Jupiter has 79 moons, 53 named and 26 unnamed, still waiting for their official name. Among them is a moon named Ganymede, is the largest satellite in our Solar System. It has it’s own magnetic field. It has a diameter of 5,268 km which is larger than Mercury and Pluto, and slightly smaller than Mars. It would be easily classified as a planet if it were orbiting around the sun rather than jupiter.  It is the ninth-largest object in the Solar System. It orbits around the Jupiter at a distance of 1070400 km.

Ganymede was discovered by Galileo Galilei on January 7, 1610. The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. Galileo called this moon Jupiter III. Its name was abandoned in mid-1800s and a new name was given as suggested by astronomer Simon Marius, after the mythological Ganymede, a Trojan prince desired by Zeus (the Greek counterpart of Jupiter), who carried him off to be the cupbearer of the gods.

Several spacecraft have flown by Jupiter and its moons. The first spacecraft explored Ganymede was Pioneer 10 in 1973 followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images and discovered Ganymede’s underground ocean and magnetic field.

The next planned mission to the Jovian system is the European Space Agency’s Jupiter Icy Moon Explorer (JUICE), due to launch in 2022 for arrival at Jupiter in 2030. While the mission will look at Ganymede, Callisto and Europa. Ganymede will be the focus and scientists will try to figure out more about its ocean and icy crust, map its surface in detail, learn about the interior, probe the atmosphere and study the magnetic field.

In February 2014, NASA and the United States Geological Survey unveiled the first detailed map of Ganymede in images and a video animation created using observations from NASA’s Voyager 1 and Voyager 2 spacecraft, as well as the dedicated Jupiter-orbiting Galileo spacecraft.

Ganymede has three main layers. A sphere of metallic iron at the center (the core, which generates a magnetic field) above which is a spherical shell of rock (mantle) and then the spherical shell of mostly ice surrounding the rock shell and the core. According to scientists the ice shell on the outside is very thick, maybe 800 km (497 miles) thick. The surface is the very top of the ice shell. Though it is mostly ice, the ice shell might contain some rock mixed in. Scientists believe there must be a fair amount of rock in the ice near the surface. Ganymede’s magnetic field is embedded inside Jupiter’s massive magnetosphere.


40 percent of the surface of Ganymede is covered by highly dark cratered dark regions and the remaining 60 percent is covered by a light grooved terrain, which forms intricate patterns across Ganymede. The grooved terrain is probably formed by tensional faulting or the release of water from beneath the surface. Groove ridges as high as 700m and runs for thousands of kilometres across Ganymede’s surface. The grooves have relatively few craters and probably developed at the expense of the darker crust. The dark regions on Ganymede are old and rough and the dark cratered terrain is believed to be the original crust of the satellite. Lighter regions are young and smooth.The largest area on Ganymede is called Galileo Region.

Scientists believe that Ganymede has a saltwater ocean below its surface. In 2015, a study by the Hubble Space Telescope looked at Ganymede’s auroras and how they change between Ganymede’s and Jupiter’s magnetic fields. The “rocking” seen by the auroras gives evidence that the probable ocean underneath is salty, more salty than oceans of Earth, scientists said at the time.

Some scientists believe that life may start in Ganymede. However there is so high pressure at the base of the ocean that any water down there would turn to ice. This would make it difficult for any hot-water vents to bring nutrients into the ocean. Because of which scientists believe extraterrestrial life would occur. This would be so fascinating to know about extraterrestrial life if it would exist in our own Solar System.