Saturn (planet)
Saturn is the sixth planet in the solar system from the Sun, the second in size and mass after Jupiter, and the only one with a ring system visible from Earth. Its name comes from the Roman god Saturn. It is part of the so-called outer or gaseous planets. The most characteristic aspect of Saturn is its bright and large rings. Before the invention of the telescope, Saturn was the farthest of the known planets and, to the naked eye, did not appear bright or interesting. The first to observe the rings was Galileo in 1610, but the low inclination of the rings and the low resolution of his telescope made him think at first that they were large moons. Christiaan Huygens, with better means of observation, was able to clearly observe the rings in 1659. James Clerk Maxwell, in 1859, proved mathematically that the rings could not be a single solid object but must be the grouping of millions of smaller particles. The particles that make up Saturn's rings rotate at a speed of 48,000 km /h, 15 times faster than a bullet.
Origin of the name of the planet Saturn
Because of its orbital position farther away than Jupiter, the ancient Romans gave the name of the father of Jupiter to the planet Saturn. In Roman mythology, Saturn was the equivalent of the ancient Greek Titan Cronus, son of Uranus and Gaea, who ruled the world of gods and men, devouring his children as soon as they were born so that they would not dethrone him. Zeus, one of them, managed to avoid this fate and finally overthrew his father to become the supreme god.
The Greeks and Romans, heirs of the Sumerians in their knowledge of the sky, had established the number of stars that moved in the firmament at seven: the Sun, the Moon, and the planets Mercury, Venus, Mars, Jupiter and Saturn, the "wandering" stars that, at different speeds, orbited around the Earth, center of the universe. Of the five planets, Saturn is the slowest moving, it takes about thirty years (29,457 years) to complete its orbit, almost triple that of Jupiter (11,862 years) and with respect to Mercury, Venus and Mars the difference is much greater. Saturn stood out for his slowness and if Jupiter was Zeus, Saturn had to be Cronus, the old father, who wanders step by step among the stars.
General characteristics
Saturn is a planet visibly flattened at the poles with a protruding equator forming an oval spheroid. The equatorial and polar diameters are 120,536 and 108,728 km, respectively. This effect is produced by the planet's rapid rotation, its fluid nature and its relatively low gravity. The other giant planets are also oval but to a lesser extent. Saturn has a specific density of approximately 690 kg/m³, making it the only planet in the solar system with a density less than that of water (1000 kg/m³). The planet's atmosphere is made up of 96% hydrogen and 3% helium. The planet's volume is enough to contain 740 times the Earth, but its mass is only 95 times the Earth's, due to the aforementioned low medium density.
Saturn's period of rotation is uncertain since it has no surface and its atmosphere rotates with a different period at each latitude. Since Voyager times, Saturn's rotation period, based on the periodicity of radio signals emitted by it, was considered to be 10 h 39 min 22.4 s (810.8°/day). The Ulysses and Cassini space missions have shown that this period of radio emission varies in time, currently being 10 h 45 min 45 s (±36 s). The cause of this change in the period of radio rotation could be related to cryovolcanic activity in the form of geysers from the satellite Enceladus, which releases material in orbit of Saturn capable of interacting with the external magnetic field of the planet, used to measure the rotation of the inner core where it is generated. In general, it is considered that the internal rotation period of the planet can only be known approximately.
Compared to planet Earth, Saturn is nine times larger, and its orbit is nine times farther from the Sun. This means that if we look at Earth and Saturn from the Sun when they are at the same point, at an intersection node of their orbits, Earth has the same apparent size as Saturn.
Internal structure
Typical planetary models consider the interior of the planet to be similar to that of Jupiter, with a rocky core surrounded by hydrogen, helium, and traces of other volatiles. Above it lies an extensive layer of liquid hydrogen, due to the effects of high pressures and temperatures. The outer 30,000 km of the planet are made up of a vast atmosphere of hydrogen and helium. The interior of the planet probably contains a core made up of icy materials accumulated in the early formation of the planet and which are in a liquid state at the pressure and temperature conditions near the core. It is found at temperatures around 12,000 K—about twice the temperature of the Sun's surface.
