What's better than a cannibal planet? How about a GIANT cannibal planet? How about a GIANT cannibal planet that's in our solar system with us? No, it's not Unicron - it's Jupiter, the gas monster that now seems to have much more violence in its history than a mere storm system larger than the Earth.
When the sun first formed out of interstellar gas, the whole assembly had a fairly high rotational speed, so not all the dust fell into the fusion reactor furnace. A lot of it got spun out into a rotating disk. Local density fluctuations in this disk formed the cores of planets and moons, which gobbled up unused material to grow. Gas-cored planets like Jupiter and Saturn formed first, far more quickly than their rocky siblings.
The problem for Jupiter's doomed moons was that maintaining an orbit around a larger body means balancing centripetal acceleration against gravitational attraction, but these early orbiters had to slog through a relatively thick dust medium. The constant friction slowed the satellites until they eventually fell into the planet. This happened five times, in fact, until the current generation of moons formed just as the disk was running out of material.
Even more awesomely, the same picture applies on the larger scale - early gas-cored planets which happened to form too close to the sun could also have been dragged to extinction by dust friction. But since all the evidence was literally tossed into a giant fusion reactor, we may never know.
Posted by Luke McKinney.