Our Solar System May Have Been Home to Super-Earths

Posted on March 23, 2015

Snapshot from simulation of Jupiter's grand inward migration

A number of super-Earths may once have been part of our inner solar system. This would have been long before Mercury, Venus, Mars and Earth formed. The scenario has been suggested by Konstantin Batygin, a Caltech planetary scientist, and Gregory Laughlin of UC Santa Cruz. Their calculations and simulations suggest this was a possibility. The image above is a snapshot from one of the simulations with Jupiter's orbit represented by the thick white circle.

The super-Earths are long gone now. The scientists say they would have broken up and fallen into the sun billions of years ago during a great inward journey made by Jupiter. It could explain why our solar system seems to differ from the exoplanet solar systems of other stars. Most of these systems have one or more super-Earths orbiting closer to their suns than Mercury does.

Batygin says in a statement, "Indeed, it appears that the solar system today is not the common representative of the galactic planetary census. Instead we are something of an outlier. But there is no reason to think that the dominant mode of planet formation throughout the galaxy should not have occurred here. It is more likely that subsequent changes have altered its original makeup."

The astronomers say Jupiter and the Grand Tack scenario is crucial to understanding how the solar system came to be the way it is today. Under the Grand Tack scenario Jupiter became so massive that it cleared a gap in the sun's disk. As the sun pulled the disk's gas in toward itself Jupiter also began drifting inward. As Jupiter moved inward it picked up primitive planetary building blocks and drove them into eccentric orbits that overlapped the unperturbed part of the planetary disk. This set off a cascade of collisions that would have sent any interior planets (the super-Earths) into the sun. A second part of the Grand Tack scenario involves Jupiter migrating back away from the sun again. This is thought to have took place due to an orbital resonance with Saturn.

The researchers say Jupiter's inward and then outward migration helps explain the low overall mass of the Solar System's terrestrial planets, as well as the absence of planets with a < 0.4 AU. The planets Mercury, Venus, Earth, and Mars may have formed from planetesimals that clumped together after Jupiter's Grand Tack.

The researchers explain their findings in a paper called, "Jupiter's decisive role in the inner Solar System's early evolution," which was published in PNAS.

Image: K. Batygin/Caltech