10 largest satellites in the universe

Review of the best according to the editorial board. On the selection criteria. This material is subjective, does not constitute advertising and does not serve as a purchase guide. Before buying, you need to consult with a specialist.

The universe is an amazing and mysterious place. It works according to laws that we can only remotely imagine. Even the famous general theory of relativity, to the creation of which Albert Einstein had a hand in, describes the principle of the formation of celestial mechanics only in the most general terms.

But it is already possible to imagine how the stellar and planetary systems work. There is a heavy object, smaller objects rotate around it under the influence of gravity, and around them – even smaller ones. Actually, this is why all more or less large planets have satellites that move in an annular orbit.

But sometimes these satellites are much more impressive than the planets themselves. Liquid water found in objects around Saturn! At the same time, Saturn itself is a gas planet, which may not even have a surface in the usual sense of this term. Therefore, in some cases, the satellites are more interesting than the planets themselves.

And for those who want to be surprised by the peculiarities of celestial mechanics, we have collected the largest satellites in the universe. Unfortunately, at the moment, human technologies can hardly see even distant planets, so most of the satellites from the rating are in our home solar system.

An overview of the largest satellites in the universe

Nomination	a place	name	The size
Rating of the largest satellites in the universe	1	Titania, satellite of Uranus	1578 KM IN DIAMETER
	2	Triton, satellite of Neptune	2707 KM IN DIAMETER
	3	Europa, moon of Jupiter	3122 KM IN DIAMETER
	4	The Moon is the Earth's satellite	3475 KM IN DIAMETER
	5	Io, moon of Jupiter	3643 KM IN DIAMETER
	6	Callisto, moon of Jupiter	4821 KM IN DIAMETER
	7	Titan, moon of Saturn	5150 KM IN DIAMETER
	8	Ganymede, moon of Jupiter	5268 KM IN DIAMETER
	9	Kepler-1625b 1, satellite Kepler-1625b	49244 KM IN DIAMETER
	10	WASP-12b 1, satellite WASP-12b	81548 KM IN DIAMETER

10th place: Titania, satellite of Uranus (1578 km in diameter)

Rating: 4.1

On January 11, 1787, astronomer William Herschel observed Uranus and discovered that this planet has at least two huge moons. And the biggest of them is Titania. By the way, the name of this celestial body was given by the son of Herschel in honor of the fairy queen from the works of William Shakespeare.

For a long time, only Herschel had a sufficiently powerful telescope to observe this object. Now Titania can be seen through amateur models. However, a sufficiently accurate and detailed photograph of the surface of this object was obtained only in 1986, when the Voyager 2 research probe flew past the surface.

Due to its availability for observation, quite a lot is known about Titania. Even maps of its surface have been compiled, and the most significant relief elements bear their own names. By tradition, place names are invented by the names of heroes and the names of places from the works of Shakespeare. For example, the longest canyon on the surface (1492 km long) is called Messina, after the city of Messina, where the comedy Much Ado About Nothing takes place.

Infrared spectroscopy has confirmed that there is water ice on Titania's surface. In addition, frozen carbon dioxide was discovered at the poles of the satellite. And its origins are controversial. Typically carbon dioxide is a decomposition product of organic matter or carbonates.

The very surface of Titania is painted in a dark red color. There is no atmosphere, although some researchers believe that during warm seasons, carbon dioxide can melt, creating a small shell around the satellite.

9th place: Triton, satellite of Neptune (2707 km in diameter)

Rating: 4.2

Six of the eight planets in the solar system revolve counterclockwise around the central star (as viewed from the north pole of the Earth). Neptune's thirteen moons also revolve counterclockwise around the planet. And only Triton, the largest of the satellites, violates this principle. Its movement is retrograde, that is, clockwise when viewed from the north pole of Neptune.

There may be several reasons why this 2,707-kilometer-long object does not rotate like the other 13 of its companions. But researchers believe that Neptune, flying past the Kuiper belt, grabbed this moon with its gravitational field. Since then, Triton has been rotating in the opposite direction.

Triton is interesting not only for its retrograde motion, but also because it is one of the few geologically active satellites. Volcanoes periodically erupt on its surface, only they emit not the usual lava, but practically solid nitrogen. Also, this satellite is dotted with traces of tectonic activity and is distinguished by an intricate relief.

It is very cold on the surface of Triton. The average temperature is about -235 degrees Celsius. That is why nitrogen is not in a gaseous state, but in a snow-like state. The surface itself is covered with a thick layer of ice – only not water, but methane or nitrogen. That is why Triton reflects sunlight well – and as a result, it was discovered in 1846.

8th place: Europa, satellite of Jupiter (3122 km in diameter)

Rating: 4.3

One of the largest moons of Jupiter, Europa, got its name not from a part of the world, but in honor of a character in ancient Greek mythology. At the time when it was opened, the western half of Eurasia had not yet become a separate geographic region. Europe was discovered by the famous Italian astronomer and physicist Galileo Galilei, and the official date is January 8, 1610.