On the other hand, and like Jupiter and Neptune, Saturn radiates more heat to the outside than it receives from the Sun. A part of this energy is produced by a slow contraction of the planet that releases the gravitational potential energy produced in the compression. This mechanism is called the Kelvin-Helmholtz mechanism. The extra heat generated is produced in a phase separation between the relatively homogeneous hydrogen and helium that have been differentiating since the formation of the planet, releasing gravitational energy in the form of heat.
Atmosphere
Saturn's atmosphere has a pattern of dark bands and light patches similar to Jupiter's, although the distinction between the two is much less clear for Saturn. The planet's atmosphere has strong winds in the direction of alternating parallels in latitude and highly symmetrical in both hemispheres despite the seasonal effect of the planet's axial tilt. The wind is dominated by a strong and broad cloud-height equatorial current that reached speeds of up to 450 m/s in Voyager times. Unlike Jupiter, no large stable vortices are apparent, although smaller ones do exist.
The upper clouds are likely to be made up of ammonia crystals. Above them seems to spread a uniform fog over the entire planet, produced by photochemical phenomena in the upper atmosphere - around 10 mbar. At deeper levels—around 10 bar pressure—water in the atmosphere could condense into a layer of water clouds that has not yet been observed.
As on Jupiter, storms occasionally form in Saturn's atmosphere, some of which have been observed from Earth. In 1933, a white spot located in the equatorial zone was observed by the amateur astronomer W. T. Hay. It was large enough to be visible in a 7cm refractor, but it soon dissipated and vanished. In 1962, a new stain began to develop, but it never came to prominence. In 1990, a gigantic white cloud could be observed at Saturn's equator that has been assimilated to a process of formation of great storms. Similar spots have been observed on photographic plates taken over the last century and a half at intervals of about 30 years. In 1994, a second large storm could be observed, approximately half the size of the one produced in 1990.
The Cassini probe has been able to capture several large storms on Saturn. One of the largest storms, with lightning 10,000 times more powerful than any storm on Earth, appeared on November 27, 2007, having lasted 7 and a half months — for a time the record for the duration of a storm in the solar system. This storm appeared in the southern hemisphere of Saturn, in an area known as "storm alley" due to the high frequency with which these phenomena appear there. This record, however, has been beaten by another storm that appeared in the same area, which was detected in January 2009 and lasted until October of that year.
A huge storm, so large that it encircled the planet, appeared in December 2010 in Saturn's northern hemisphere developing a 5,000-kilometre-wide dark-colored central vortex similar to Jupiter's Great Red Spot, being just as powerful — far more than any terrestrial storm — that dragged clouds of ammonia crystals from deep in the planet's atmosphere. During the approximately 200 days that it lasted, it was studied with the help of the Cassini probe and terrestrial telescopes, it grew and expanded until it reached an area eight times the size of the Earth, and the radio waves produced by the electrical apparatus could be captured. associated with her.
The polar regions present jet streams at 78° N and 78° S. The Voyager probes detected in the 1980s a hexagonal pattern in the north polar region that has also been observed by the Hubble Space Telescope during the 1990s. The most recent images obtained by the Cassini probe have shown the polar vortex in great detail. Saturn is the only planet known to have such a polar vortex, although polar vortices are common in the atmospheres of Earth or Venus.
In the case of Saturn's hexagon, the sides are about 13,800 kilometers long —slightly more than the diameter of Earth— and the structure rotates with a period identical to that of the planetary rotation, being a standing wave that does not change its length or structure, as do the rest of the clouds in the atmosphere. These polygonal shapes between three and six sides have been replicated by rotating fluid models on a laboratory scale.
Unlike the north pole, images of the south pole show the presence of a jet stream, but no vortices or persistent hexagonal waves. However, NASA reported in November 2006 that the Cassini spacecraft had observed a hurricane at the south pole, with a well-defined eye. Well-defined storm eyes had only been observed on Earth—not even been observed. managed to observe it in the Great Red Spot of Jupiter by the Galileo probe. This vortex, approximately 8,000 kilometers in diameter, has been photographed and studied in great detail by the Cassini probe, measuring winds of more than 500 km/h.
In April 2010, NASA released some videos and images in which you can see the electrical equipment associated with storms that occur in Saturn's atmosphere, the first time this has been achieved.
