Moons

Moons also known as natural satellites are astronomical bodies that orbit planets and asteroids. There are more than 200 moons in our Solar System. The inner planets of the Solar System have fewer moons as compared to the gas giants which have numerous moons.

Moons In Our Solar System

Interesting Moons Facts

  • Moon is an object that revolves around the planets and not directly around the sun.
  • They are called natural satellites of the respective planets.
  • The solar system is known to have more than 180 moons.
  • The number of moons ranges from none to more than a hundred moons for a single planet.
  • The inner planets of the solar system that is the first four planets have moons that are less in number as compared to the gas giants which have numerous moons.
  • Mercury does not have any moons.
  • Venus does not have any moons.
  • The earth has only one natural satellite that is called the moon.
  • Mars is known to have two moons called Phobos and Deimos.
  • Jupiter is known to have 79 moons by now. Out of the 79 moons of the planet, only 53 have been officially named.
  • Saturn has more than a hundred moons. However, only about 82 of these have been confirmed.
  • Uranus is known to have 27 moons.
  • Neptune is known to have 14 moons all of which are named after characters from Greek mythology.
  • The five moons of Pluto are named as Charon, Nix, Hydra, Kerberos and Styx.
  • Haumea is known to have two natural satellites which are named as Hiʻiaka and Namaka.
  • Makemake is known to have one moon which is currently referred to as S/2015 or MK 2.
  • Eris is known to have one natural satellite which is called as Dysnomia.

What are Moons?

Moons also called natural satellites are celestial objects that orbit planets and asteroids rather than the Sun. There are several variations in the composition and the number of moons that the planets of the Solar System have.

Number of moons ranges from none to more than a hundred moons for a single planet. The solar system is known to have more than 200 moons. The orbital periods of the moons can vary greatly depending on the size and the distance from their respective planets.

In general, the inner planets of the solar system that is the first four planets have moons that are less in number as compared to the gas giants which have numerous moons.

For example, the planets of Mercury and Venus have no moons at all while Jupiter has 79 moons and Saturn probably has more than 150 moons. Most of the dwarf planets also have moons.

Major Moons of the Solar System
Major Moons of the Solar System. Pic: https://upload.wikimedia.org/wikipedia/commons/4/4f/Moons_of_solar_system_v7.jpg

Mercury

Mercury does not have any moons.

Venus

Venus does not have any moons.

Earth

The Earth has only one natural satellite that is called the Moon. It has been named so because most people in ancient times did not have the knowledge about the fact that other planets have moons as well.

It was formed nearly 4.5 billion years ago. The Moon is by far the brightest object in the night sky. As it is very close to the earth it has been known to humans since ancient times and is visible to the naked eye very easily. It is the fifth-largest natural satellite in the entire solar system.

Distance, Size and Rotation

The moon is 384,400 km away from the earth and has a radius of roughly 1400 km. It takes about 29 days to complete one orbit around the earth. Because of it synchronized rotation only one side of the moon is visible to us from the Earth. The moon does not have light of its own and reflects back the light coming from the Sun.

Composition

The moon is mainly made up of silica, aluminum, and lime. It has a crust, a core, and a mantle. The core of the moon is rich in iron content and has a radius of nearly 240 km. A partially molten layer exists around the core which extends up to 500 km.

The mantle of the moon is made up of magnesium, silicon, iron, oxygen, etc. The crust of the moon is about 50 km thick. It is made up of elements like oxygen, magnesium, calcium, silicon, etc.

Phases of Moon

The moon is known to have many phases. The main phases of the moon include New Moon, crescent moon, gibbous moon, and full moon. Luna 2 by the Soviet Union was the first manmade object ever to reach the moon.

The moon is the only other astronomical object besides the Earth on which humans have set foot. As of now, 12 human beings have visited the moon. No evidence of life has been found on the moon.

Mars

Mars is known to have two moons called Phobos and Deimos. They have been named after the twin sons of Ares, the Greek God of war who was known as Mars to the Romans as their god of war.

The moons of Mars are irregularly shaped and are much smaller than the Earth’s moon. They are not visible to the naked eye from the Earth. However, they may be seen with the help of a telescope.

Phobos has around 22 km diameter while Deimos is smaller in size and is around 12 km in diameter. Phobos is around 9,400 km away from Mars. Deimos is farther away i.e. approximately 24,500 km away. Both of these moons were discovered by Asaph Hall in 1877.

It is not known how these moons originated. However, it is widely believed that these are asteroids captured from the asteroid belt. The orbits of both the moons are nearly circular.

Phobos rises in the west and sets in the east. It moves quickly. On the other hand, Deimos rises in the East and sets in the West. However, it is very slow. Jonathan Swift wrote about the two moons of Mars in his book ‘Gulliver’s Travels’ about 150 years before they were discovered.

Jupiter

Jupiter is known to have 79 moons by now. Out of the 79 moons of the planet, only 53 have been officially named. The four largest and most important moons of Jupiter are Io, Europa, Ganymede, and Callisto. These four moons are also collectively called Galilean satellites as they were discovered by Galileo Galilei.

The moon Io has the most active volcano in the entire solar system. The surface of Io is covered in sulphur. The orbit of Io is almost elliptical in nature.

Ganymede is the largest of all moons in the solar system. It is even larger than Mercury, which is a planet. It is also only slightly smaller than the planet Mars. In fact, it is the ninth-largest celestial body in the solar system. It is also the only moon in the solar system that has its own internal magnetic field.

It is believed that Europa might have liquid water on its surface. However, only ice caps have been found on it. Scientists believe that the total water on the surface of Europa could be twice as much as that on the surface of the Earth. It is also believed that Europa could sustain life.

