SATURN: CHARACTERISTICS, COMPOSITION, ORBIT, STRUCTURE - ARTE - 2025

Saturn is the second largest planet in the solar system after Jupiter. Known for its ring system, it belongs to the planets called Jovians, which are located after the asteroid belt, which separates them from the rocky planets.

Known since ancient times, as it is one of the 5 planets visible to the naked eye and the furthest from them, Galileo was the first to observe it with a telescope in 1610. Although he noticed the deformation caused by the rings, the lack of resolution of the instrument did not allowed him to distinguish its shape.

The gaseous planet Saturn, compared to Earth, 95 times smaller. Source: Saturn image: NASA / JPL / Space Science Institute Earth image: NASA / Apollo 17 crew / Public domain.

It was years later, in 1659, that Christian Huygens aptly described the famous rings. A short time later, the Italian astronomer Giovanni Cassini realized that the rings had a division, which is now called the Cassini division.

Although astronomers of antiquity could not detail the ring system, the already magnificent view of the planet must have impressed them enough to give it names such as "Alap Sahmas" (star of the Sun) for the Chaldeans, "Phaenon" (bright as the Sun) for the Greeks or "Khima" (responsible for the universal flood) for the Hebrews.

The ancient Romans associated the planet with the Greek god Cronos, father of Zeus, whom they called Saturn. In honor of this deity, the festivals called Saturnalia were celebrated in December, which the ancient Christians later associated with Christmas.

Other ancient cultures such as the Hindus, Chinese and Mayans also have observations of the planet in their records. For the Mayans, the dates on which the conjunctions of Saturn, Jupiter and Mars occurred were festive.

General characteristics of Saturn

Saturn is not as big as Jupiter, it is only a third of its mass, while its radius is 16% smaller.

It is the least dense of the planets; at 687 kg / m ^{3 it} could float on water if there were an ocean big enough to contain it. It is composed mainly of hydrogen and helium, the lightest elements known, although it contains others in a much smaller proportion.

Saturn has its own magnetic field, less intense than Jupiter's, but much more than Earth's, with the magnetic axis parallel to the axis of rotation. That is why auroras are common in the form of concentric circles, right in each polar region. These are formed by the movement of electrically charged particles in the middle of the intense magnetic field of the planet.

Another distinctive feature of Saturn is the heat it spews out into space, radiating almost twice the energy it receives from the Sun. Saturn's interior is very hot and scientists believe it is due to the condensation of liquid hydrogen at high pressure..

The pressure inside Saturn is a million times greater than the Earth's atmospheric pressure. The liquid hydrogen droplets pick up speed as they travel towards the center of the planet, producing heat.

Liquid hydrogen behaves like a metal, and is not only responsible for the radiated heat, but for the dynamo effect that creates the magnetic field.

Saturn's atmosphere resembles that of Jupiter, with a similar pattern of light and dark bands. The clouds consist of crystals of ammonia, water, and ammonium hydrosulfide.

There are strong winds and occasional storms that last for months on Earth. Equatorial winds on Saturn can reach 500 m / s.

Summary of the main physical characteristics of the planet

-Mass: 5.69 x 10 ²⁶ kg.

-Equatorial radius: 6.0 x 10 ⁴ km

-Polar radius: 5.4 x 10 ⁴ km

-Shape: flattened.

-Average distance to the Sun: 1.4 x 10 ⁹ km

- Inclination of the orbit: 2.5º with respect to the ecliptic.

-Temperature: between -139 and -189 ºC.

-Gravity: 10.4 m / s ²

-Own magnetic field: Yes.

-Atmosphere: Yes, mostly hydrogen.

-Density: 687 kg / m ³

-Satellites: 82 formally designated, many other tiny moons, no designation.

-Rings: Yes, a complex system.

The rings of Saturn

Saturn's ring system is unique in the solar system for its extraordinary beauty. Source: Pixabay.

The rings are the hallmark of Saturn, because although the other gas giants also possess them, without a doubt those of this planet are the most spectacular.

The rings are composed mainly of ice and rocks and are kept in shape thanks to the gravitational action of some specialized satellites: shepherd satellites.

Illustration of Saturn's rings

At first, due to lack of resolution in their telescopes, astronomers thought that the rings formed a continuous disk of matter around the planet. In any case, the thickness of the system is negligible, at most, barely a kilometer, and may be meters in some regions.

