Image by NASA - Wikimedia Commons (CC BY-SA 3.0)
Size comparison of Ganymede, the Moon and Earth
In recent times, a number of my science posts have been about naturally occurring satellites, I’ve written about Titan, Enceladus Europaand a number of the other Galilean moons moons. It is quite fascinating that in most of this moons, water has been discovered to be present within its layers, with the exception of Titan, that possess methane and ethane on its surface. Studies suggest that sometime in the future, life will be discovered in one or more of these moons, and I am a firm believer of this hypothesis because water and heat are major ingredients in making life possible, and a number of these moons possess these resources already.
Today, I hope to discuss yet another Galilean moon known as Ganymede, which is the biggest moon in our Solar System, and the only satellite that has its own magnetic field. This moon’s magnetic field results in the creation of auroras around its south and north poles, auroras which as beautiful glowing ribbons of electrified gas. Known as the ninth largest object in our Solar System, Ganymede is bigger than Mercury and the dwarf planet Pluto, although it is slightly smaller than Mars, which is almost the same size as Earth, this tells you how large Ganymede is for a moon. No doubt, this moon is quite fascinating, it possesses a metallic core, and it the third moon that orbits Jupiter (Galilean moon). The Galilean moons are the first sets of solar bodies that were discovered to be orbiting another planet.
There are a couple of fascinating things about this moon, starting from its name, which got its roots from the cupbearer of the ancient Greek god - Zeus. Alongside the other three Galilean Moons, Ganymede was discovered in 1610 by Galileo Galilei. Being the first moon ever to discovered at the time, it helped early astronomers to understand how solar bodies orbits. Early astronomers believed that our Solar System revolves around the Earth, but the discovery of Ganymede helped correct that notion that planets orbits around the Sun.
This moon consists of 3 layers, the core of Ganymede, (which is where its magnetic field is generated) is spherical in nature and consists of a metallic iron at its centre, the core is engulfed by a spherical shell made up of rock, then there is another spherical shell that consists mainly of ice that surrounds both the core and rocky shell. Then there is the thick outer covering which is made of ice that is about 497 miles in thickness that holds all three layers together. The topmost layer of Ganymede is made of ice, it is believed to be made of a mixture of ice and rock, as scientists believe that it's possible to have a fair amount of rock as well as the dominant ice that makes up the surface of this moon.
As of now, the atmospheric condition of the moon cannot support life, 22 years ago, the Hubble Space Telescope discovered clues that Ganymede has a very thin oxygen in its atmosphere. With this, it is very unlikely that there is any living thing on this cold moon. This 4.5 billion-year-old satellite, that is almost the same age as its hot star - Jupiter. Orbiting Jupiter takes Ganymede about seven Earth days, Ganymede is a cold world, with day temperature at its surface ranging from 171 - 297oF, and night-time temperatures reaching -193oC. As mentioned earlier, Ganymede is the only moon that possesses its own magnetic field or magnetosphere, a magnetic field is customarily found in planets such as Jupiter, Earth or Mars. According to Space.com
A magnetosphere is a comet-shaped region in which charged particles are trapped or deflected.
There have been several spacecraft shuttles across Jupiter and the moons that orbit this Jovian planet. First, there was Pioneer 10 that arrived in 1973, one year after, Pioneer 11 visited. There were some flybys done by both Voyager 1 and 2, this mission reveals striking images of the world. Later, the Galileo spacecraft produced more detailed images, after descending as low as 261 km above the surface of the Galilean moons.
The European Space Agency is currently working on a mission to Jupiter, the JUICE mission is scheduled to leave the Earth’s atmosphere sometime in 2022, and is anticipated to arrive at Jupiter in 2030. As the full meaning of the mission which is JUpiter ICy moons Explorer, it suggests that the focus is to look at the Galilean moons of Jupiter except for Io. But the focus of the mission is going to Ganymede, reasons being that this icy world displays how it can evolve and sometime in the future, it can be habitable. This mission will help scientist understand more about Ganymede’s icy crust, subsurface ocean, and creating an accurate map of its surface. It will also help scientist figure out more about the Ganymede’s atmosphere, its interior as well as its magnetic field.
Scientist argues that Ganymede subsurface ocean is consist of salt water. A 2015 study by Hubble Space Telescope which entailed having a critical look at the auroras found on Ganymede, and the changes that occur between the magnetic fields of Jupiter and Ganymede. The back and forth movement the auroras are observed to make is an indicator that the ocean beneath this moon is probably salty, scientists at the time believe this ocean to be saltier than the oceans here on Earth are.
It is quite unlikely the Ganymede can support life, at least not in the foreseeable future, and this is due to the internal structure of the moon. Due to the high-pressure levels at the floors of the ocean, this will turn all the water available into ice, hence, making it hard for hot vents to introduce nutrients to this water body. This is one of the ways that researchers believe extraterrestrial life can be made possible.
References
NASA - Jupiter’s Moon - Ganymede
Space - Jupiter’s Largest Moon
Space - Facts about Jupiter's Largest Moon