Orbit
Saturn revolves around the Sun at an average distance of 1,418 million kilometers in an orbit with an eccentricity of 0.056, which places aphelion at 1,500 million kilometers and perihelion at 1,240 million kilometers. Saturn had its last perihelions in 1974 and in 2003. The period of revolution around the Sun is 29 years and 167 days and the period of rotation on its axis is short, 10 hours and 14 minutes, with some variations between the equator and the poles.
Its synodic period is 378 days, so that, each year, the opposition occurs almost two weeks later than the previous year. Seen from Earth, Saturn's apparent motion relative to the background stars is direct except near opposition. Saturn will appear to go retrograde about 69 days before opposition and will remain so for a period of about 138 days, apparently moving “backward” through an angle of 6.8° before returning to motion. straight.
Saturn's orbital elements are modified on a scale of ~900 years due to a 5:2 orbital resonance with the planet Jupiter, a resonance named by French astronomers of the XVIII as la grande inégalité(Jupiter completes approximately 5 turns for every 2 of Saturn). The planets are not in perfect resonance, but they are close enough to it that perturbations in their respective orbits are appreciable.
Satellites
Saturn has a large number of satellites (82 with regular orbits, as of 2019) the largest of which, Titan, is the only satellite in the solar system with a significant atmosphere.
The largest satellites known before the start of space research are: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus and Phoebe. Both Enceladus and Titan are particularly interesting objects for planetary scientists, since the former believes the possible existence of liquid water at a shallow depth of its surface, based on the emission of water vapor in geysers, and the latter, It presents an atmosphere rich in methane and similar to that of the primitive Earth.
Another 30 satellites of Saturn have names, but the exact number is uncertain because there are a large number of objects that orbit this planet. In the year 2000, 12 new satellites were detected, whose orbits suggest that they are fragments of larger objects captured by Saturn. The Cassini-Huygens mission has also found new satellites, the last of which was announced on March 3, 2009, making it the planet's 61st.
Titan's apparent disk—a fuzzy orange circle with slightly darker edges—can be seen with amateur telescopes starting at 200mm aperture, using more than 300 magnification and stable skies: in its closest approaches it reaches to measure 0.88 seconds of arc. The rest of the satellites are much smaller and always look like stars, even at high magnification.
The innermost satellites can be captured, however, with any CCD camera using focal lengths greater than 2 m.
Ring system
Saturn's most notable feature is its rings, which greatly perplexed early observers, including Galileo. His telescope was not powerful enough to reveal the true nature of what he was observing, and due to an error in perspective, he believed that they were two independent bodies flanking the planet. A few years later, Saturn presented the rings in profile, and Galileo He was very surprised by the abrupt disappearance of the two hypothetical companions of the planet. Finally, the existence of the ring system was determined by Christiaan Huygens in 1659, with the help of a more powerful telescope.
Saturn's rings extend in the planet's equatorial plane from 6,630 km to 120,700 km above Saturn's equator and are composed of particles with abundant water ice. The size of each of the particles ranges from microscopic dust particles to rocks a few meters in size. The high albedo of the rings shows that they are relatively early in the history of the solar system. Saturn's rings were originally thought to be unstable over periods of tens of millions of years, another hint of their recent origin, but data sent back by Cassini suggests they are much older than previously thought. at first. Saturn's rings have a very complex orbital dynamics presenting density waves, and interactions with Saturn's satellites (especially with the so-called shepherd satellites). Being inside the Roche limit, the rings cannot evolve towards the formation of a larger body.
The rings are distributed in areas of higher and lower material density, with clear divisions between these regions. The main rings are the so-called A and B rings, separated from each other by the Cassini division. In the region inside ring B, another fainter but extensive ring can be distinguished: C and another faint and fine ring: D. On the outside you can distinguish a thin and weak ring called the F ring. The faint ring E extends from Mimas to Rhea and reaches its greatest density at the distance of Enceladus, which is thought to provide it with particles due to emissions from geysers at its pole. south.
Until the 1980s, the structure of the rings was explained by means of the gravitational forces exerted by nearby satellites. The Voyager probes found, however, dark radial structures in the B ring called radial wedges (in English: spokes) that could not be explained in this way since their rotation around the rings was not consistent with orbital mechanics. These dark features are thought to interact with the planet's magnetic field, as their rotation around the rings followed the same speed as Saturn's magnetosphere. However the precise mechanism of its formation is still unknown. Wedges may come and go seasonally.
