NATURAL SATELLITES: CHARACTERISTICS, FORMATION, FUNCTION, EXAMPLES - ARTE - 2024

Natural satellites are rocky bodies linked to planets by the force of gravity. Usually they are smaller than the planet they orbit. Natural satellites are also called "moons" because the Moon is the natural satellite of the Earth. The presence of these stars is quite common, because except for Mercury, Venus and Ceres, the other planets of the Solar System have moons orbiting around them.

The total number of moons in the Solar System is unknown, as it is believed that there are still many more to discover. Until now, the existence of 181 has been documented, of which the planet Saturn has the largest number: 82.

Some of the natural satellites of the solar system. Ganymede, followed by Titan, Callisto, Io, and the Moon are the largest. Venus has 0 moons Neptune has 14. User: primefac

Natural satellites do not have moons, however, there are asteroids that do, for example (243) Ida is an asteroid with a natural satellite: Dactyl.

The only natural satellite visible to the naked eye is our own Moon. To see the satellites of Jupiter you need a telescope. Galileo Galilei was the first to discover the four largest in 1610 and baptize them with mythological names: Io, Callisto, Europa, and Ganymede.

Since then, each new discovered satellite has been assigned a mythological name, with the exception of those of Uranus, which are named after characters from William Shakespeare.

This animation shows a natural satellite orbiting the parent planet. Source: Wikimedia Commons. Wiki-MG **** @@@ - fr Accueil fr: Accueil

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The origin of natural satellites dates back to the very formation of the solar system. The currently most widely accepted hypothesis is the nebular hypothesis: from the remains of a supernova, a nebula of cosmic gas and dust was formed, which thanks to the force of gravity agglomerated enough matter to create the Sun in the first place.

Once the Sun was created, a rotating disk of gas and dust remained around it, as has been observed in young stars, in which these disks are frequent.

The matter in the disk that surrounds the star is condensing as it cools and the particles that compose it collide. Over time, planetesimals were formed, the embryos of future planets, and in the same way satellites could form.

In this way cosmologists believe that all the bodies that the solar system contains were formed, including the Sun itself, planets, satellites, asteroids and comets. The process of agglomeration and compaction of matter is called accretion.

Now the question remains as to how each planet acquired its own natural satellites. In our solar system, the rocky planets or inner planets have few satellites. Mercury and Venus do not. The Earth has only one, which is the Moon, while Mars has two: Phobos and Deimos.

But the gaseous outer planets count their moons by the tens. So there are several theories that try to explain this:

-The satellites detached from the planet and remained in its orbit

-The planet captured the satellite

-Both the planet and the satellite formed a system from the beginning.

Movements of natural satellites

Size comparison between the Earth and the Moon. Apollo 17 Picture of the Whole Earth: NASATelescopic Image of the Full Moon: Gregory H. Revera

Gravitational interactions between bodies in the solar system lead to complex scenarios for the movement of satellites. These interactions modify the orbits and to the known movements of translation and rotation, others are added, such as librations.

The librations or hesitations of the Moon are oscillatory movements of the satellite that are observed from the Earth. Thanks to the librations, although the Moon always shows the same face to the Earth, a small additional percentage of the non-visible side can be seen.

The interactions also modify the appearance of the satellites and these in turn those of the planet around which they orbit. A little more will be said about this later.

Types of natural satellites

As for the types, the natural satellites can be, for example:

Regular satellites

Regular satellites rotate in the same direction as their parent planet around the Sun, so most likely they originated at the same time or are the result of some catastrophic event suffered by the planet in remote times.

Irregular satellites

They almost always rotate in the opposite direction to that of the mother planet (they are retrograde), and their orbit tends to have a greater eccentricity and they are more distant, for which they fall into the category of probable captured satellites.

Temporary satellites

They are usually small asteroids captured by the planet for a time, which then continue to penetrate into space. The small 2006 RH120, about 3 meters long, is believed to reach Earth orbit every 20 years and is captured there, although it may not be Earth's only temporary satellite.

There are also other names for natural satellites according to the effects they have on the planet or according to the configuration of its orbit.

