We have already told you about the "giant" of our Solar System in the past, Jupiter, the largest and most massive planet of all. As we well know, however, in our cosmic neighborhood there are other celestial bodies, less large than Jupiter but equally fascinating. Today, in fact, we will deal with one of the most famous, known and characteristic worlds of our system: the lord of the rings, Saturn.
History
The observations of the planet are almost as old as our history. Saturn, in fact, is the penultimate of the planets visible to the naked eye (which are Mercury, Venus, Mars, Jupiter and Saturn) and was known since ancient times. Suffice it to say that the Romans – not surprisingly – gave the name of the planet to the god of agriculture (the equivalent of the Greek titan Cronus). It was Galileo Galilei, however, who noticed the strange shape of the Gas Giant for the first time in 1610. During the first observations the Pisa astronomer was unable to completely reconstruct the figure of the planet because of its rings, defining it composed of three bodies .
As always, however, the discovery of something is not to be connected to a single individual: it was Eustachio Divini, in 1649, to show everyone for the first time a detailed illustration of the rings of Saturn and then Christiaan Huygens, in 1655, was the first to guess the annular shape of the bodies seen by Galileo around the planet.
Giovanni Cassini, however, in 1675 was the first to hypothesize the nature of its main feature, the rings. The discoveries then followed and, even now, the planet is constantly being studied by scientists.
Curiosity
Saturn "lives" between Jupiter and Uranus and is the sixth celestial body of the Solar System. After Jupiter, it is the largest planet and its distance from the Sun is about nine times greater than that of Earth (one billion 429 million kilometers). The gas giant takes a long time to go around our star: 29 and a half years. Compared to Earth, it is 10 times larger in diameter and 700 times larger in volume; due to the low density (the lowest, by far, among the planets of the Solar System), however, its mass is "only" 95 times that of our planet. Saturn is a gaseous planet and is the only one in our galactic district that has an average density lower than that of water (687 kilograms per cubic meter, against 1,000 of liquid water).
For this reason, if it were possible to immerse the world in an immense ocean of water, the planet would float.
Saturn is made up (like Jupiter) mainly of hydrogen and helium, and has a complex structure, the material of which becomes progressively denser proceeding towards the inner part of the planet; however, the division between the different layers is not well defined.
The nucleus is probably small in size, dense and rocky in nature, with a composition similar to that of Earth. Here the gravitational compression of the planet produces very high pressures and temperatures that reach 12,000 ° C. The great heat generated by the core is the cause of the convective currents in the outermost fluid layers.
The atmosphere is very turbulent, with winds moved by the internal heat of the planet (and not by the Sun as it happens on Earth) that blow up to 1,800 km / h; at high latitudes there are also cyclones with a relatively short duration which also extend for 1,200 kilometers.
In the 1980s the two probes of the Voyager program photographed a hexagonal structure present near the north pole of the planet; structure observed later also by the Cassini probe.
Each side of the hexagon measures approximately 13,800 kilometers. The causes of the presence of this regular geometric shape are not yet known, but there seems to be no connection with Saturn's radio emission and its polar aurora activity.
The most famous structures instead, the rings, are composed of millions of small icy objects, the size that varies from micrometer to meter, orbiting around the planet on its equatorial plane. The origin of the rings is unknown. There are two main hypotheses in this regard: that they are the result of the destruction of a satellite of Saturn, caused by a collision with a comet or with another satellite, or that they are a "surplus" of the material from which Saturn was formed which is not managed to assemble into a single body.
Satellites
Saturn possesses a high number of natural satellites, 82, some discovered recently, and which have removed the title of "Lord of the satellites" from Jupiter. Many of the moons are rather small: 34 of them have a diameter less than 10 kilometers. Particularly noteworthy moons of Saturn are Titan, the second largest moon in the solar system, with a rich nitrogen atmosphere and a landscape with hydrocarbon lakes and dry river networks, and Enceladus, which could contain liquid water in the subsoil of its south pole region.
Titan is considered similar to the primordial Earth, but with a much lower temperature, where the methane cycle replaces the hydrological cycle present on our planet instead.
Just like our beautiful world, the climate, which includes wind and rain (always with methane), has created surface characteristics similar to those found on Earth, such as dunes, rivers, lakes and seas (there are even seasons).
Enceladus, on the other hand, is one of the three celestial bodies of the external solar system where active eruptions have been observed. Analyzes of the emitted gases suggest that they were generated from liquid water located below the surface. Together with the chemical analyzes of the plume, these discoveries have fueled the hypothesis that Enceladus is an important subject of study in the field of exobiology.
Missions, past and future
The Pioneer 11 it was the first space probe to perform a close flight of Saturn in September 1979, when it passed 20,000 kilometers from the top of the planet's clouds. Images of the planet and some of its moons were taken, although the low resolution made it impossible to detect details of the surface. The probe Voyager 1 he visited the Saturn system in November 1980, sending the first high resolution images of the planet, its rings and the main moons, also making a flyby with Titan, increasing the knowledge of its atmosphere. In August 1981, almost a year later, the Voyager 2 the study of the Saturn system continued. He acquired several other close-up pictures of the planet's moons, showing evidence of some changes in the atmosphere and rings.
The most important probe to have explored the gas giant is the Cassini-Huygens, which entered into orbit around Saturn on 1 July 2004, with the aim of studying the Saturnian system and subsequently sending a lander on the mysterious surface of Titan, hitherto unknown due to the thick atmospheric blanket that envelops the main moon of Saturn.
After discovering eight new satellites (and much more), Cassini's main mission ended in 2008, however, it was first extended until 2010 and subsequently extended until 2017.
Among future missions, however, NASA plans to explore the two main (and most famous satellites on the planet). The possible mission that Titan will explore, called Dragonfly, will be a drone sent for study prebiotic chemistry and the possibility of existence of extraterrestrial life in environments other than Earth. The vehicle will be able to visit different areas of the surface thanks to the ability to move in flight.
The American space agency also plans to explore Enceladus, the most likely place to find extraterrestrial life. However, for these missions we should wait a little longer, in the meantime, just as the men who made the discoveries on the planet did in the 1600s, we just have to do one thing: dream.
