Saturn

Average distance from the Sun (semi-major axis):	1.433 billions of km
Minimum distance from the Sun (perihelion):	1.352 billions of km
Maximum distance from the Sun (aphelion):	1.515 billions of km
Revolution period around the Sun (Saturnian Year):	29.45 Earth years
Inclination of the Orbit (respect to the plane of the Earth's orbit):	2.5°
Equatorial Diameter:	120,536 km
Polar Diameter:	108,728 km
Mass:	5.7 x 1026 kg (95 times the Earth's mass)
Rotation Period (equator):	10 hours 33 min
Medium surface temperature (top atmosphere):	93 K (-180 °C)

This page presents some images of Saturn taken by the author in the overall arc eighteen years old, from 2001 to 2019. The basic instrumentation used was almost always the same: a Schmidt-Cassegrain telescope with a diameter of 200mm and a focal length of 2 meters on a motorized equatorial mount. Instead, over time, the camera instrumentation has evolved as well as the techniques of acquisition and processing of images, trying to improve the final quality.
However, it is not possible to disregard even short but necessary comments and explanatory notes, for the purpose of also accompany the less experienced reader towards a greater understanding of the images themselves and, in general, of the physical reality enclosed in them.

Saturn is known as the "planet of the rings" and by someone also referred to as the "Lord of the Rings", title freely borrowed from a successful series of books and films of the fantasy genre.
The planet is, in effect, surrounded at the equator, by a series of concentric rings which they start at a distance of 6,600 km from the top of Saturn's atmosphere clouds and extend up to a distance of 120,000 km. Galileo Galilei was the first to observe Saturn through a telescope but the poor quality of his lenses tool did not allow him to identify them for what they were. After a few years, with the construction of better telescopes, the rings were clearly visible but their true nature was understood only much later: a set of small particles, mainly ice, that orbit in a manner solidary but independent around Saturn; the overall effect is that of concentric rings.
In the course of its orbit around the Sun, lasting almost thirty Earth years, the inclination of Saturn as it is seen from the Earth changes and, consequently, also changes the angle with which we see the rings: every 14.8 years, for example, these are cut and become almost invisible to the terrestrial observer; vice versa, in intermediate periods they show themselves in all their fascinating splendor, as some of the photos of the author presented below can unworthily demonstrate.

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Saturn Images

October 28 2001, 22:08 UT

February 7 2011, 00:27 UT

February 25 2012, 01:39 UT

May 13 2014, 19:55 UT

May 5 2015, 22:29 UT

May 21 2016, 21:55 UT

June 16 2017, 21:12 UT

July 5 2017, 19:38 UT

June 1 2018, 22:54 UT

July 12 2018, 20:18 UT

July 12 2019, 21:03 UT

July 22 2019, 20:23 UT

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Missions to Saturn

The first ever mission to Saturn was that of Pioneer 11 in 1979. The probe passed 21,000 km from the top layer of clouds on the planet and resumed the first ever close-up images of this world and its ring system.

A year after the passage of Pioneer 11, the Voyager 1 reaches the planet of the rings to make its close passage and try to steal as many secrets as possible. Only one year later, in 1981, even the twin probe Voyager 2 comes close to Saturn. In both cases it is once again a case of one approach mission, there are no stops in orbit around Saturn; the probes already had visited Jupiter previous but after Saturn their destinies will separate forever: both destined to wandering in the deep interstellar spaces for hundreds of thousands and, perhaps, millions of years, Voyager 2 will have two more appointments first; Uranus and Neptune.
The instrumentation on board is much better and more sophisticated than that of the Pioneer, so the data transmitted to the Earth are much more complete and in-depth; even the on-board cameras are more advanced and the images that the probe transmits are impressive.

The details taken from Voyager 1 of the atmosphere of Saturn show a breathtaking view, with colors hardly imaginable. In the highest part of the atmosphere there are clouds of crystals of ammonia, lower than ammonium hydrosulphide and water; methane, propane, acetylene and other hydrocarbons are also present. The planet is actually composed mostly of hydrogen and a much smaller part of helium; advancing towards the interior of Saturn the ever increasing atmospheric pressure transforms hydrogen from gas to a liquid state, up to the central areas where it becomes metallic. The core of the planet should be rocky and about 25,000 km in diameter.

