As astronomers have discovered more and more alien worlds orbiting stars far, far away, they’ve noticed something. Our own system is a little odd.
Most planetary systems have a few super-Earths—rocky planets a few times larger than ours—orbiting close and hot to their star. They also tend to be swathed in thick layers of vapor, meaning they "tend to have very thick and massive atmospheres with pressures that exceed that of the Earth by factors of hundreds, if not thousands," Konstantin Batygin, a planetary scientist at the California Institute of Technology in Pasadena, told Space.com. And in our odd system, "the atmospheres of our terrestrial planets are exceptionally thin." And even when systems do include gas giants, those planets tend to be massive, hot ones, also orbiting close to their stars.
Thank Jupiter for our system's weirdness. If the gas giant hadn’t come in like a giant wrecking ball and smashed up all the early planets forming in the inner solar system, we too would be like everyone else.
Batygin and his colleague Greg Laughlin recently modeled a version of the early solar system where Jupiter formed first and wandered in close to the sun. Only the birth of Saturn pulled Jupiter out to its current orbit. That wandering, in the model, had an effect: it threw the rocky worlds in the early solar system crashing in to each other.
The resulting debris would then have spiraled into the sun under the influence of a strong "headwind" from the dense gas still swirling around the sun. The ingoing avalanche would have destroyed any newly-formed super-Earths by driving them into the sun. A second generation of inner planets would have formed later from the depleted material that was left behind, consistent with evidence that our solar system's inner planets are younger than the outer planets. The resulting inner planets— Mercury, Venus, Earth, and Mars — are also less massive and have much thinner atmospheres than would otherwise be expected, Laughlin said.
The researchers published their findings in Proceedings of the National Academy of Sciences.
And if that was the way that the solar system formed—gas giant planet pulverizing and all—it's what gave life on Earth a chance to get started.