Scientists have spent a lot of time trying to simulate the birth of the solar system, partly to try and understand our solar system and partly to try and estimate how many other similar solar systems there are out there. But one thing that has confused them is Jupiter's moons - there aren't enough of them. According to all the simulations the moons of Jupiter should have made up about 10% of the total mass of Jupiter but they seem to only make up about 2%.
Robin Canup of the Southwest Research Institute, Colorado may have worked out where all those moons have gone. They have been eaten by Jupiter itself. Jupiter and its moons were formed out of a disk of gas and lumps of rock and ice orbiting itself. This then slowly collapsed under gravity as it lost energy to friction between the lumps of material. Moons which formed very early on in this process would have been surrounded by this disc which would have slowed them down causing them to fall lower and lower until they were swallowed up by Jupiter itself.
Jupiter could have swallowed up to 5 generations of moons, with those visible today being the last ones to form as the disk finally dissipated leaving them to continue orbiting for the intervening billions of years.