The Italian astronomer Giovanni Cassini was the first to notice the existence of a dividing line between them, around 1675.

Years later, the French mathematician Pierre de Laplace pointed out that there were actually numerous thin rings. Finally, James Clerk Maxwell built a model in which he proposed that the rings were made up of many particles, each one following an independent orbit.

Astronomers distinguish rings with letters of the alphabet. The 7 main and brightest rings are A, B, C, and D, while E, F, and G are paler.

There are also thousands of weaker rings. The palest and outermost one was detected with an infrared telescope and is called Phoebe's ring.

Artist's rendering showing the rings of Saturn and the larger satellites. Source: photojournal.jpl.nasa.gov.

Cassini's division separates ring A from ring B, but in the same ring A there is a dark region called the Encke division, maintained by one of Saturn's satellites: Pan. Within the region there is also an extremely thin ring.

There are divisions of varying widths, also named after famous astronomers: Colombo, Huygens, Maxwell, and Keeler.

Origin of the rings

The rings are made up of particles ranging in size from a grain of sand (microns) to huge rocks tens of meters long, but astronomers agree that they did not originate at the same time as the planet, but very recently.

The main rings A, B and C are estimated to be probably a few hundred million years old, and that's very little in astronomical terms. Scientists are sure that all the planets in the solar system formed at the same time, about 4.6 billion years ago.

The material that makes up the rings could have come from a comet, a meteor or a moon, fragmented due to the planet's gravity. In any case, it is not the remains of the planet's formation.

Certainly the origin of the rings is uncertain at the moment, but the general consensus is that they are rather unstable, so as quickly as they formed, they may disappear over the course of a few million years.

Translation movement

Orbit of Saturn. The average distance between Saturn and the Sun is more than 1,400,000,000 km (9 AU). With an average orbital speed of 9.69 km / s, Saturn needs 10,759 Earth days to go around the Sun. Source: Todd K. Timberlake author of Easy Java Simulation = Francisco Esquembre / CC BY-SA (https://creativecommons.org/licenses /by-sa/3.0)

Saturn takes 29 years and 167 days to travel its orbit around the Sun. Curiously, Saturn and Jupiter are in orbital resonance, since there is gravitational interaction between them. Of course the attraction of the Sun is much greater, but that of Jupiter also influences.

When there is orbital resonance between astronomical objects, their orbital periods maintain a certain proportion, always with small numbers. In the case of Saturn-Jupiter, the latter rotates 5 turns for every 2 turns of Saturn and this resonance is considered to have stabilizing effects for the orbits of both planets.

The orbital resonance that occurs between the particles that make up Saturn's rings and the satellites that orbit between them, exerts a powerful effect on the structure of the rings, for example the existence of the Cassini split.

Saturn is the planet in the solar system with the largest number of satellites, 6 of them have related orbital periods, let's see:

-Mimas and Tethys, in a 1: 2 ratio. For 1 turn of Mimas, Tethys turns 2 times.

-Encélado and Dione, in relation 1: 2.

-Hyperion and Titan, in a 4: 3 ratio.

Finally, it is remarkable that 85% of the angular momentum of the solar system is concentrated in Jupiter and Saturn, the two largest planets, in contrast to the Sun, which despite having the highest mass percentage has little angular momentum.

The angular momentum of a system is an interesting physical quantity, because it is conserved in the absence of external interactions. For a change to occur, a net torque from inside is required.

Saturn motion data

The following data briefly describe the motion of Saturn:

-Mean radius of the orbit: 1.43 x 109 km

- Inclination of the orbit: 2.5º with respect to the plane of the ecliptic

-Eccentricity: 0.056

- Average orbital speed: 9.6 km / s

- Transfer period: 29.46 years

- Rotation period: 10.66 hours

When and how to observe Saturn

The planet Saturn is considered a superior planet, since its orbit is outside the orbit of the Earth. The higher planets are Jupiter, Saturn, Uranus, and Neptune. On the contrary, the planets whose orbit is closest to the Sun are called inferior planets: Mercury and Venus.

The best time to observe a higher planet is when the Earth comes between it and the Sun. On the other hand, it is more difficult to see when it is in conjunction, being further from Earth and close to the Sun, which makes it opaque. The situation is graphically described in the following image:

Opposition and conjunction of an outer planet. Source: Maran, S. Astronomy for Dummies.