On August 17, 2005, instruments aboard the Cassini spacecraft revealed that something similar to an atmosphere exists around the ring system, made mostly of molecular oxygen. The data obtained have shown that the atmosphere in Saturn's ring system is very similar to that of the moons of Jupiter, Europa and Ganymede.
On September 19, 2006, NASA announced the discovery of a new ring on Saturn, by the Cassini spacecraft during a solar occultation, when the Sun passes directly behind Saturn and Cassini travels in the shadow left by Saturn. whereby the rings have bright lighting. Typically, a solar occultation can last an hour, but on September 17, 2006 it lasted 12 hours, the longest of the Cassini mission. Solar occultation gave Cassini the opportunity to map the presence of microscopic particles that are not normally visible in the ring system.
The barely discernible new ring is between the F Ring and the G Ring. This location coincides with the orbits of Saturn's moons Janus and Epimetheus, two co-orbital satellites of Saturn whose distances from Saturn's center differ less than the size of these satellites, so they describe a strange dance that leads them to exchange their orbits. The NASA researchers claimed that the impact of meteors on those moons has caused other particles to join the ring.
Cameras aboard the Cassini spacecraft captured images of icy material extending tens of thousands of kilometers from Enceladus, another confirmation that the moon is spewing material that could form the E ring. The satellite Enceladus could be seen through the E ring with its jets coming out of its surface resembling "fingers", directed at the ring in question. These jets are made up of very fine icy particles, which are ejected by geysers at Enceladus's South Pole and enter the E ring.
"Both the new ring and the unexpected structures in the E give us an important clue to how moons can launch small particles and sculpt their own local environments," said Matt Hedman, a research associate at Cornell University in Ithaca, New York.
The spacecraft also took a color photograph of Earth, about 1.5 billion kilometers away, in what appears to be a light blue sphere. In another image, taken on the same date, the Moon can also be seen.
Carolyn Porco, head of the team that operates the Cassini probe cameras at the Boulder Institute of Space Science in Colorado, said:
"Nothing has so much power to alter our perspective of ourselves and our place in the cosmos as those images of the Earth that we get from places as far as Saturn. »
NASA also announced on October 24, 2007 the discovery of a belt of micromoons on the outer edge of the A ring, ranging in size from a small truck to a stadium, probably caused by the destruction of a moon. small.
In October 2009, the Spitzer Space Telescope discovered a huge new ring around Saturn, much larger than those around it. After many centuries, it has gone unnoticed until now, because it is so rarefied that it is almost invisible. This new belt unfolds at the edge of the Saturnian system. Its mass begins about six million kilometers from the planet and extends to reach 13 million kilometers in diameter. One of Saturn's farthest satellites, Phoebe, orbits within the new ring, and is probably the source of its composition.
Magnetosphere
Saturn's magnetic field is much weaker than Jupiter's, and its magnetosphere is one-third that of Jupiter's. Saturn's magnetosphere consists of a set of toroidal radiation belts in which electrons and atomic nuclei are trapped. The belts extend about two million kilometers from the center of Saturn, and even more, away from the Sun, although the size of the magnetosphere varies depending on the strength of the solar wind (the flow of charged particles from the Sun).. The solar wind and Saturn's satellites and rings supply the particles that are trapped in the radiation belts. The 10 hour 39 minute 25 second rotation period of Saturn's interior was measured by Voyager 1 as it passed through the magnetosphere, which rotates synchronously with Saturn's interior. The magnetosphere interacts with the ionosphere, the upper layer of Saturn's atmosphere, causing auroral emissions of ultraviolet radiation; Recent studies show that instead of a ring of several smaller auroras, like Jupiter or Earth, there is a single large ring-shaped aurora at the north pole of the planet.
Circling the orbit of Titan, and extending to the orbit of Rhea, is a huge toroidal cloud of neutral hydrogen atoms. A disk of plasma, composed of hydrogen and possibly oxygen ions, extends from just outside the orbit of Tethys to almost that of Titan. The plasma rotates in near perfect synchronization with Saturn's magnetic field.
Saturn Space Exploration
Viewed from Earth, Saturn appears as a yellowish object, one of the brightest in the night sky. Viewed through a telescope, the A and B rings are easily seen, while the D and E rings are only visible. Come in optimal weather conditions. With highly sensitive telescopes located on Earth, pale belts and band structures parallel to the equator can be seen in the haze of Saturn's gaseous envelope.
