Introduction :

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine times that of Earth. It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive. Saturn is named after the Roman god of wealth and agriculture; its astronomical symbol (♄) represents the god's sickle. The Romans named the seventh day of the week Saturday, Sāturni diēs ("Saturn's Day") no later than the 2nd century for the planet Saturn.

Saturn's interior is most likely composed of a core of iron–nickel and rock (silicon and oxygen compounds). Its core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. An electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than the Earth's, but which has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph; 500 m/s), higher than on Jupiter but not as high as on Neptune. In January 2019, astronomers reported that a day on the planet Saturn has been determined to be 10h 33m 38s + 1m 52s
− 1m 19s , based on studies of the planet's C Ring.

The planet's most famous feature is its prominent ring system, which is composed mostly of ice particles, with a smaller amount of rocky debris and dust. At least 82 moons are known to orbit Saturn, of which 53 are officially named; this does not include the hundreds of moonlets in its rings. Titan, Saturn's largest moon and the second largest in the Solar System, is larger than the planet Mercury, although less massive, and is the only moon in the Solar System to have a substantial atmosphere.

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Physical characteristics :

Composite image comparing the sizes of Saturn and Earth

Saturn is a gas giant composed predominantly of hydrogen and helium. It lacks a definite surface, though it may have a solid core. Saturn's rotation causes it to have the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km. Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. The combination of the bulge and rotation rate means that the effective surface gravity along the equator, 8.96 m/s2, is 74% of what it is at the poles and is lower than the surface gravity of Earth. However, the equatorial escape velocity of nearly 36 km/s is much higher than that of Earth.

Saturn is the only planet of the Solar System that is less dense than water—about 30% less. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times Earth's mass, and Saturn is 95 times Earth's mass. Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.

Size and Distance :

With a radius of 36,183.7 miles (58,232 kilometers), Saturn is 9 times wider than Earth. If Earth were the size of a nickel, Saturn would be about as big as a volleyball.

From an average distance of 886 million miles (1.4 billion kilometers), Saturn is 9.5 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 80 minutes to travel from the Sun to Saturn.

Orbit and Rotation :

Saturn has the second-shortest day in the solar system. One day on Saturn takes only 10.7 hours (the time it takes for Saturn to rotate or spin around once), and Saturn makes a complete orbit around the Sun (a year in Saturnian time) in about 29.4 Earth years (10,756 Earth days).

Its axis is tilted by 26.73 degrees with respect to its orbit around the Sun, which is similar to Earth's 23.5-degree tilt. This means that, like Earth, Saturn experiences seasons.

Internal structure :

Diagram of Saturn, to scale

Despite consisting mostly of hydrogen and helium, most of Saturn's mass is not in the gas phase, because hydrogen becomes a non-ideal liquid when the density is above 0.01 g/cm3, which is reached at a radius containing 99.9% of Saturn's mass. The temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to be a metal in the deeper layers.

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium, with trace amounts of various volatiles. This core is similar in composition to Earth, but is more dense. The examination of Saturn's gravitational moment, in combination with physical models of the interior, has allowed constraints to be placed on the mass of Saturn's core. In 2004, scientists estimated that the core must be 9–22 times the mass of Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas.

Saturn has a hot interior, reaching 11,700 °C at its core, and radiates 2.5 times more energy into space than it receives from the Sun. Jupiter's thermal energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression, but such a process alone may not be sufficient to explain heat production for Saturn, because it is less massive. An alternative or additional mechanism may be generation of heat through the "raining out" of droplets of helium deep in Saturn's interior. As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves Saturn's outer layers depleted of helium. These descending droplets may have accumulated into a helium shell surrounding the core. Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter and ice giants Uranus and Neptune.

Atmosphere :

Methane bands circle Saturn. The moon Dione hangs below the rings to the right.

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The proportion of helium is significantly deficient compared to the abundance of this element in the Sun. The quantity of elements heavier than helium (metallicity) is not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these heavier elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.

Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and methane have been detected in Saturn's atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion. This photochemical cycle is modulated by Saturn's annual seasonal cycle.

Rings :

Saturn's rings are thought to be pieces of comets, asteroids or shattered moons that broke up before they reached the planet, torn apart by Saturn's powerful gravity. They are made of billions of small chunks of ice and rock coated with another material such as dust. The ring particles mostly range from tiny, dust-sized icy grains to chunks as big as a house. A few particles are as large as mountains. The rings would look mostly white if you looked at them from the cloud tops of Saturn, and interestingly, each ring orbits at a different speed around the planet.

Saturn's ring system extends up to 175,000 miles (282,000 kilometers) from the planet, yet the vertical height is typically about 30 feet (10 meters) in the main rings. Named alphabetically in the order they were discovered, the rings are relatively close to each other, with the exception of a gap measuring 2,920 miles (4,700 kilometers) wide called the Cassini Division that separates Rings A and B. The main rings are A, B and C. Rings D, E, F and G are fainter and more recently discovered.

Starting at Saturn and moving outward, there is the D ring, C ring, B ring, Cassini Division, A ring, F ring, G ring, and finally, the E ring. Much farther out, there is the very faint Phoebe ring in the orbit of Saturn's moon Phoebe.

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Rings of Saturn

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Saturn Atmosphere

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Saturn's Rotation

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Structure of Saturn

Facts about Saturn :

  • Saturn is the most distant planet that can be seen with the naked eye.
    It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope.

  • Saturn was known to the ancients, including the Babylonians and Far Eastern observers.
    It is named for the Roman god Saturnus, and was known to the Greeks as Cronus.

  • Saturn is the flattest planet.
    Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets.

  • Saturn orbits the Sun once every 29.4 Earth years.
    Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”.

  • Saturn’s upper atmosphere is divided into bands of clouds.
    The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures.

  • Saturn has oval-shaped storms similar to Jupiter’s.
    The region around its north pole has a hexagonal-shaped pattern of clouds. Scientists think this may be a wave pattern in the upper clouds. The planet also has a vortex over its south pole that resembles a hurricane-like storm.

  • Saturn is made mostly of hydrogen.
    It exists in layers that get denser farther into the planet. Eventually, deep inside, the hydrogen becomes metallic. At the core lies a hot interior.

  • Saturn has the most extensive rings in the solar system.

  • The Saturnian rings are made mostly of chunks of ice and small amounts of carbonaceous dust. The rings stretch out more than 120,700 km from the planet, but are amazingly thin: only about 20 meters thick.

  • Saturn has 150 moons and smaller moonlets.
    All are frozen worlds. The largest moons are Titan and Rhea. Enceladus appears to have an ocean below its frozen surface.

  • Titan is a moon with complex and dense nitrogen-rich atmosphere.
    It is composed mostly of water ice and rock. Its frozen surface has lakes of liquid methane and landscapes covered with frozen nitrogen. Planetary scientists consider Titan to be a possible harbour for life, but not Earth-like life.

  • Four spacecraft have visited Saturn.
    Pioneer 11, Voyager 1 and 2, and the Cassini-Huygens mission have all studied the planet. Cassini orbited Saturn from July 2004 until September 2017, sending back a wealth of data about the planet, its moons, and rings.

  • Saturn has more moons than any other planet.
    20 new moons were discovered in 2019 bring the total to 82, 3 more than Jupiter.

3 D Model of Saturn

Source: NASA Visualization Technology Applications and Development (VTAD)

Source Credits : NASA, Wikipedia and Space Facts.