However, the true history of the solar system is more riotous. Giant planets migrated in and out, tossing interplanetary flotsam and jetsam far and wide. New clues to this tumultuous past come from the asteroid belt.
“We found that the giant planets shook up the asteroids like flakes in a snow globe,” said Francesca DeMeo from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Millions of asteroids circle the Sun between the orbits of Mars and Jupiter in a region known as the main asteroid belt. Traditionally, they were viewed as the pieces of a failed planet that was prevented from forming by the influence of Jupiter’s powerful gravity. Their compositions seemed to vary methodically from drier to wetter, due to the drop in temperature as you move away from the Sun.
That traditional view changed as astronomers recognized that the current residents of the main asteroid belt weren’t all there from the start. In the early history of our solar system, the giant planets ran amok, migrating inward and outward substantially. Jupiter may have moved as close to the Sun as Mars is now. In the process, it swept the asteroid belt nearly clean, leaving only a 0.10 percent of its original population.
As the planets migrated, they stirred the contents of the solar system. Objects from as close to the Sun as Mercury and as far out as Neptune all collected in the main asteroid belt.
“The asteroid belt is a melting pot of objects arriving from diverse locations and backgrounds,” said DeMeo.
Using data from the Sloan Digital Sky Survey, DeMeo and Benoit Carry from the Paris Observatory examined the compositions of thousands of asteroids within the main belt. They found that the asteroid belt is more diverse than previously realized, especially when you look at the smaller asteroids.
This finding has interesting implications for the history of Earth. Astronomers have theorized that long-ago asteroid impacts delivered much of the water now filling Earth’s oceans. If true, the stirring provided by migrating planets may have been essential to bringing those asteroids.
This raises the question of whether an Earth-like exoplanet would also require a rain of asteroids to bring water and make it habitable. If so, then Earth-like worlds might be rarer than we thought.