Fifty years ago, astronomers knew of 12 moons orbiting Jupiter and 11 circling Saturn. That made sense to astronomers. Jupiter is the largest planet in our solar system and had the strongest gravitational pull of any of the planets, so it seemed logical that it would have more moons. Jupiter orbits the sun at the outer edge of the asteroid belt, so it has many opportunities to steal some as moons. Most astronomers assumed that we would eventually find even more Jovian moons as telescopes and digital cameras improved and as we developed spacecraft to explore the planes in detail.
Over the years, these new techniques did allow astronomers to find more moons of both planets. Over the years, the two planets flip-flopped back and forth as to which possessed the most moons.
Jupiter possesses four moons that are among the largest in our solar system. They were first seen by Galileo in 1610. He was the first person known to have pointed a telescope into the night sky. Those four moons are Io, Europa, Ganymede, and Callisto. All four are visible in any amateur telescope or even a good pair of binoculars. Ganymede is the largest moon in our solar system. Jupiter’s other three Galilean moons are all among the 6 largest moons of our solar system.
In 1655, astronomer Christiaan Huygens discovered Titan orbiting Saturn. Titan is the second largest moon of our solar system, and the only moon with a thick atmosphere, half again thicker than our own atmosphere.
With the development of larger and larger ground-based telescopes and more advanced cameras, both planets were found to have many more moons. As the space age opened, craft like Voyager 1 and 2, Juno, which orbited Jupiter, and Cassini, which orbited Saturn, we discovered even more around each planet.
As of February of this year, astronomers added 12 more moons to Jupiter. Jupiter was known to have 95 moons. Saturn trailed with 83 moons. Those numbers are a far cry from what we knew in 1973. Jupiter was again the king of moons, as most astronomers expected it would be. Jupiter’s lead wouldn’t last long.
Last month, astronomers announced the discovery of 62 previously unknown moons around Saturn, bringing its current total to 145. The recent discoveries around both giant planets are quite small, as moons go, or else we’d have discovered them some time ago.
That’s a lot of moons, far more than any astronomer would have guessed 50 years ago. But I doubt we are done discovering moons around either planet. And it’s likely the two ice giant planets, Uranus, currently known to have 27 moons, and Neptune, with 14 moons, will eventually be discovered to have many more moons, too.
Each month, I write an astronomy-related column piece for
the Oklahoman newspaper. After it is published there, I post that same column to my blog page.
