Other than for a few days around the new Moon, our Moon is always visible from Earth. Using binoculars or a telescope, we can see moons orbiting Jupiter. These moons all orbit a planet. It may make you wonder about how many moons does the Sun has.
To answer this question best, we must understand what defines a planet and a moon. Before getting into too much depth, we will however answer the question directly.
The Sun has no moons. All of the moons in the solar system orbit planets. This is because of the definition of what a moon is.
In this article, we will first define what a planet is and then what a moon is. After that, we will detail the moons that we know of in the solar system.
What is a Planet?
A general definition of a planet is any large body that revolves around the sun in the solar system (Merriam-Webster). This is a little vague as it doesn’t describe how large is large enough. Astronomers use more specific criteria for what a planet is.
The International Astronomical Union is the organization that determines the scientific definition of a planet. At their general meeting in 2006, they redefined the definition. Unfortunately, Pluto was relegated to a dwarf planet because of this redefinition.
At the current time, these are the criteria that a body must satisfy to be called a planet in our solar system:
it must the Sun,
has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
has “cleared the neighborhood” around its orbit.
Basically, a planet must orbit the Sun, have enough mass for gravity to pull it into a sphere, and not have other similar-sized bodies orbiting at a similar distance from the Sun.
Unfortunately for poor Pluto, it failed the last criteria. Pluto is the largest trans-Neptunian object.
What is a Moon?
We need to be careful here. There is a difference between the Moon and other moons. The Moon is the Earth’s moon. If we are talking about moons that means moons other than our own.
A moon is a natural body that orbits another body in the solar system. To answer our question, this is of utmost importance.
If you have been reading carefully, you may already recognize the answer to the question about the number of the Sun’s moons.
How Many Moons Does the Sun Have?
Given the definition of a moon above, the Sun has no moons. All bodies that orbit the Sun are defined as another type of celestial body. These include planets, dwarf and minor planets, asteroids and comets.
All moons orbit other bodies in the solar system and not the Sun.
Which Planets Have Moons?
Other than Mercury and Venus, all the planets in the solar system have moons. Earth has one moon, while Mars has two. The gaseous outer planets have dozens of planets.
Earth
The most familiar moon to us is the Moon. It has fascinated humanity for millennia. The Moon has been both romanticized and studied for a long time. It may have had an essential influence on how life on Earth has developed.
Due to the force of gravity, the Moon causes tides in our oceans. The Sun also has an effect but not as greatly due to its distance.
The interaction of the Earth’s and Moon’s gravity results in the Moon being tidally locked to Earth. The result of this is that one side of the Moon faces us all the time. However, this does not mean that it doesn’t rotate. In fact, it rotates once each time it orbits the Earth.
While one side of the Moon always faces us, we can see 59% of the Moon’s surface from Earth. This is because the Moon wobbles on its axis a little. We call this lunar libration.
Mars
Mars has two irregularly shaped moons. Phobos and Deimos are the names of these moons. It is believed that they are captured asteroids.
Phobos orbits closer to the planet and makes a complete orbit in just 7.66 hours. Deimos orbits farther out and takes 30.35 hours to complete an orbit. (Wikipedia)
Phobos is the largest of the two moons. Unfortunately, it is not in a stable orbit. It is believed that the moon will collide with Mars in about 50 million years, unless it breaks up into a ring structure first.
Jupiter
While Jupiter is the King of planets in regard to mass, it does not have the most moons. However, it does have 95 moons. This is less than Saturn has.
While it doesn’t have the most moons, it does have the easiest moons to observe from Earth (other than the Moon of course). The four largest planets can be observed with binoculars or a small telescope. These planets are called the Galilean moons as they were studied in depth by Galileo Galilei.
The four largest moons of Jupiter are very interesting. Io is a world shaped by constant volcanic activity driven by tidal forces exerted on it by Jupiter. Europa has a skin of dynamic ice. Beneath the ice is believed to be water which may harbor life in some form. Ganymede is the largest moon in the solar system.
