How Jupiter May Have Destroyed the Inner Solar System

In the early days of our solar system, a rogue Jupiter destroyed everything in its path.

And according to the researchers, the Earth owes its very existence to these collisions.

Caltech astrophysicist Konstantin Batygin and UCSC’s Greg Laughlin have conducted statistical studies based on Jupiter’s wandering orbit, hoping to focus on what makes our solar system so seemingly unique. Their findings were published today in the Proceedings of the National Academy of Sciences.

Exoplanetary research, such as NASA’s Kepler mission, suggests a “default” mode of planetary formation. In this model, systems that develop around stars similar to the Sun tend to produce at least one massive planet in close orbit.

“The innermost realm of our own solar system, on the other hand, is completely, mysteriously empty,” Dr. Laughlin said. “So it is the context provided by the extrasolar planets that has given us a clue that something is unusual with us.”

Until fairly recently, there was no explanation as to how these planets could have disappeared. In 2012, researchers described for the first time an interplanetary model based on the suggestion that Jupiter’s orbit is not fixed – that it migrated closer to the sun during the formation of our solar system, only to turn around and move away over millions of years. Because it looked like a sailboat “tacking” around a buoy, the researchers dubbed it “the Grand Tack hypothesis”.

As Jupiter retreated into a close orbit, gravitational disturbances would have precipitated the inner planets into each other. Then, “headwinds” of swirling gas would have propelled the remaining debris into the Sun. Jupiter would have remained, for the moment, in close orbit with its central star.

Typically, this is where the story ends. The formation of giant planets is unusual, so two would be considered a rarity. But Jupiter was drawn to another massive celestial body – Saturn. As the space between Jupiter and the Sun widened, new planets were able to develop from the material left over from the collisions. This theory is supported by evidence that our inner to medium planets – Mercury, Venus, Earth, and Mars – are younger than our outer planets. They are also rocky, rather than gaseous, and their atmospheres are relatively thin.

“Over the years, we’ve looked at a number of approaches to cleaning up the inner solar system,” Laughlin said, “and none of them showed particularly promise. But then Konstantin pointed out the idea of ‘a cascade of collisions, and it became, as far as we could tell, very straightforward to figure out what could have happened. It was surprising that the Grand Tack, which received a lot of attention at the in recent years, explains so well why our internal solar system has “disappeared”.

Laughlin’s statistics and simulations are based on the Grand Tack Hypothesis – as such, his conclusions cannot be as accurate as this model. But luckily, there are ways to test them.

“Our theory predicts that there should be an anti-correlation between the presence of super-terrestrial planets with short orbital periods and the presence of a giant planet with an orbital period of around a year or more,” said Laughlin. “The validity of this anti-correlation should be testable with the NASA TESS mission, which is currently scheduled to launch in 2017.”

And if Grand Tack turns out to be true, it could have serious implications for humanity’s continued search for exo-Earths. Laughlin’s findings suggest that planets with Earth-like masses and orbits should have “substantial” atmospheres – thick with hydrogen, helium, water vapor, carbon dioxide and nitrogen.

“In the context of our hypothesis, Earth mass planets should be very common,” Laughlin said. “However, truly Earth-like planets, with solid surfaces and atmospheric pressures similar to those we have here on Earth, should be rather rare.”

“I would risk guessing that Earth will indeed turn out to be quite special,” he added. “It will be very interesting to see how this hypothesis holds up over the years and decades to come as we learn more about extrasolar planets.”

Arline J. Mercier