To locate Europa, Galileo used a homemade refractor telescope with a 20x magnification. That is, today this satellite can be seen in the ungazed sky using an amateur device, even of an initial class. And in 1610 it was the most important discovery.

Europe has a remarkably flat surface with high reflectivity and virtually no craters or faults. The satellite is covered with ice, and under its layer, as scientists assume, is a liquid ocean of water. Therefore, some researchers believe that it is on this satellite that the presence of extraterrestrial life can be checked.

Interestingly, Europa's surface is also covered in 'freckles'. According to astronomers, they were formed from a mixture of warm and cold ice. In places of 'freckles', heated material from the ocean floor rose to the surface, bringing with it dark mud.

7th place: Moon, satellite of the Earth (3475 km in diameter)

Rating: 4.4

The moon is the only natural satellite of the Earth and one of the largest satellites in the solar system. It is so huge that it affects the planet with its gravitational field. The ebb and flow of the sea occurs precisely due to the fact that the water is attracted by the Moon and moves after it.

The moon has been known to mankind since time immemorial. Still – it is visible on the horizon almost every night, and in some cases it can be seen during the day. Moreover, the Moon is currently the only extraterrestrial object in the Universe that has been visited by humans. For the first time people landed on it on July 20, 1969.

Despite the many scientific directions and studies of the Moon – whole areas of knowledge such as selenology have been allocated to this satellite – humanity still does not know exactly where it came from at all. According to one of the theories, it arose due to the fact that once upon a time magmatic masses separated from the Earth and ended up in space. According to the other, the Moon existed as a separate quasi-planet, and then was captured by the Earth's gravitational field. Another hypothesis is called the 'Giant Collision Theory'. She suggests that the celestial body Teia once crashed into the Earth, which separated a significant part of the substance from the planet. It, in turn, under the influence of gravitational forces took a spherical shape and turned into the Moon.

The Moon is currently being considered as a possible colony space. However, progress in this direction is proceeding extremely slowly for a number of reasons. The lunar colonies offer very little scientific interest and almost no economic interest.

6th place: Io, moon of Jupiter (3643 km in diameter)

Rating: 4.5

Io is another moon of Jupiter discovered by Galileo Galilei using a homemade refractor telescope with 20x magnification. In total, the scientist registered four satellites of the gas giant – and all of them are presented in our ranking. Like other moons of Jupiter, Io is named after a character in Greek mythology.

Io is known for its incredible geological activity. Now it houses over 400 active volcanoes! This makes Io the most geologically active object in the solar system.

The reason for this activity is gravitational influence. Io is constantly in the fields of gravity of three large space objects – Jupiter, Europa and Ganymede. Since there is no water on the surface of the satellite, 'ebbs' and 'ebbs' are observed under the crust – in liquid magma and a straightened core. So volcanoes on Io are due to the attraction of other space objects. And during eruptions, a mixture of sulfur and sulfur dioxide rises to a height of up to 500 kilometers!

In addition, Io's silicate surface undergoes constant compression. Because of this, mountains appear on it, and some of them are impressively huge. For example, the summit of South Boosavla is located at an elevation of 17 kilometers!

Io even has an atmosphere of its own, made up of gaseous sulfur and sulfur dioxide. And it is caused just by constant eruptions. In addition, streams of matter escaping from under Io's crust enter the plasma torus around Jupiter.

5th place: Callisto, moon of Jupiter (4821 km in diameter)

Rating: 4.6

In January 1610, Galileo Galilei, observing Jupiter through a telescope, discovered four satellites of this gas giant. Callisto is one of them. And it is farther from the planet than everyone else. Like other 'Galilean satellites', it is named after a character in ancient Greek mythology.

Callisto is one of the most promising satellites of Jupiter. If mankind ever wants to master this gas giant, or at least study it closer, the 'transshipment' station should be located on this satellite. More or less adequate climatic and geological conditions and an insignificant level of radiation make Callisto a comfortable place – of course, in comparison with other satellites of Jupiter.

At the end of the last century and the beginning of the current one, Callisto was studied by the spectroscopic method. It turned out that the surface of the satellite is covered with silicates and water ice, as well as carbon dioxide and some organic compounds. However, the large number of craters also suggests that Callisto does not have an atmosphere in the usual sense of this term (or it is significantly thinner). In addition, there are no traces of volcanic and geological activity on the satellite – as on the Moon, for example.

4th place: Titan, satellite of Saturn (5150 km in diameter)

Rating: 4.7

Titan is the largest moon of Saturn and the second largest in the solar system. And thanks to its structure, it looks like a full-fledged planet! So, on its surface there are lakes with liquid. True, this is not water, but a mixture of ethane and methane. Titan is also surrounded by a dense atmosphere.