Saturn
Saturn has the highest number of moons in our solar system. To date, we have discovered 146 moons around Saturn.
Titan is the largest moon of Saturn. It is larger than any of the dwarf planets in the solar system (this includes Pluto). The moon is intriguing to scientists as it has a thick atmosphere. It has clouds, rain and running liquid on its surface. However, instead of water, it is methane. A mission is planned to survey the moon using a drone to fly between sites (Dragonfly).
Enceladus is the sixth-largest moon of Saturn. The Cassini mission discovered that this moon ejects icy particles from cracks in its ice. This is an indication that there is a liquid ocean beneath the ice.
The Moons of Jupiter are divided into three populations based on their orbit. There is an inner group and an outer group. The outer group orbit at a different angle to the inner group. The outer group is divided into two groups. One group orbits in the normal direction (prograde), while the second group orbits in the opposite direction (prograde). This indicates that the moons were captured in a variety of ways.
Uranus
Uranus has 27 known moons. The largest of these are Miranda, Ariel, Umbriel, Titania, and Oberon. They are named after Shakespearean characters.
Uranus rotates peculiarly. It seems to lay on its side. Interestingly the orbits of its moons are inclined in the same fashion. This clearly indicates that the planet had gained its moon after its axis was tilted. The planet’s tilt is likely the result of a collision with a large body.
Neptune
Neptune has 14 known moons (BBC). The largest of these is Triton. Surprisingly Triton was discovered just 17 days after Neptune was discovered. It took another 100 years before a second Neptune moon was discovered.
Triton orbits retrogradely (meaning it orbits in the opposite direction of the planet’s rotation). Due to this fact, it is believed that the moon was captured from a belt of small icy bodies found outside Neptune’s orbit (Kuiper belt).
Which Non-Planet Bodies Have Moons?
Pluto
As stated earlier, Pluto is a dwarf planet. Even so, Pluto has five moons. The largest moon Charon was discovered in 1978 nearly 50 years after Pluto was discovered. The moon is about one-eight the mass of Pluto.
Other dwarf and minor planets also have moons.
Asteroids
Asteroids are objects too small to be classified as dwarf or minor planets. At present, we believe that more than 150 asteroids in our solar system have moons (NASA). The first such moon found was orbiting around asteroid Ida. This moon was named Dactyl and is 1 mile (1.6 km) wide. Ida is 19 miles (30.5 km) wide.
The smallest asteroid found to have a moon is just 2460 feet (750 m) wide. Its moon is 558 feet (170 m). The asteroid is called Didymos, and the moon is Dimorphos.
Do Exomoons Exist?
As we have seen, our solar system has many moons. This leads to the question of whether planets outside the solar system (exoplanets) also have moons. Such moons are called exomoons.
To date, we have not found any exomoons. This is a result of how difficult it is to detect such bodies. There are studies underway to find them. A number of candidates have been identified.
It will not surprise anyone once we start detecting them.
How Many Moons are in Our Solar System?
At the current time, there are 285 known moons around planets. There are a further 467 moons orbiting asteroids, dwarf and minor planets. That’s a total of 752 moons in our solar system.
Final Thoughts
There you have it: the Sun has no moons.
However, nearly all the planets have moons. Moons are also found orbiting dwarf and minor planets, as well as even smaller objects.
If you watch the video below, remember that it is a little outdated with the number of moons that some planets have.
I found astronomy while working in dark rural locations. Initially, I explored the night sky and learnt the constellations before purchasing a pair of binoculars to further my knowledge of the sky.
My first telescope was a 200 mm Newtonian reflector on an equatorial mount. I found that this telescope had a steep learning curve but was a rewarding experience.
As time progressed, I became interested in astrophotography. This resulted in purchasing a 110 mm refracting telescope and a dedicated monochrome-cooled astronomical camera. This resulted in another very rewarding steep learning curve that far surpassed the experience with my first telescope.
I have joined Telescope Guru to share my knowledge of telescopes and astronomy.