Saturn, like Jupiter, emits more energy than it receives from the Sun especially in the infrared wavelengths. While for Jupiter the cause is fully attributable to the mechanism gravitational contraction that compensates hydrostatic pressure (known as Kelvin-Helmholtz mechanism), for Saturn does not seem sufficient to explain all the re-emitted energy. It has been suggested that an important contribution to the planet's energy balance may be carried by the heat generated by helium drops which, from the atmosphere above, rain on the layers of more internal and dense hydrogen; condensing for high pressure helium drops produce heat which would then escape to the outside.

Extraordinary image of the Rings of Saturn in false colors taken from the Voyager probes.

Dione, one of Saturn's moons with a large amount of impact craters. Approximate distance from Saturn 377,000 km has a diameter of about 1,100 km.

Mimas with a diameter of 415 km orbits around Saturn at an average distance of 185,000 km in 22 hours and 37 minutes. The colossal impact crater visible in the photo was named Herschel, from the name of the discoverer of Mimas. The crater has a diameter of 140 km, that is one third of the total diameter of the moon, its edges are almost 5 km high and, in some areas within it, are found depressions that can reach 10 km of depth compared to the surrounding surface.
Voyager 1 photographed this moon in 1980, only three years after the release of the Star Wars movie in theaters; the similarity of the aspect of this satellite with the famous Death Star of the movie unleashed the people imagination.

After the first pioneering missions of the seventies of the twentieth century with the probe Pioneer 11 before and the twins Voyager 1 Voyager 1 and Voyager 2 later, we had to wait until the beginning the first years of 2000 to have a new mission on Saturn. The probe Cassini after a journey of three and a half billion kilometers and lasting seven years arrives on 1 July 2004 in orbit around the planet of the rings. This time it is not a simple "flyby" but a real long-term and mission-depth exploration, with the aim to learn as much as possible both on the planet and its moons, especially the most' great Titan that has long attracted the attention of astronomers, physicists and biologists.
The mission, which was initially planned for a stay of four years in the Saturnian system, was extended for another seven, and later, continued until 2017, for the excellent conditions of the space probe, the amount of discoveries made and the enormous amount of data collected.
On 26 April 2017 the Cassini was put into a series of orbits that would have led it to progressively get closer to Saturn, until it burns in its atmosphere: this is to analyze in loco the characteristics of the saturnian atmosphere and to avoid that any terrestrial bacteria present on probe could "infect", in some way, one of the moons. This last phase of the mission, called Grand Final ended September 15, 2017 after twenty-two "dives" between the rings of Saturn and the planet.

The discoveries made by Cassini on Saturn have been many and extremely important. First of all concerning the planet with the observation of storm unions, aurora on the night side and measurements of the magnetic field; most of all, however, the observation of the colossal hexagonal storm covering the northern polar cap.
Seen false color images, the storm appears truly fascinating and, at its center, clearly distinguishes an area that recalls a cyclonic formation of an intense red color, like a kind of rose in the center of the hexagon; the overall effect is something kaleidoscopic and psychedelic.
The reason why the storm is hexagonal in shape is still not clear, it is probably tied in some way to the radio emissions of Saturn and with the activity connected to the polar auroras; it sure is that it is a unique structure throughout the Solar System.

Saturn's atmosphere is full of other surprises with spectacular, intensely colored panoramas as shown by the following photo of the planet's atmosphere elaborated in false colors by an amateur astronomer.

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The spectacular rings have been repeatedly photographed and studied by Cassini, with images that have revealed complex and wonderful structures
Divided into seven main bands, each separated by almost empty spaces, the rings are composed in mostly from ice particles, with larger fragments that can reach a size about ten meters; the total thickness of the rings should not exceed one kilometer.
The divisions between the bands are probably due to gravitational resonance effects with some small moons that orbit the planet, some well within the ring system: these moons, called shepherd satellites, they helped shape the current structure of the rings.
The bands, also improperly called "Rings", are identified with the letters of the alphabet and in order of discovery, for which we start from Ring A up to Ring D closer to the planet, then the Ring E very external and weak, to then find the subtle Ring F with its shepherd satellites Prometheus and Pandora just outside of Ring A, to end with the Ring G even more external than F but much closer to Saturn of the large E.
In 2009 a new ring was discovered, called Phoebe's Ring as it is found right on the orbit of this satellite. It is a weak link and very far from Saturn, in that it starts at about six million km from the planet and extends to a distance of almost twelve million of km; it is absolutely the largest ring and appears to consist of fine particles of dust and ice and is visible only in the infrared. His discovery could explain the strange coloring observed on another Saturn satellite: Iapetus; the satellite in fact crosses the ring during the its orbit and the particles collide and settle on it.

