that measures only one quarter of the planet’s width.

Hubble’s Space Telescope has also detected signs of water leaking into space. If this happens, it will be possible for a spacecraft that is orbiting Europa to take a sample from its ocean.

Europa seems to have the only problem of not having an energy source. This is one of the major requirements Astrobiologists believe are essential for life. Jupiter is approximately 5.2 Astrological Units from Earth. 1 AU represents the average distance between Earth and the Sun. Any sunlight reaching Europa is therefore 25 times fainter that at Earth. NASA’s Galileo spacecraft discovered signs of convection happening in Europa’s Ice Layer, even though sunlight isn’t a great energy source. Galileo explored Jupiter from 1995 to 2003. It discovered domes and pits on Europa’s surfaces during this time. Heating from below could have caused the cooler, dense ices to sink and the warmer, more liquid ices to rise.