Titan was first spotted in 1655. Due to the dense nitrogen atmosphere with clouds of methane, its surface remained indistinguishable for a long time. Only in 2004, when the Cassini-Huygens probe flew past the satellite, scientists were able to see dark lakes of liquid on yellowish silicate soil.

Many researchers compare conditions on Titan with those on Earth at the beginning of its development. And this is despite the fact that the temperature on the satellite's surface is far from the resort temperature, up to -180 degrees Celsius. But scientists still assume that the simplest forms of life can exist on the satellite – for example, in underground reservoirs.

In 2004, the Huygens probe landed on the surface of Titan and was able to transmit a photograph. Rounded stones are distinguishable on it. This suggests the existence of erosion in the form of both winds and precipitation. In addition, in 2006, Huygens transmitted several radio spectral images, thanks to which it was possible to find out that the satellite also has high mountain ranges and dry river beds. All this makes Titan even more similar to Earth, albeit in the early stages of its existence.

3rd place: Ganymede, moon of Jupiter (5268 km in diameter)

Rating: 4.8

Ganymede is the largest moon of Jupiter, and indeed in the solar system. It was discovered, as usual, by Galileo Galilei on January 8, 1610. Interestingly, Ganymede is a large, but not heavy satellite. With a diameter of 5268 km, it is only 2 times the mass of the Moon.

Much of Ganymede's surface is covered with silicate rocks and water ice. The latter is especially abundant at the poles. Some researchers believe there is an ocean of liquid water at a depth of 200 km. And the core of Ganymede is hot, liquid and rich in iron, like most objects of the planetary type with a hard crust.

Ganymede has its own magnetosphere (other satellites in the solar system cannot boast of this). It is believed to have originated from a metallic core made of molten iron. True, the magnetosphere of Ganymede is extremely small and is completely hidden by the magnetosphere of Jupiter, introducing only slight distortions into the latter.

Ganymede also has an atmosphere. For the most part, it consists of oxygen in its various allotropic modifications – from atomic to ozone. There is also an insignificant hydrogen content. Also, during the study of the satellite by the Galileo apparatus, it turned out that it contains carbon dioxide, sulfuric acid and some organic compounds.

Ganymede, like other large moons, casts a shadow over the planet. On April 21, 2014, she found herself right on Jupiter's Great Red Spot – and it looked like an eye.

2nd place: Kepler-1625b 1, satellite Kepler-1625b (49244 km in diameter)

Rating: 4.9

As mentioned earlier, due to the imperfection of optical technologies, we can not yet detect relatively small satellites in exoplanets (that is, planets outside the solar system). It remains to observe only a few of the largest, and one of them is the Kepler-1625b 1 object.

The Kepler-1625b 1 satellite orbits the planet of the same name in the constellation Cygnus, orbiting the yellow dwarf Kepler-1625. It was discovered by the transit method back in 2017, but scientists still argue about its existence. This object is really huge – its dimensions are similar to the dimensions of the planet Neptune in the solar system.

The planet Kepler-1625b itself is supposedly a gas giant like Jupiter. And it 'acquired' an exoloon millions of years ago during its initial formation. At this time, a cloud of rarefied heated matter revolved around the star, which, under the action of gravitational forces, began to 'stick together' into planetoid objects. One of them turned out to be larger and captured the other with its gravitational field.

Both objects of the Kepler-1625b system are located in the so-called 'habitat radius' – that is, they are located close enough to their sun-like star that, in theory, life could arise on them. However, the planet itself is a gas giant, and this already somewhat complicates the process of the formation of organisms.

1st place: WASP-12b 1, satellite WASP-12b (81,548 km in diameter)

Rating: 5.0

In 2012, astronomers at the Pulkovo Observatory observed the star system WASP-12 and discovered a rather unusual nature of its brightness. This made it possible to assume that there are not only exoplanets, but also an exmoon near one of them.

WASP-12b 1 is potentially not only the largest known satellite in the universe, but also the hottest. Due to its very close location to the local 'sun', the temperature on its surface is about 2.5 thousand degrees Celsius. The size was determined by the amplitude of the brightness – it is 6.4 times the diameter of the Earth, or about 81.5 thousand kilometers.

Scientists suggest that WASP-12b 1 is an exmoon in the process of its formation, and at some point it will simply collapse onto the surface of the star. The point is, she's too close. Therefore, it is unlikely to be able to exist in a stable form for at least several billion years.

Observations are further complicated by the fact that the star WASP-12 is very far away – at a distance of 870 light years. It is a sun-like yellow dwarf, which is similar to our star in both size and mass.

---

Attention! This rating is subjective and does not constitute an advertisement and does not serve as a purchase guide. Before buying, you need to consult with a specialist.