I like watching NUMB3RS. Two brothers, one a top-notch FBI agent, the other a star mathematician, seek to solve tricky cases using sparse, difficult-to-gather data. Often, catching the criminal depends on extracting useful information from distorted or fragmentary clues. As you might expect, the mathematical skills of one brother play a key role in obtaining that info. Similarly, scientists sometimes use clues to reconstruct long-past events in the solar system’s history. In particular, researchers have studied the distribution of objects in the asteroid belt to see how the orbits of the gas giant planets changed during the solar system’s early history.
Jupiter’s large gravitational tug on the asteroid belt objects clears out gaps in the belt. First observed and explained by Daniel Kirkwood in 1857, these gaps were once occupied by asteroids with orbital periods a simple fraction of Jupiter’s. Any asteroid in this region experienced repeated gravitational tugs that eventually ejected it from the belt.
The main gaps match well with predictions based on the current orbits of Jupiter and Saturn. However, as astronomers look at the regions outside the Kirkwood gaps, they find evidence of ancient migrations by Jupiter and Saturn. In particular, asteroids in the “non-gap” regions should be stable over the history of the solar system, yet these regions show evidence of asteroid depletion.
A pair of planetary scientists from the University of Arizona recently discovered an explanation for the asteroid depletion. Jupiter and Saturn formed in orbits different than the ones in which they currently reside. Interactions with the planetesimals left over from planet formation caused their orbits to change. The team found they could explain the asteroid distribution if Jupiter formed farther out and drifted toward the Sun and the other three gas giants formed closer and migrated farther from the Sun. This migration would have occurred roughly four billion years ago and likely caused the Late Heavy Bombardment (LHB) events on Earth.
Mercury and the Moon still show the impact craters resulting from the LHB. Importantly, the LHB removed a large fraction of the remaining comets and asteroids from the inner solar system. Consequently, Earth has experienced significantly fewer devastating impacts since life’s introduction to the planet than it would have if the LHB hadn’t occurred.
The migration of the gas giants demonstrates the dynamic behavior of the early solar system and how it prepared Earth for the abundance and diversity of life to come. These results add one more piece of evidence to a growing case for a supernatural Creator who fashioned Earth for human beings.