The 8 planets in the solar system have a total of 181 moons at the time of this writing. Although new moons are being discovered all the time, there are many interesting things to learn about the existing solar system moons. Of the 181 moons currently known about, in this article, we will be looking at the 10 largest moons.

Ganymede

Discovered January 1610 by Galileo Galilei, Ganymede is the largest moon of Jupiter and the 9th largest object in the solar system, which includes the sun. Ganymede is 3,275 miles in size and is the largest object without a substantial atmosphere. Its size means that it is 26 percent larger than the planet Mercury by volume, although it is only 45 percent as massive. It is the only moon in the solar system to have magnetic field and orbits Jupiter roughly once every 7 days. The moon is composed of equal amounts of silicate rock and water, and has a fully differentiated body with an iron-rich, liquid core. There is an internal ocean that may contain more water than all of Earth’s oceans combined. Beginning with Pioneer 10, several spacecraft have explored Ganymede, which the Voyager probes, Voyager 1 and Voyager 2, refining measurements of the size, while Galileo discovered its underground ocean and magnetic field.

Titan

Discovered in 1655 b Christiaan Huygens, Titan is the largest moon of Saturn being 3,200 miles in size and is the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and is the only known object in space other than Earth on which clear evidence of stable bodies of surface liquid has been found. Titan is 1 of 7 gravitationally rounded moons in orbit around Saturn, and the 2nd most distant from Saturn of those 7 that are gravitationally rounded. Titan is often called a planet like moon because Titan is 50% larger in diameter than the Moon of the Earth and is 80% more massive. Titan was the first known moon of Saturn, and the sixth known planetary satellite. Titan orbits Saturn once every 15 days and 22 hours and its rotational period is identical to the orbital period. Moreover, Titan is tidally locked in synchronous rotation with Saturn, which means that one side is shown to the planet permanently.

Callisto

Discovered in 1610 by Galileo Galilei, Callisto has a diameter of 2,995 miles. This makes Callisto about 99% the diameter of the planet Mercury, but only about a third of its mass. Tidally locked around Jupiter, Callisto is composed of approximately equal amounts of rock and ices. It has the lowest density and surface gravity of Jupiter’s major moons. The surface of Callisto is the oldest and most heavily cratered in the Solar System, with its surface being completely covered with impact craters. Callisto lacks signs or signatures of subsurface processes such as plate tectonics or volcanism. It is possible that Callisto harbors life and the moon does have a thin atmosphere.

Io

With an area of 2,264 miles, Io is the innermost and third-largest of the four Galilean moons of the planet Jupiter. Slightly larger than Earth’s moon, Io has the highest density of any moon, the strongest surface gravity of any moon, and the lowest amount of water of any known astronomical object in the Solar System. It was discovered in 1610 by Galileo Galilei and was named after the mythological character Io, a priestess of Hera who became one of Zeus’s lovers. There are more than 400 active volcanoes on Io, which makes it most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io’s interior as it is pulled between Jupiter and the other Galilean moons. The volcanism has been important in shaping the surface of the moons surface and as a result, the unique features.

Moon

With a size of 2,159 miles, the Moon is Earth’s only natural satellite. Of all the moons in the solar system, the Moon is most massive relative to its parent planet, with a diameter about 1/4th that of Earth. This makes the moons size comparable to the width of Australia. It lacks any significant atmosphere, hydrosphere, or magnetic field, but has a surface gravity roughly 1/6th of Earth’s. The only other moon in the solar system known to have a higher surface gravity and density than the moon is Jupiters Moon Io. It is thought that the moon formed as a result of a debris from a giant impact between Earth and another planet 4.51 billion years ago.

Because the moon is prevalent in the nights sky with a roughly 28 day regular cycle, numerous cultures have been influenced and reference the moon in their calendars, art, myths, and languages. In 1959, the USSRs Luna 2 spacecraft became the first artificial object to reach the moon, and in 1966, Luna 9 made the first successful soft landing on the surface. The only human lunar missions to date have been those of the US Apollo program, which landed a total of men on the surface from 1969 to 1972.

Europa

The smallest of the four Galilean moons orbiting Jupiter, Europa has an area of 1,940 miles. This makes it the sixth-closest to the planet of all the 80 known moons of Jupiter, Europa is a Galilean moon because it was discovered in 1610 by Galileo Galilei. The name Europa comes from the Phoenician who was the mother of King Minos of Crete and lover of Zeus. Although it is the smallest Galilean moon, Europa is just smaller than Earth’s Moon. Europa has the smoothest surface of any solid object in the Solar System. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath the surface, which could conceivably harbor extraterrestrial life

Triton

Triton is the largest natural satellite of the planet Neptune 13 moons, and was the first Neptunian moon to be discovered, on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet’s rotation. Triton is one of the few moons in the Solar System known to be geologically active. Triton has a surface area of 1682 miles, which is composed of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. During its 1989 flyby of Triton, Voyager 2  found surface temperatures of 38 K and also discovered active geysers erupting sublimated nitrogen gas.

Titania

With a size of 980 miles, Titania is the largest moon of Uranus. It was discovered by William Herschel in 1787, and named after the queen of the fairies in Shakespeare’s A Midsummer Night’s Dream. Its orbit lies inside Uranus’s magnetosphere. Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. It is possible that a layer of liquid water is present at the boundary of the core and mantle. Titania is covered with numerous impact craters reaching up to 203 miles in diameter, but is less heavily cratered than Oberon. Uranus and its moons has been studied up close only once, by the spacecraft Voyager 2 in January 1986. When Voyager 2 passed by Uranus and its moons, the spacecraft took several images of Titania, which turned out to be about 40% of its surface.

Rhea

Discovered in 1672 Giovanni Domenico Cassini, Rhea is the smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium. It has an area of 950 miles and is Saturn’s 2nd largest moon. Although discovered in 1672, Rhea was not named until 1847, when John Herschel that the names of the Titans, sisters and brothers of Kronos be used. Rhea is an icy body with a low density, which indicates that it is made of ~25% rock and ~75% water ice. This makes Rhea the 10th most massive moon.

Oberon

With an area of 946 miles, Oberon is the second-largest and second most massive of the Uranian moons. It was discovered by William Herschel in 1787 and is named after the mythical king of the fairies who appears as a character in Shakespeare’s A Midsummer Night’s Dream. The orbit lies partially outside Uranus’s magnetosphere. The moon consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the boundary between the mantle and the core. When Voyager 2 passed by Uranus and its moons, the spacecraft took several images of Oberon, which turned out to be about 40% of its surface.

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