Since ancient times the planet Saturn was among seven celestial bodies, along with Mercury, Venus, Mars, Jupiter, the Moon and the Sun, that were visible in the night sky. Saturn is the second largest planet in our Solar System and because of its rings, it is considered to be one of the most beautiful objects in the Universe. Until the Voyager 1 space mission in the late 70s of the last century, Saturn was the only known planet that could boast a series of rings. The planet Saturn is ranked among the four giant planets, similar to Jupiter (its weight is only one third). It is a largely gaseous body, composed primarily of hydrogen with the lowest density in the Solar System. An obvious Saturn’s flattening at the poles is caused by rapid rotation. The inclination of the axis of rotation relative to the orbit is of great importance in terms of visibility of Saturn’s rings.

Galileo Galilei was the first

Saturn was the most distant of the five planets known to the ancients. An italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope in 1610. To his surprise, he saw a pair of objects one on either side of the planet. He sketched them as separate spheres and wrote that Saturn appeared to be triple-bodied. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo’s, proposed that Saturn was surrounded by a thin, flat ring.

Last space mission to the ring planet is called after Italian astronomer

A composite of 21 photos of Saturn and its beautiful rings, captured by NASA's Cassini spacecraft on Oct. 28, 2016. Credit: Ian Regan/Space Science Institute/JPL-Caltech/NASA

Italian-born astronomer Jean-Dominique Cassini discovered a "division" between what are now called the A and B rings in 1675. It is now known that the gravitational influence of Saturn’s moon Mimas is responsible for the Cassini Division, which is 4,800 kilometers wide. Giant planet Saturn is composed mostly of hydrogen and helium. Winds in its atmosphere reach speed almost 500 m/s in the equatorial area. Superfast winds in combination with planet’s interior heat might cause the gold and yellow bands in the Saturn’s atmosphere.

Saturn's ring system

NASA's Cassini spacecraft captured this view of Saturn's "Death Star" moon Mimas on Nov. 19, 2016, from a distance of about 53,000 miles (85,000 kilometers). Credit: NASA/JPL-Caltech/Space Science Institute

This giant planet has the most extensive and complex ring system of all planets in our Solar System, which are spread up to hundreds of thousands of km from the planet. The first space probe to visit Saturn was Pioneer 11, in September 1979. The research space mission was traveling under the ring system and has sent back to our planet many useful pictures of the planetary rings. However, the images showed little new information about Saturn’s clouds and atmosphere. NASA’s two Voyager 1 and 2 spacecraft mission flew by and photographed Saturn in the early 1980s. They revealed that Saturn’s rings are made mostly out of water ice. The Voyager space probes provided many pictures and data about Saturn. They found three new moons around the planet, four additional faint rings and provided pictures of atmospheric circulation. Before the Voyager space missions, information about Saturn’s atmosphere was limited because astronomers could see only the tops of the clouds from Earth.

Hubble Space Telescope images show aurorae

Saturn's moon Tethys with its prominent Odysseus Crater silently slips behind Saturn's largest moon Titan. Credit: NASA/JPL/Space Science Institute

Planet Saturn has 53 known natural satellites or moons, and there are probably many more waiting to be discovered. Saturn’s largest satellite, Titan, is the second-largest moon in the Solar System, a bit bigger than the planet Mercury. Planet Saturn, its planetary rings and many of the satellites lie totally within Saturn’s enormous magnetosphere. It is an area where the behavior of electrically charged particles is influenced more by Saturn’s magnetic field than by the energy of solar wind. The Hubble Space Telescope, while orbiting Earth, captured the first images of aurora in Saturn’s atmosphere in 1994. It has also captured images of topographical features on Saturn’s largest moon, the Titan. Hubble Space Telescope images show that Saturn’s polar regions have aurorae similar to Earth’s. Aurorae occur when charged particles spiral into a planet’s atmosphere along magnetic field lines.

Cassini space mission to planet Saturn

Cassini delivers this stunning vista showing small, battered Epimetheus and smog-enshrouded Titan, with Saturn's A and F rings stretching across the scene. Credit: NASA/JPL/Space Science Institute

The latest chapter of getting to know Saturn took place between 2004 and 2017, as the Cassini spacecraft continued its exploration of the Saturn planetary system. The Cassini mission to Saturn (named after astronomer Giovanni Cassini) was one of the most ambitious ever attempted. It was the joint venture of NASA, the European Space Agency (ESA) and the Italian Space Agency and it was designed to explore the whole Saturnian system, the planet itself, its atmosphere, planetary rings, magnetosphere and some of its moons. The orbiter, the largest interplanetary spacecraft ever constructed by NASA, has been launched from Cape Canaveral Air Force Station in Florida in October 1997, with the European Space Agency’s Huygens probe aboard. Seven year cruise to Saturn on a gravity-assist trajectory: two swingbys of Venus, one of Earth and one of Jupiter to give the spacecraft the boost needed to reach Saturn. The Cassini space probe reached Saturn in 2004 and went into orbit around the planet. Cassini plunged between Saturn’s two outer rings before it slowed down enough to be captured by Saturn’s gravity and begin its four-year orbit of the planet.

Cassini released small probe called Huygens

Instruments on board space probe Cassini have also taken some pictures of the planet Saturn largest moon. It has been found that Titan is surrounded by a thick atmosphere with areas of water ice on its surface. The Huygens probe descended through Titan’s atmosphere in January 2005, collecting data on the moon’s surface and atmosphere. Space probe landed via parachute on Titan’s surface in the mud like wet clay covered by a thin crust. The ground temperature was a chilling -180°C. Huygens’s was the first successful attempt by humans trying to land a probe on a space body in the outer Solar System.

It drew closer to Saturn than ever in late 2016, showing an up-close view of the planet for the first time. The Cassini space probe discovered eight new moons of Saturn from 2004 to 2009. The primary mission of Cassini space probe ended in 2008. The probe’s mission was extended to September 2010 and then extended again to 2017, to study a full period of Saturn’s seasons. At the end of its final orbit around the planet, as Cassini fell into Saturn’s atmosphere, it completes its 20-year space mission. By this intentional fall, it has been ensured that the biologically interesting moons - the Enceladus and the Titan, would not be contaminated by microbes that might have survived the journey from Earth.