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Saturn is by far the planet with the most known satelli: as many as 82 from the last data of October 2019; it then surpasses Jupiter who has "only" 79. Most of these moons are small pieces of rock captured by the planet's gravitational attraction, they may originally have been asteroids wanderers in the Solar System; some of them, instead, are real worlds that Cassini has literally revealed, with amazing discoveries that pose further questions even more intriguing.

The small moon Metone, discovered by Cassini on his journey towards the orbit of Saturn.

The moon Phoebe, photographed by the Cassini probe shortly before arriving in orbit around Saturn. From this satellite, with its very irregular shape, it seems that the material that created the namesake ring is generated from it.

Tethys photographed with the background of the rings. With a diameter of just over a thousand km it is composed mainly water ice, like Saturn's rings.

The heterogeneous surface of the satellite Dione, in which structures created by tectonic movements coexist with those from meteor impact. Both testify to the tormented past of the moon: subjected to intense bombardment by asteroids and site of intense internal activity, which has created fractures and faults in the crust.
With a diameter of just over 1,100 km, this moon reveals, surprisingly, a complex geological "puzzle". The smallest detail perceptible in the photo has a size of about 660 meters.

Epimetheus here photographed by Cassini with Saturn in the background from a distance of about 2,700 km. The diameter of this moon is only 113 km, therefore it could not have had, in its geological history, any type of endogenous activity; in fact the only visible features on the surface are the impact craters of smaller asteroid bodies that have collided with the satellite million or billions of years ago. The resolution of this photo is 160 meters per pixel.

Mimas taken up as it stands out against the background of the rings from which, however, it is almost 45,000 km away. This satellite has contributed, it is thought in a relevant way, to create what is called Cassini Division, which is the empty space between rings A and B which has an extension of almost 5,000 km. At the time of the photo Mimas was 183,000 km away and the resolution is 1 km per pixel.

This photo is a clear demonstration of how even the smallest satellites of Saturn can heavily affect the structure and appearance of the rings. The small moon Pan, of the diameter of only 28 km, not only created an empty space in the ring system (called Division of Encke) but has also influenced their structure in many distant areas, with gravitational effects which manifest themselves as waves of orbital resonance. These waves are visible as groupings close to clear areas, high density of particles, with dark ones that are almost devoid of them.

Already from the Voyager missions had guessed that the small satellite Enceladus could hide some surprises, however nobody could really imagine that a body with a diameter of slightly less than 500 km orbiting at 238,000 km from Saturn and with an average surface temperature of -200 ° C it results a credible candidate for hosting life forms.

The Cassini brought the first tangible evidence of the internal activity that takes place on this small moon, photographing huge plumes of material expelled from geysers positioned at the south pole. The ejected material is mainly formed by water vapor that goes to supply the E ring that lies along the orbit of Enceladus; the presence of water vapor means that there is an energy source inside the moon, capable of maintaining a large pocket of liquid water beneath the crust icy. The energy source could be a combination of tidal forces due to gravity of Saturn and orbital resonance with another moon, Dione, plus the action of radioactive elements inside the satellite.
Furthermore, Cassini also managed to cross one of these jets of water vapor as it came expelled from Enceladus and detected traces of organic substances, so it is thought that in the ocean hidden under 40 km of icy crust of the south pole of the satellite and 8 km deep, the conditions can be suitable for the formation of life, even if in its simplest forms.

Split of the internal structure of Enceladus according to the most recent theories and based on the data of the Cassini probe. From the hydrothermal vents on the ocean floor comes the primary heat source that it makes possible the existence of water in the liquid state, they also provide for the supply of substances that could be used by microorganisms to feed them.

The spectacle of the sky seen by Enceladus would be truly extraordinary: Saturn with apparent dimensions of 30° would dominate the view, always fixed in the sky and showing phases. The rings would appear almost cutting, casting shadows on the planet's disk. Mimas would pass on the Saturn disk every 72 hours and would have almost the same size as our Moon seen from Earth. Under this sky, in proximity of the south pole, huge geysers or cryovolcaneos they would erupt water vapor and icy water crystals in space; the saltiest particles they would fall on the surface while the others would feed the Ring E around Saturn.

