Saturn has overtaken Jupiter as the planet with the most moons, according to US researchers. A team discovered a haul of 20 new moons orbiting the ringed planet, bringing its total to 82; Jupiter, by contrast, has 79 natural satellites. The moons were discovered using the Subaru telescope on Maunakea, Hawaii. The gas giants Jupiter and Saturn, in fact account for over two-thirds of all the natural satellites found in the solar system. Even though both Jupiter and Saturn have 53 confirmed moons each, Satum pips ahead of Jupiter when the provisional moons are also counted. With 29 provisional moons as opposed to Jupiters 26, Saturn has a total of 82 discovered moons for now, while Jupiter has 79.
Titan, Saturn’s largest moon, was the first satellite of the planet to be discovered when it was observed by Dutch mathematician and astronomer Christiaan Huygens in 1655. Italian mathematician and astronomer Giovanni Domenico Cassini discovered the next four moons of Saturn between 1671 and 1684.
Cassini’s “stars”
Following his discovery of lapetus in 1671 and Rhea in 1672, Cassini discovered Tethys and Dione on March 21, 1684 using his refractor telescope. Cassini, however, collectively named the four moons that he discovered as Sidera Lodoicea – Latin for Stars of Louis – after the French King Louis XIV.
For a period, Saturn’s moons were called by numbers based on their distance from the planet. It was English astronomer John Herschel who suggested that the moons of Saturn be related with the Greek mythical brothers and sisters of Kronus – the equivalent of the Roman god Saturn. That’s how Tethys and Dione have ended up with the names we now know.
For a period, Saturn’s moons were called by numbers based on their distance from the planet. It was English astronomer John Herschel who suggested that the moons of Saturn be related with the Greek mythical brothers and sisters of Kronus – the equivalent of the Roman god Saturn. That’s how Tethys and Dione have ended up with the names we now know.
Trojan moons
Tethys and Dione are unique in the fact that they have trojan moons. When larger moons have moons of their own, those moons are called trojans.
Both Tethys and Dione have gravitationally locked two smaller moons into their respective sub systems. The two smaller moons in each of these systems are held in Lagrangian points-points based on calculations of the French astronomer Joseph-Louis Lagrange and where objects are stable with the larger controlling body – and complete their orbit around Saturn as a unit.
While Telesto and Calypso are the two trojans of Tethys, Helene and Polydeuces are Dione’s two moons. The existence of these trojans implies that the Lagrangian points of Tethys and Dione have been stable for millions of years despite facing outside influences.
Locked in phase Just like Earth’s moon, both Tethys and Dione are tidally locked in phase with their parent planet. This means that the same side of Tethys and Dione always face towards Saturn.
With a mean radius of 533 km, Tethys is Saturn’s fifth largest moon and takes about 45 hours to orbit the planet. Cold, airless, and heavily scarred, Tethys has a density that is 0.97 times that of liquid water. This suggests that Tethys is likely composed almost entirely of water ice, along with a small amount of rock.
Dione, meanwhile, has a mean radius of 562 km and orbits Saturn once in 2.7 days at a distance of 3,77,400 km – approximately the same distance that our moon orbits around the Earth. As Dione’s density is 1.48 times that of liquid water, probably one-third of it is made up of a dense core like silicate rock and the remaining is maybe made up of ice.
While Tethys and Dione were just tiny dots to astronomers for years after their discovery, images taken by Voyager (1 and 2) in the 1980s threw more light on these far away moons. The Cassini-Huygens mission has since then provided much more detail, but there’s still plenty to learn about these two moons.
Picture Credit : Google
