Top sights to see on Ganymede

There is a huge contrast on the surface of Ganymede, as there are two distinctly different types of terrain. Covering 60 per cent of the Jovian moon is a relatively young, bright surface, covered by an array of ridges and grooves. Conversely, Ganymede also exhibits an old, dark, heavily cratered terrain. After investigating the density of the craters, scientists suggest that the oldest craters formed around 4 billion years ago.

Scientists believe that this contradicting terrain is a result of tectonic plate activity replenishing the surface, much like we see on Earth. In this case, it’s most likely that the newer surface originated from a subsurface ocean, which had been indirectly confirmed by the Hubble Space Telescope in 2015. It is this internal saline ocean that has led to the intriguing and fascinating surface, and also the moon’s magnetosphere. It is because of the plate tectonics that a lot of ancient craters have been lost below the surface.

The older regions, – also be referred to as Regiones – have the orignal craters from the intense bombardment in its early history. These are much darker regions, as they have more contaminated water ice from the interior, causing it to have a lower albedo - a measurement of reflectivity.

A peculiar aspect of the craters is the lack of a central depression. When a crater is mentioned, most people will automatically think of a ring in the ground with the surface declining as you reach the centre of it. However, this is not the case for Ganymede’s craters, they have almost no height and are flat. This is thought to be down to the slow adjustment to the icy surface, and this can also be referred to as a palimpsest.

Over time, the surface of Ganymede has been stretched and ripped apart. This could be due to plate tectonics or the release of internal water, creating a series of grooves and ridges, which can be cited as a sulcus. These sulci – named after their resemblance to our brain’s grooves – individually extend for thousands of kilometres all across the surface. Because of fresh water dispersing from the moon’s interior and immediately freezing because of the cold temperatures, this creates a newer, shinier surface.

It's because of these features astronomers are constructing JUICE (Jupiter Icy Moons Explorer), a spacecraft to examine Ganymede, Europa and Callisto, in an attempt to understand the oceans under their icy and cracked surfaces. This could potentially reveal a habitable environment, which would be ground-shattering news in the astronomical community.

“It is because of the plate tectonics that a lot of ancient craters have been lost below the surface”

Crater chain Across the surface are a series of crater chains, known as catenae. These lines of closely spaced craters may originate from comet or asteroid fragments.

Older, cratered terrain These heavily cratered regions tell us a lot about the moon’s ancient history, but they are often separated by planetary fractures, or sulci.

Young, groovy surface The lighter material on the surface of Ganymede is filled with a beautiful series of grooves and ridges, which appear to have replenished the moon’s surface.

Galileo Regio The largest area on Ganymede with a diameter of 3,200 kilometres (1,988 miles). The lighter material appears to enclose this timeworn, dark region.