Titan is the largest of Saturn's moons, with a diameter of 5,150 km and orbit at a verage distance from the planet of 1,222,000 km. It was the object that aroused most curiosity among scientists, however away of its dense atmosphere that did not make its surface details be seen and that seemed composed mainly from hydrocarbons: a panorama that seemed to remember that of the primordial Earth, before that living organisms begin to produce oxygen and change the appearance of our planet.
The space probe Piooner 11 first and the Voyager 1 shortly after, in the early eighties of the last century, tried to take pictures of Titan but the one obtained on only photos of the its dense and foggy atmosphere.

The real turning point came with the Cassini mission, when in 2004 the probe approached Titan and, thank to its radar mapping equipment, sent us the first images of the surface, "piercing" the layer of clouds. Combining the radar mapping data with those derived from the physics and chemistry analyzes performed on the satellite by the numerous scientific instruments on board the probe, it was possible to construct a scenario that is in no way inferior to the wildest fantasies of the most fervent science fiction writers.

Lakes as large as seas, of methane in the liquid state, with methane rains and other hydrocarbons that feed; all dominated by a dense and heavy atmosphere of nitrogen and methane with winds that can get to blow at 120 km per hour. The surface temperature is around -179 ° C however this does not prevent scientists from thinking that perhaps some exotic form of life, based on methane instead of on water as on Earth, may exist in such an environment. Rain would bring on the surface too acetylene which could be the favorite food of these strange and hypothetical titanian organisms. Below all this, hidden in the depths of Titan under a crust of ice, an ocean of water and ammonia.

The Cassini probe, however, had a rather special "passenger" on board: the descent module Huygens, intended for direct exploration of the surface of Titan. Scientists had been indeed far-sighted and, thanks to an agreement between NASA (American Space Agency) and ESA (European Space Agency) was also built the small probe Huygens , destined to explore what already in the eighties of the twentieth century promised to be a full world of hidden wonders: Titan. Mounted on the Cassini, they faced together the long journey towards Saturn, until December 23rd 2004, when the two small spaceships separate forever. After another twenty days of travel and four million kilometers traveled, the Huygens came into contact with the atmosphere of Titan and it began to send to Earth the first close-up images of the surface, thanks to which it was also possible to see rivers and related tributaries of hydrocarbons which then flow into the large ones methane lakes or seas. Taking advantage of the atmosphere to slow down its speed, thanks to a heat shield specially designed, and opening a parachute the little terrestrial explorer was about to land on this strange and new world, continuing to transmit images and scientific data.

The descent into the atmosphere of Titan lasted about two hours and the Huygens, once landed, succeeded to broadcast for another hour and a half; at least until the batteries of the small descent module didn't run out.
Here alongside one of the images transmitted directly from the surface: a panorama that, to a first and superficial examination does not appear dissimilar to that of Mars as shown by the numerous probes of exploration sent on the red planet. However, by analyzing them better, there are differences substantial: first of all, when the probe landed, at 12:43 UTC on 14 January 2005, it raised a a small cloud of dust that turned out to be instead a sort of organic aerosol; there surface then it is a mixture of water ice in granular form, which resembles sand. The ground temperature was -179 ° C and atmospheric pressure equal to one and a half times that terrestrial: in its composition it has been found a percentage of methane equal to approximately 5% and the area landing was free of fog, due to the low relative humidity. The "stones" that you see in the photos should actually be made of water ice covered with a layer of hydrocarbons icy. In essence the Huygens landed in a substantially "desert" area not far away from some "oases" fed by aquifers. The shaped appearance of the "stones" implies that they were subjected to an action by fluids, moreover the absence of pebbles smaller than 5 cm testifies that these were taken away by a current up to the lakes, while the larger ones did not move: probably this desert area was previously a bed of a stream now dried up. Thanks to other information transmitted by Huygens, the atmosphere was established manages to conserve a large amount of water coming from the sun's evoporation, however this process is rather slow, as only a few centimeters of water each year succeed in evaporate from the cold soil of Titan, due to the distance of the Sun and the surrounding mists Titan that significantly weaken the action of sunlight. In practice, Titan is subject to sudden and violent torrential rains interspersed with decades of drought.
The light on Titan, even when the Sun is high in the sky, never exceeds the perennial twilight.

In the near future it will perhaps be possible to see another probe flying towards Saturn, but this time designed specifically to explore its moon Titan even more directly and thorough compared to the past. The mission Dragonfly aims to bring a flying drone to Saturn's satellite so it can explore different sites and look for evidence of the existence of life.
Below is a short video animation illustrating how the probe will operate on Titan.

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