The largest natural satellite (moon) in the solar system is:

Ganymede, a moon of Jupiter, is the largest moon in the solar system. With a diameter of about 5,268 km, it is even larger than the planet Mercury, although it has only about half of Mercury's mass.

Key facts about Ganymede:

• It was discovered by Galileo Galilei in 1610, along with three other large moons of Jupiter.
• It is named after a Trojan prince in Greek mythology who became cupbearer to the gods.
• It orbits Jupiter at a distance of about 1.07 million km and takes about 7 days to complete one orbit.
• It is tidally locked, so it always shows the same side to Jupiter.

Structure:

• Ganymede is made of roughly equal amounts of rock and water ice.
• It has an iron-rich core, a rocky mantle and an icy outer shell.
• Scientists believe it has a huge underground ocean of salty water beneath its icy crust, which may contain more water than all the Earth's oceans.

Magnetic field:

• Ganymede is the only moon in the solar system known to have its own magnetic field, produced in its liquid iron core.
• This creates a small magnetosphere inside Jupiter's much larger one, and causes faint auroras.

Surface:

It has two main types of terrain: dark, older, heavily cratered regions and lighter, younger regions with grooves and ridges.

Exploration:

NASA's Galileo spacecraft studied Ganymede in the 1990s.

The European Space Agency's JUICE (Jupiter Icy Moons Explorer), launched in April 2023, is expected to go into orbit around Ganymede in the 2030s. It will be the first spacecraft to orbit a moon other than the Earth's Moon.

Largest moons of the solar system (by diameter):

Ganymede (Jupiter), Titan (Saturn), Callisto (Jupiter), Io (Jupiter), the Earth's Moon, Europa (Jupiter) and Triton (Neptune).

Why not the other options?

• ✗Titan, Saturn's largest moon, is the second largest moon in the solar system.
• ✗Callisto, another moon of Jupiter, is the third largest.
• ✗The Earth's Moon is the fifth largest.