Wandering Jupiter Helped Create Our Unusual Solar System

Like Miley Cyrus herself, millions of years ago a wandering Jupiter came in like a wrecking ball, destroying a first generation of inner planets and helping to create the unusual solar system we find ourselves in today.

That's at least according to a new study published in the journal Proceedings of the National Academy of Sciences, which aims to explain why our solar system is so different from others that astronomers have discovered in recent years.

"Now that we can look at our own solar system in the context of all these other planetary systems, one of the most interesting features is the absence of planets inside the orbit of Mercury," Gregory Laughlin, a study co-author, said in a statement. "The standard issue planetary system in our galaxy seems to be a set of super-Earths with alarmingly short orbital periods. Our solar system is looking increasingly like an oddball."

So how does Jupiter come into play? Well, researchers suggest a scenario known as the "Grand Track," - first put forth by another team of astronomers in 2011 - in which Jupiter journeyed toward the Sun until the formation of Saturn caused it to reverse course and settle in its current orbit. At that time, it's possible that rocky planets with deep atmospheres would have been forming close to the Sun from a dense disk of gas and dust, on their way to becoming typical "super-Earths" like astronomers have seen in other far-away solar systems.

However, based on numerical calculations, researchers determined that a juvenile Jupiter may have ruined this early version of our solar system, its gravitational pull sweeping the inner planets into close-knit, overlapping orbits that set them on a crash course to ultimately destroy one another in a series of collisions. (Scroll to read on...)

"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.

The resulting debris, he added, would then have been swallowed by the Sun due to a strong "headwind" from the dense gas still swirling around the star, pulling any newly-formed super-Earths with it.

Following this tumultuous beginning was a second generation of inner planets, formed from the minimal material left behind. If this Grand Track theory proves to be correct, it would explain why our solar system's inner planets are younger than the outer planets, as previous evidence suggests. In addition, the resulting inner planets - Mercury, Venus, Earth, and Mars - are also less massive and have much thinner atmospheres than would otherwise be expected.

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

In the search for life outside of Earth, planet hunters have detected thousands of exoplanets orbiting stars in our galaxy, including nearly 500 systems with multiple planets. And in some of these "typical" planetary systems are super-Earths - planets several times as massive as Earth, such as 55 Cancri e, for example. It's possible that Jupiter long ago wrecked any chances of our solar system boasting more than one habitable world.

"There is a lot of evidence that supports the idea of Jupiter's inward and then outward migration. Our work looks at the consequences of that. Jupiter's 'Grand Tack' may well have been a 'Grand Attack' on the original inner solar system," Laughlin concluded.

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