The constant heavens?

Okay, here's one to make you think a minute, at least, if such things interest you.

visiting the family roost is always a great chance to catch up on recent astronomical theory, since the pater familias is in the business and all. Here's something very interesting that I hadn't heard before.

As you may well know, the theory goes that the solar system and the sun formed from a nebulous cloud of gases and particulate matter which gradually condensed. The sun, by far the largest object in the solar system, eventually gained sufficient mass that atomic fusion began within it. The early solar wind after the sun's ignition tended to push gases not absorbed into the sun out into the outer solar system, where the gas giant planets formed, while leaving the heavier materials near the center of the solar system to form the rocky, inner planets. As the planets were solidifying, a heavy bombardment of rock and ice debris produced heavy cratering and periodically melted some or all of their crusts until most of the cross orbital objects had been absorbed. During this period, the earth was struck by an object around the size of mars, which blew off huge portions of the earth's lighter outer crust into space. Much of this debris did not escape the earth's gravity well and accreted to form the moon. The moon itself remains heavily scarred from the latter stages of the heavy bombardment.

All of this has been accepted theory for several decades, but over the last decade or so, an additional refinement has been added due to evidence of a resurgence of heavy cratering activity (as measured from the more-or-less undisturbed crater record on the moon) about 700 million years after the end of the heavy bombardment. Based on this apparent spike in cratering activity, and studying the orbital dynamics of Uranus, Neptune and Pluto, many astronomers apparently now believe that Neptune and Pluto were both originally somewhat closer to the sun, and that Uranus may in fact have originally have been the farthest out of the nine planets.

About 700 million years after the end of the heavy bombardment, they believe that gravitational interactions between the outer planets pushed Neptune and Pluto out into more distant orbits, and farther out of the plane of the ecliptic.

This movement in the outer solar system in turn disturbed the orbits of a number of comets and asteroids, some of which were thrown out of the solar system entirely while others were thrown inwards, causing a brief but sharp spike in cratering on the inner planets.

Although these sound like pretty crazy events, even larger shake-ups may be common in the universe. A number of the planets that have been discovered circling other stars in the last decade have been gas giants as large as or larger than Jupiter, yet orbiting very close to their stars. From what we currently understand, a gas giant cannot form that close to its star, so it seems likely that these close orbiting gas giants formed much farther out and were then pushed or pulled inwards by some sort of gravitational interaction with other objects.

Or, of course, they could represent evidence of intelligent falling.