The planets in our solar system may actually be a second generation of orbiting worlds, with the first set of different worlds having been destroyed.
The culprit? Blame a cosmic bully, astronomers say — Jupiter.
The gas giant may have invaded the early inner solar system like a wrecking ball, sweeping away an entire collection of early planets before orbiting back out to its current state, they say.
The results of a study published in the Proceedings of the National Academy of Sciences could explain why our solar system is so differently constituted compared with the hundreds of other planetary systems astronomers have been discovering orbiting distant stars.
"Indeed, it appears that the solar system today is not the common representative of the galactic planetary census," says planetary scientist Konstantin Batygin at the California Institute of Technology. "Instead we are something of an outlier."
If hundreds of other planetary systems are to be considered normal, then our solar system should have some more planets even closer to the sun than Mercury.
The typical planetary system astronomers have discovered displays a few super-Earths — rock-like worlds about 10 times the size of Earth's mass — orbiting much closer to their stars than Mercury does our sun.
Even in other solar systems that possess gas giants like Jupiter and Saturn, those worlds orbit much closer to the sun than we see in our cosmic home, the researchers point out.
"Our solar system is looking increasingly like an oddball," says study co-author Gregory Laughlin, an astronomer at the University of California, Santa Cruz.
That could be down to something proposed by some researchers, dubbed the Grand Tack theory, that suggests Jupiter got pulled toward the sun after its formation, was caught up in the pull of interplanetary dust and went rampaging through the inner solar system.
That only ended when it caught Saturn in its own gravitational pull, and the two gas giants hauled each other back out to their current positions, the theory suggests.
During its "wrecking ball" swing through the inner solar system, Jupiter could have disrupted the orbits of any not quite fully formed protoplanets, causing a chain reaction of destructive collisions.
The resulting onslaught of debris could have destroyed any planets unlucky enough to be caught in Jupiter's wake, the researchers suggest.
"It's the same thing we worry about if satellites were to be destroyed in low-Earth orbit," says Laughlin, explaining how debris could start crashing into other satellites with the risk of a chain reaction of impacts. "Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system."
