New Planet Formation Theory

A new theory of how the Solar System developed suggests the traditional theory is unworkable.

That traditional theory holds that the planets formed by coalescing out of material in a disk of gas and dust that surrounded the early Sun-- and that they did so in roughly their present orbits. The new theory says that there would never have been enough concentrated mass at the distances of Uranus and Neptune to allow those planets to form within the planetary formation window of a few hundred million years.

Instead, the new theory postulates a denser, more massive initial disk and argues that all the planets formed at about half their current distances, and migrated out to their current orbits, perhaps under the influence of a passing comet. Perhaps, too, a close brush with a passing star stretched the Sun's family of planets out to their current positions. Interestingly, the new theory also argues that Neptune and Uranus switched positions as they made their way to their present orbits.