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Jupiter May Have Destroyed Early Planets And Paved The Way For Earth

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NASA's Kepler spacecraft has, to date, enabled astronomers to discover over 1,000 planets outside of our solar system. But there's a funny thing about the solar systems astronomers discovered - they don't look much like ours at all. Most of them have larger, "super-Earths" - planets smaller than Neptune but bigger than Earth - located very close to the Sun.

Our solar system, by contrast, doesn't. Why?

Research conducted by astronomer Gregory Laughlin and astronomer/Forbes 30 Under 30 list member Konstantin Batygin suggest that the responsibility may lie with the planets Jupiter and Saturn.

In a paper published this week in the Proceedings of the National Academy of Sciences, the two astronomers suggest that in the early life of the solar system, Jupiter traveled much closer to the Sun than it is now - close to 140 million miles away - before reversing course and finding itself in its present orbit about 483 million miles from the Sun thanks to its gravitational interaction between the two gas giants.

Given Jupiter's massive size, its strong gravity may have taken its toll on any super-Earths that existed in the early years of the Solar System by literally shifting their orbits so that they fell into the Sun.

"In this scenario, the Solar System’s terrestrial planets formed from gas-starved mass-depleted debris that remained," the authors wrote in the paper.

"All of this fits beautifully with other recent developments in understanding how the solar system evolved, while filling in some gaps," Batygin said in a statement.

The idea that Jupiter and Saturn once traveled closer to the Sun isn't original to this paper. Called the "Grand Tack scenario," it was developed in part by a research group in 2001 and later revived again in 2011 to explain some of what astronomers were learning about the early Solar System. (Astronomer Kevin Walsh has a great page of resources about this theory that you can explore here.)

For this research, Laughlin & Batygin ran computer simultations involving the Grand Tack scenario to see how it would impact the Solar System if, like most Solar Systems outside of ours, "super-Earths" had formed near the Sun.

"It's the same thing we worry about if satellites were to be destroyed in low-Earth orbit. Their fragments would start smashing into other satellites and you'd risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system," Laughlin explained in a press release.

With the matter and gasses of the super-Earths being driven to the Sun, there was a lot less material available to produce planets. The result, then, were the small, rocky inner planets of our Solar System - including Earth.

If this theory pans out, Earth-like planets may be hard to find in the wider universe .

The key reason why is Saturn. In most solar systems, only one large gas giant like Jupiter will for in its early years. So when it gets closer to its Sun, it stops and finds an orbit that's similar to that of Earth's. And the super-Earths also typically remain intact.

But in our solar system, both Jupiter and Saturn formed relatively early. And as both planets moved towards the Sun, the complex gravitational actions between them and the clouds of hot gas and matter that still existed caused two rare events. First, it led to the two planets moving back away from the Sun and into their current orbits. Second, it led to the collisions that gravitational disturbances that destroyed our system's super-Earth's.

Since solar systems rarely produce two large gas giants like Jupiter and Saturn, it's likely that planets like ours are relatively unique.

"One of the predictions of our theory is that truly Earth-like planets, with solid surfaces and modest atmospheric pressures, are rare," Laughlin noted.

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