> as did the Earth when the earth year had only 10 months of 30 days. Wonder what might have bumped into it?
Nothing. What has happened is that the sun has lost considerable mass over the last 5 billion years, whereas the planets have not lost much in the way of kinetic energy or angular momentum WRT their orbits. So as the sun lost mass, the planets sloooowly drifted out. A process which will continue.
Bodies in prograde orbits enjoy a transfer of momentum from the rotation parent body, and migrate outward. However, that is a slow process. It hasn't anything to do with any loss of mass of the Sun. Also, the atmosphere of Jupiter is enriched in noble gases, and members of the team which discovered that suggested that it indicated an origin for Jupiter that lay past the outer planets today.