How many moons does Saturn have?
Sen—Like the other large planets of our Solar System, such as Jupiter, Uranus and Neptune, Saturn has more than one moon—or 'natural satellite'. Many more, in fact. But how many moons does it have in total? Such a seemingly straightforward question has actually taken 359 years to answer.
It began in 1655 when the Dutch astronomer Christiaan Huygens used a small telescope to discover the first—and largest of Saturn's moons: Titan. At 5,152 kilometres in diameter Titan is 22.6 times smaller than Saturn and 40 per cent the size of Earth.
Between 1671 and 1684, four more moons were found. This time they were discovered by the Italian astronomer Giovanni Cassini and were named Tethys, Dione, Rhea and Iapetus.
It took over a century until two further moons were found by German-born British astronomer William Herschel: Mimas and Enceladus in 1789. Both Cassini and Herschel were able to find more moons by using increasingly improved telescopes than Huygens.
And so it was also for the discovery of Saturn's eighth moon, Hyperion—discovered in 1848 by English astronomer William Lassell. The development of photographic plates enabled the discovery of Phoebe—a tiny body only 436 kilometres in diameter—in 1899 by American astronomer William Pickering.
The small world Janus was the first of Saturn's moons to be discovered in the 20th century. Image credit: NASA / Jet Propulsion Laboratory / Space Science Institute.
And still the number of moons kept rising. The first 20th-century discovery was actually two for the price of one. In 1966 French astronomer Audouin Dollfus discovered Janus, when Saturn's rings were edge-on with respect to Earth. But studies of its orbit showed something was interacting with Janus. By 1978 it was confirmed by Stephen Larson, John Fountain and Richard Walker that there was indeed another moon sharing an orbit with Janus: Epimetheus.
Could the tally have stopped at 11? Not if NASA's Voyager probe had anything to do with it. Although the next three were observed from the ground, spacecraft would be essential in further moon discoveries. Helene, Telesto and Calypso are 'trojan moons' of Dione and Tethys—moons that can share an orbit with a larger body by sitting in a stable, gravitational region.
Both Voyager, and later the Cassini probes, have as of 2014, brought the total number of moons of Saturn to 62. Of those, 53 have official names whilst the other nine are still being studied. Such is the dynamism of Saturn's orbital environment that this number may change again in the future. So the most accurate answer to how many moons Saturn has is: 'many'.