Naturally, one of the main objectives of any sky observer is to view the rings, for which a small telescope is enough. But it is necessary to take into account that sometimes the rings are on edge with respect to the Earth and therefore are invisible.

The angle at which the rings are viewed changes over 30 years, which is the time that Saturn orbits the Sun.

The next oppositions of Saturn are:

-2020: July 20

-2021: August 2

-2022: August 14

-2023: August 27

-2024: September 08

-2025: September 21

Rotatory motion

Saturn takes an average of 10.66 hours to complete one revolution on its own axis of rotation, although not all of its zones rotate at the same rate. For example, at the equator the rotation speed is 10.25 hours, while inside the planet it is approximately 10.65 hours.

This phenomenon is known as differential rotation and it is due to the fact that the planet is not solid, as we have said. Also due to its liquid-gaseous nature, the planet experiences deformation due to the rotational movement, becoming flattened at the poles.

Composition

The composition of Saturn is fundamentally the same as that of Jupiter and the other gaseous planets: hydrogen and helium, only that on Saturn the proportion of hydrogen is higher, given the low density.

Since Saturn formed in the outer region of the nebula that originated the solar system, the planet was able to grow rapidly and capture a large amount of the hydrogen and helium present in the nebula.

Due to the enormous pressures and temperatures that increase as you go deeper, the molecular hydrogen on the surface is transformed into metallic hydrogen.

Although the planet is gaseous, there is a smaller proportion of heavier elements in its core, which is at least partly rocky, such as magnesium, iron and silicon.

In addition to these elements, various types of ice abound, such as ammonia, water and methane ice, which tend to accumulate towards the center of the planet, which is at a high temperature. For this reason, the material is actually liquid, rather than gaseous.

Saturn's clouds are made up of ammonia and water ice, while in the atmosphere, in addition to these substances, acetylene, methane, propane and traces of other gases have been detected.

Internal structure

Internal and external structure of Saturn. Source: Kelvinsong / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Although dominated by hydrogen and helium, Saturn is believed to contain a rocky core in nature. During the process of formation of the planets of the solar system, gases condensed around this nucleus, in a rapid process that allowed it to grow rapidly.

The nucleus of Saturn contains, as we have said, rocks and volatile elements and compounds, surrounded by a layer of liquid hydrogen. Scientists estimate that this core is between 9 and 22 times larger than Earth: about 25,000 km in radius.

This layer of liquid hydrogen is surrounded in turn by layers of liquid hydrogen and helium, which eventually become gaseous in the outermost layers. The Frenkel line is a thermodynamic boundary that separates the gaseous fluid from the liquid.

Saturn's natural satellites

According to the most recent counts, Saturn has 82 designated satellites, and a multitude of mini moons that still lack it. This makes Saturn the planet with the most satellites to date.

Saturn's satellite system is very complex; for example, they are known to have a direct action on the rings: shepherd satellites.

In addition, there are Trojan satellites, which remain in a stable orbit at 60º ahead or behind other satellites. For example, the moons Telesto and Calypso are Trojans of Thetys, one of the major satellites of Saturn.

The main satellites of Saturn are Titan, Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus and Phoebe. These satellites have been known since before space missions, but research probes to Saturn have discovered many more.

To the left Mimas and a huge impact crater. On the right the surface of Titan. Both images come from the Cassini probe. Source: Wikimedia Commons.

The largest of all the moons of Saturn is Titan, which also has its own atmosphere and is the second largest in the entire solar system, after Ganymede, the great moon of Jupiter. Titan is even bigger than Mercury.

On the other hand Enceladus, the sixth moon of Saturn in size, is a huge snowball with a surprise: its core is covered by an ocean of hot liquid water.

Saturn and Titan, its most important satellite

A curious fact among the moons of Saturn is that there are satellites whose orbits are the same, but they manage not to collide. The most notable of these coorbital satellites are Janus and Epimetheus.

Not all the moons of Saturn are spheroidal in shape, there are many irregular satellites, generally small in size and orbits quite far from the planet.

Titan and its atmosphere

Mosaic of infrared images of Titan, taken by the Cassini probe in 2015. Source: NASA via Wikimedia Commons.