All four Galilean moons are more than 3100 km in diameter. All the other moons are less than 250 km in diameter, most of them being irregular in shape. All the moons have different directions of spinning and different orbital periods ranging from 7 hours to 3 Earth years.

Saturn

Saturn has more than a hundred moons. However, only about 82 of these have been confirmed. Out of these 82, only 53 have been officially named. The moons of this planet vary greatly in size and shape. Only about 13 of the moons of the planet have a diameter of more than 50 km. Some moons also have their own rings.

Titan

The largest moon of Saturn is called Titan. It is also the second-largest moon in the solar system after Ganymede which is a moon of Jupiter. Titan has an atmosphere similar to that of the Earth it is rich in nitrogen.

It also has a landscape of dry river networks. It is unusual as such a system is not found anywhere else in the solar system. It is the only celestial body known, besides the Earth, to have liquid collect on its surface. It is believed that Titan has an ocean and several enormous lakes on its surface.

Titan was the first of Saturn’s moons to be discovered. It was discovered by Christiaan Huygens in 1655.

Some more Moons

Another important moon of Saturn is Enceladus. It has features similar to comets. It may also have liquid water on its poles and an ocean below its surface. Saturn has only 24 regular satellites. All the seven main satellites of Saturn are regular.

The planet also has 38 irregular satellites. Four more moons of Saturn were discovered between 1671 and 1684 by Giovanni Domenico Cassini. These moons were Tethys, Dione, Rhea and Lapetus.

In 1789, William Herschel discovered two more moons which were named as Mimas and Enceladus. In 1848, W.C. Bond, G.P. Bond and William Lassell collectively discovered Hyperion. In the 1970’s and 1980’s, NASA’s Voyager and Pioneer flew by Saturn and its moons.

However, detailed observations of the moons of the planet were provided by NASA’s Cassini. Cassini also discovered many moons that were previously not known.

Uranus

Uranus is known to have 27 moons. All of the planet’s moons are named after characters from plays written by William Shakespeare and Alexander Pope, unlike other planets whose moons are mostly named after Roman or Greek gods or mythological characters.

The moons of Uranus are divided into three groups. The first group consists of thirteen inner moons. The second group consists of the five major moons. The third group consists of nine irregular moons.

Titania is Uranus’ largest moon. It was one of the first two moons of the planet to be discovered, along with Oberon. The two moons were discovered by William Herschel in 1787. Titania is the eighth largest of the moons in the solar system. It is nearly 1580 km in diameter.

The next two moons which were discovered were Arial and Umbriel. They were discovered by William Lassell in 1851. Miranda, the last of the five major moons was discovered by Gerard Kuiper in 1948. Miranda is also the smallest of the five major moons. The last moon of the planet to be discovered yet is Margaret. It was discovered in 2003.

The inner moons of Uranus are composed of half rock and half water ice. Not much is known about the composition of the outer moons of the planet. They are believed to be asteroids that have been captured.

Neptune

Neptune is known to have 14 moons all of which are named after characters from Greek mythology. The largest moon of the planet is Triton which was discovered by William Lasswell in 1846, only a few days after the planet itself was discovered.

Triton consists of most of the mass of what is called the Neptunian Moon system. The second moon, Nereid was discovered almost a hundred years after the discovery of the first moon. The third of Neptune’s moons to be discovered was Larissa. It was discovered in 1981.

In 1989, NASA’s Voyager 2 discovered 5 more moons, namely, Naiad, Thalassa, Despina, Galatea and Proteus. In 2001, 5 more moons were discovered. These were named as Halimede, Sao, Psamathe, Laomedeia and Neso. By then totally 13 moons were discovered.

In 2002 another moon was sighted but was soon lost. So, it may have been a centaur or a comet. However, the size, dimensions and motion of the moon relative to the planet confirmed that it was a satellite, bringing the total to 14 moons.

This moon was called Neptune XIV. Neptune XIV has not yet been officially confirmed. Neso is the outermost moon of the planet. The distance between Neptune and Neso is the largest between any planet and its moon in the entire solar system.

The moons of Neptune are divided into two groups which are regular and irregular. All the 7 inner moons are regular moons. All the other moons, including Triton, fall into the second group. Proteus is the largest of the inner moon and the second largest of all the other moons of Neptune. 

Dwarf Planets

Most of the five dwarf planets of the solar system are known to have moons. The dwarf planet Ceres which is an asteroid does not have any moons.

Pluto

The five moons of Pluto are named Charon, Nix, Hydra, Kerberos, and Styx. The biggest moon of Pluto is Charon. Charon is roughly half the size of Pluto. It takes around six Earth days for Charon to revolve around the dwarf planet. Charon and Pluto together are sometimes called a double planet system. They are also the biggest planet-moon system in the entire solar system.

Nix and Hydra are small moons that were found using the Hubble Space Telescope in 2005. Kerberos is a very small moon. It is located between Nix and Hydra. It was discovered in 2011.

The latest moon of Pluto to be discovered so far is Styx. It was discovered in 2012. All of the moons of Pluto are named after mythological figures related to the underworld.

Haumea

Haumea is known to have two natural satellites which are named as Hiʻiaka and Namaka. Hi’iaka has a diameter of 310 km and orbits around Haumea every 49 days. Namaka has roughly 1/10 the mass of Hi’iaka. It orbits around Haumea every 18 days.

Makemake

Makemake is known to have one moon which is currently referred to as S/2015 or MK 2. The estimated diameter of the moon is 175 km. It has an orbital period of a little more than 12 days on earth.

Eris

Eris is known to have one natural satellite. It is called Dysnomia. It has been named after the Greek goddess of lawlessness. Eris and Dysnomia are the farthest known objects in the solar system as of today.

References

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