Function

The natural satellites of the planets were not created to have any specific function, unlike artificial satellites. They exist due to multiple gravitational-type interactions and other physical processes that are still partly unknown.

Orbit

However, satellites have remarkable effects on the planets around which they orbit. It is enough to think about the effect of the tides to understand the enormous influence that the Moon has on the Earth.

And not only that, the Moon also contributes to shaping the Earth's orbit, so that if it were missing, the climate and living conditions here would be significantly affected.

Similarly, the moons of the other planets help to establish the orbits of their parent planets and to configure their characteristics.

Ring configuration

It is worth mentioning the case of the shepherd satellites on the outer planets, so called because with their gravity they help to maintain the configuration of the rings on planets like Saturn, the planet with the most notable rings.

Around Saturn there is a thin disk of material composed of very fine particles. The orbit of some of its moons, like Mimas, passes through the disk, separating it into rings. It is then said that the satellites gravitationally "graze" these rings, keeping the area that surrounds their orbit free.

Tidal forces

Tidal forces are present between a planet and its satellites, for example between the Earth and the Moon. They are due to the fact that both are extended bodies, that is, with measurable size.

So, the gravitational interaction between the two is not completely homogeneous, because there are points closer to each other, where the magnitude of the force of gravity is greater.

Remember that the gravitational attraction depends on the distance between the objects. If we want to calculate their value between the Earth and the Moon with Newton's equation, we usually do it by substituting their respective masses and the distance between their centers.

By doing it this way, we are assuming that the masses of both are concentrated right in the center.

But things change if you take into account a point on Earth located at a certain distance from the center. For example in the following figure, the gravitational pull of the moon (on the left) is slightly different at points A, B, C and D. At least we expect it to be stronger at point A, which is closer, and smaller at point B, which is farther away.

Figure 3. The tidal forces exerted mainly by the Moon, cause the oceans to rise towards it during high tides. Source: Wikimedia Commons. Eman.

Actually the difference is not too great, but it is enough to cause the terrestrial tides, since the oceanic masses, being fluid, are more easily deformable by the slight gravitational pull exerted by the Moon.

A similar interaction occurs between the Earth and the Sun, despite the fact that the Sun is much further away, but it must be taken into account that it is more massive.

High and low tides

Periodically the effects of the Moon and the Sun add up and then the tides are higher. This happens on a new moon or full moon, when the three stars are aligned. On the other hand, when they are at right angles the tidal effects counteract each other.

Tidal forces are not unique to the Earth - Moon system, but are also present throughout the solar system

Earth's natural satellites

View of the Moon, the only natural satellite of the Earth. Source: Max Pixels.

The only natural satellite of the Earth is our Moon. It is the largest satellite compared to the parent planet.

Although its surface is inhospitable, its influence is extraordinary for life on Earth: the force of its gravity altered the Earth's orbit, lengthening the period of light to allow time for plants to carry out photosynthesis.

On the Moon there is no breathable atmosphere, it lacks liquid water and has sudden changes in temperature. But thanks to it the seasons and tides occur, and it also transformed the Earth's atmosphere to make it breathable.

As if that were not enough, it serves as a guide for agriculture and is an eternal source of inspiration for scientists, philosophers, poets and lovers.

Natural satellites of Mars

Figure 5. Phobos and Deimos. Source: Wikimedia Commons. No machine-readable author provided. RHorning assumed (based on copyright claims)..

They are two small (about 10 km in maximum diameter) and irregular satellites discovered at the end of the 19th century by the North American astronomer Asaph Hall: Phobos and Deimos.

They probably came from the asteroid belt that separates the inner and outer planets and were pulled by Martian gravity.

They orbit very close to the red planet, with Phobos being the closest, in an orbit of 3000 km or less. Astronomers believe it will eventually crash onto the Martian surface. As for Deimos, it may possibly escape the gravity of Mars to become an independent asteroid.

Jupiter's natural satellites

Comparison of sizes between the Galilean satellites, the Earth and the Moon. Source: Wikimedia Commons. Hydra92.