It is the largest and most important of the satellites of Saturn, visible from Earth as a small point of light, with the help of the telescope. The Dutch astronomer Christian Huygens was the first to see it around 1655 and John Herschel, already in the 19th century, called it Titan.

Its approximate density is 1.9 g / cm ³ and although it contains a rocky core, it is a world almost entirely made of ice.

Titan has a dense atmosphere dominated by nitrogen and a small percentage of methane, as well as traces of hydrocarbons. This is a remarkable rarity in the solar system, since the other satellites lack an atmosphere of their own.

It also has oceans and rainfall, but not water, but methane. The existence of this compound has been known since the middle of the 20th century, thanks to the spectroscopy carried out by the astronomer Gerard Kuiper. Later the Voyager probe confirmed this discovery.

The interesting thing about Titan is that many organic compounds have been detected there, in addition to methane, which are precursors of life. The mechanism by which Titan acquired this peculiar atmosphere is still unknown, but it is of great interest, since the abundance of hydrocarbons is much greater than that of Earth.

As part of the Cassini mission to Saturn, the Huygens probe managed to land on the surface of Titan and found a frozen surface, but full of landforms.

Although Titan enjoys a varied geology and climate, it is an unwelcoming world for humans. Its atmosphere is very dynamic; For example, high-speed winds are known to blow, far superior to the largest land-based hurricanes.

Missions to Saturn

Pioneer 11

It was launched by NASA in 1973 and reached the orbit of Saturn some years later, in 1979. This mission captured low-resolution images and also found unknown satellites and rings never seen from Earth.

The probe was finally adrift in 1995, but bearing the plaque with the famous message created by Carl Sagan and Frank Drake, in the event that alien navigators came across it.

Voyager

This mission consisted of the launch of two probes: Voyager 1 and Voyager 2.

Although Voyager 1 was conceived to reach Jupiter and Saturn, it has already exceeded the confines of the solar system, entering interstellar space in 2012. Among its most important findings is the confirmation of the existence of Titan's atmosphere, as well as important data of Saturn's atmosphere and the ring system.

Voyager 2 collected information about Saturn's atmosphere, atmospheric pressure, and numerous high-quality images. After visiting Saturn, the probe reached Uranus and Neptune, after which it entered interstellar space, as did the sister probe.

Cassini

The Cassini mission was a joint project between NASA, the European Space Agency, and the Italian Space Agency. It was launched in 1997 from Cape Canaveral and its objective was to study the planet Saturn and its satellite system.

The probe reached Saturn in 2004 and managed to orbit the planet 294 times until 2017, when it ran out of fuel. The probe was then deliberately submerged in Saturn, to prevent it from crashing into one of the satellites and thus avoid radioactive contamination.

Cassini carried the Huygens probe, the first human-made object to land on a world beyond the asteroid belt: Titan, Saturn's largest satellite.

Huygens contributed images of Titan's landscape, as well as the structure of the rings. It also obtained images of Mimas, another satellite of Saturn that grazes rings. They show the huge Herschel crater, with a huge mountain in its center.

Cassini also confirmed the presence of water on Enceladus, Saturn's sixth icy moon, 500 km in diameter, which is in orbital resonance with Dione.

Enceladus, the icy moon of Saturn that houses an ocean inside. Cassini probe image. Source: Wikimedia Commons. NASA / JPL / Space Science Institute / Public domain.

Enceladus' water is hot, and the planet is full of geysers and fumaroles that expel water vapor and organic compounds, which is why many believe that it could harbor life.

About Iapetus, another of Saturn's large satellites, Cassini images revealed a darkened side, the origin of which is still undetermined.

References

1. The sky of the month. Conjunctions and oppositions external planets. Recovered from: elcielodelmes.com.
2. Maran, S. Astronomy for Dummies.
3. POT. Cassini Missions. Recovered from: solarsystem.nasa.gov.
4. Powell, M. The Naked Eye Planets in the Night Sky (and how to identify them). Recovered from: nakedeyeplanets.com.
5. Seeds, M. 2011.The Solar System. Seventh Edition. Cengage Learning.
6. Wikipedia. Planetary ring. Recovered from: es.wikipedia.org.
7. Wikipedia. Saturn (planet). Recovered from: es.wikipedia.org.
8. Wikipedia. Saturn (planet). Recovered from: en.wikipedia.org.