Three US spacecraft greatly increased our understanding of the Saturn system: Pioneer 11 and Voyager 1 and 2, which flew by the planet in September 1979, November 1980, and August 1981, respectively. These spacecraft carried cameras and instruments to analyze radiation intensities and polarizations in the visible, ultraviolet, infrared, and radio regions of the electromagnetic spectrum. They were also equipped with instruments for the study of magnetic fields and for the detection of charged particles and interplanetary dust grains.
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In October 1997, the Cassini spacecraft was launched bound for Saturn, which also included the Huygens probe to explore Titan, the largest and most interesting of the planet's moons. This is NASA's latest big-budget project, in collaboration with the European Space Agency and the Italian Space Agency. After a nearly seven-year journey, Cassini was scheduled to collect data on Saturn and its satellites for another four years. In October 2002, the spacecraft obtained its first photograph of the planet, taken at a distance of 285 million kilometers, and in which Titan also appears. In June 2004, Cassini flew over Phoebe, another satellite of Saturn (the furthest away), obtaining spectacular images of its cratered surface. In July of the same year, the spacecraft entered Saturn's orbit. In January 2005, the Huygens probe passed through Titan's atmosphere and reached its surface, sending back to Earth data and images of great interest from the satellite.
- Important dates in the observation and exploration of Saturn
- 1610: Galileo observes through his telescope the rings of Saturn.
- 1655: Titan was discovered by Dutch astronomer Christiaan Huygens.
- 1659: Christiaan Huygens observes more clearly the rings of Saturn and describes its true appearance.
- 1789: the Mimas and Encelain moons are discovered by William Herschel.
- 1979: Overflight in Pioneer 11. On 1 September 1979, the American Pioneer 11 probe approached a distance of 20 000 km from the higher clouds.
- 1980: Accelerated by Jupiter's gravitational field, Voyager 1 probe reached Saturn on November 12 at a distance of 124 200 km. On this occasion he discovered complex structures in the ring system of the planet and obtained data from the atmosphere of Saturn and its largest satellite, Titan from which he passed to less than 6500 km.
- 1982: Voyager 2 approaches Saturn.
- 2004: Cassini/Huygens reaches Saturn. It became the first vehicle to orbit the distant world and approach its rings. The space mission has programmed its term during 2017.
- 2009: Thanks to the Spitzer space telescope, another ring is discovered around Saturn, which was invisible from our planet and which, in turn, is the largest in the solar system.
- 2017: In April 2017, Cassini/Huygens probe plunged and passed between Saturn and its closest ring at a rate of 124 000 km/h. Between Saturn and its nearest ring there is a distance of 2000 km, approximately. For this, he must have cut off the connection to Earth, returning it about 20 hours later. This was the first of 22 planned close encounters.
Observing Saturn
Saturn is an easy planet to observe, as it is visible in the sky most of the time and its rings can be seen with any telescope. Best seen when the planet is near or at opposition, that is, the position of a planet when it is at an elongation of 180°, thus appearing opposite the Sun in the sky. At opposition on January 13, 2005, Saturn could be seen with a maximum that will not be equaled until 2031, due to a quite favorable orientation of its rings with respect to Earth.
Saturn is visible to the naked eye in the night sky as a bright, yellowish luminous (non-blinking) point whose brightness normally varies between magnitude +1 and 0, it takes approximately 29 and a half years to complete one revolution in its orbit with respect to the background stars belonging to the zodiac. With optical support, such as with large binoculars or a telescope, a magnification of at least 20x is needed for most people to clearly distinguish Saturn's rings.
Saturn in various cultures
In Hindu astrology, there are nine planets, known as Navagrahas. Saturn is known as Sani or Shani, the Judge between all the planets, and determines each according to its own good or bad accomplished deeds.
Chinese and Japanese culture designate Saturn as the earth star within the traditional oriental scheme of using five elements to classify natural elements.
In Hebrew, Saturn is called Shabbathai. His Angel is Cassiel. His Intelligence, or beneficial spirit, is Agiel (layga), and his spirit (the darkest aspect) is Zazel (lzaz). See: Kabbalah.
In Turkish and Malay, his name is Zuhal, taken from the Arabic زحل.
Saturn was also known as Φαίνων by the Greeks.
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