The theory is that Jupiter travelled in towards the Sun before moving outwards again, and in the process smashed the first-generation into the Sun, making way for Earth.
The scenario has been proposed by Konstantin Batygin, a Caltech planetary scientist, and Gregory Laughlin of UC Santa Cruz in the online edition of the Proceedings of the National Academy of Sciences (PNAS).
“Our work suggests that Jupiter’s inward-outward migration could have destroyed a first generation of planets and set the stage for the formation of the mass-depleted terrestrial planets that our solar system has today,” says Batygin, an assistant professor of planetary science.
The theory could explain why our solar system is so different from those in our galactic neighbourhood. Typically they have one or more planets that are substantially more massive than Earth orbiting closer to their suns than Mercury does, but very few objects at distances beyond.
“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,” says Batygin. “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 proposed model of our solar system model builds on the Grand Tack scenario, which was first posed in 2001 by a group at Queen Mary University of London. In that scenario, during the first few million years of the solar system’s life, when planetary bodies were still embedded in a disc of gas and dust around a relatively young Sun, Jupiter became so massive and gravitationally influential that it was able to clear a gap in the disc, with the Sun then pulling Jupiter inward.
Only Saturn stopped it from being destroyed on the face of the Sun.
Batygin suggests Saturn formed after Jupiter but was pulled toward the Sun at a faster rate, allowing it to catch up and the two bodies to exert a gravitational influence on one another, reversing the planets’ migration direction and sending them back outward in the solar system.
Batygin speculates that the inner solar system was cleared as Jupiter pulled all objects along until they smashed into each other and spiralled into the sun.