The 4 largest satellites of Jupiter were discovered thanks to Galileo's newly released telescope, which is why they are called Galilean satellites. But the gas giant has no less than 79 moons so far, although the Galilean moons are the largest, comparable in size to the planet Mercury.

One of them, Io, has an atmosphere, makes a complete revolution around Jupiter in just under 2 days and has an average density similar to that of the Moon.

For its part, Europe is rocky and has a thin atmosphere. It takes less than 4 days to go around the planet and scientists believe that it has tectonic activity, just like Earth.

Ganymede and Callisto are the largest moons, taking a week to orbit. Ganymede, the largest of the moons in the entire solar system, has its own magnetic field, a thin atmosphere with oxygen, and may contain liquid water, as does Callisto.

Likewise, Jupiter has a large number of other moons, both regular and irregular, some possibly formed by a part of the same nebula that originated Jupiter by accretion. Others, especially the irregular ones, were surely captured by Jovian gravity when they happened to pass close enough to the planet.

Saturn's natural satellites

Mimas, satellite of Saturn in image taken from Cassini. Source: Wikimedia Commons.

Saturn is the planet with the most satellites, about 82 according to recent counts. They form a fairly complex system, in which the shepherd satellites, the Trojans, those that share orbits and a multitude of satellites stand out.

The most important, due to its size and because it has an atmosphere, is Titan. This moon is the second largest in the entire solar system, after Ganymede, and is visible from Earth with the help of the telescope.

By the mid-20th century Gerard Kuiper had already detected methane in Titan's atmosphere, but thanks to the Cassini-Huygens mission we now know that Titan is home to winds of up to 210 m / s.

For comparative purposes, Category 5 land hurricanes are the most intense and have winds with speeds of just over 70 m / s. Likewise, the rains on Titan are methane, so the outlook is unwelcoming.

Mimas is another interesting satellite of Saturn, although smaller than Titan. We mentioned him before as a ring shepherd. But what is striking about its icy surface is a massive impact crater named Herschel after its discoverer. In the center of the crater there is a mountain about 6000 meters high.

For his part, Iapetus is distinguished by having one side markedly darker than the other, although the reason is unknown. It also has its own gigantic impact crater 500 km in diameter, it is located at a great distance from Saturn, much farther than the other notable satellites, and the orbit is very inclined.

Natural satellites of Uranus

The Miranda satellite photographed from Voyager. NASA / JPL-Caltech

To date, 27 satellites of the planet Uranus have been counted, all devoid of atmosphere. Among them are shepherd satellites, just like on Saturn.

Two large groups of satellites are distinguished on Uranus: the interior and the exterior. The former are made from ice and rock, while the composition of the latter is still unknown.

Titania and Oberon are the largest satellites of Uranus, but the icy Miranda satellite, the smallest of the major satellites, is striking because of its chaotic surface, which appears to have suffered countless impacts, or perhaps an extremely violent one.

It is also possible that it has been greatly affected by the tidal forces caused by the parent planet Uranus and thus has that disturbingly cracked appearance.

Neptune's natural satellites

So far there are 15 satellites of Neptune and the most striking is also the largest: Triton. It is an icy world beyond imagination, because according to the data, the surface is at 37 K or -236.15 ºC.

At the poles, nitrogen and other frozen gases such as carbon monoxide and dioxide abound. Seen from space, Triton has a beautiful almost perfectly spherical shape, which sets it apart from the other, more irregular satellites of Neptune.

As for the other satellites of Neptune, these fall into the category of irregular satellites, so it is very likely that the planet has captured them at some point.

Pluto's natural satellites

Comparative size Earth-Moon and Pluto-Charon. Source: NASA via Wikimedia Commons.

The best known of Pluto's satellites is Charon, whose size is similar to that of the parent planet, which is why it is considered more of a binary system, rather than a planet and its satellite.

Charon was discovered in 1975, ruling out the possibility that Pluto had once been a satellite of Neptune. In addition to the Pluto-Charon binomial, there are four more smaller satellites, called: Nix, Hydra, Cerberus and Styx.

Pluto and Charon are in synchronous orbits, that is to say that the time they take to rotate around their axis is the same in which they travel the orbit.

References

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