Instability at the Beginning of the Solar System – Implications for Mysterious
All stars, including our sun, are born from a cloud of dust and gas. This cloud can also seed planets that will orbit the star. Credit: NASA/JPL-Caltech
The Instability at the Beginning of the Solar System
A new explanation for why our solar system is the way it is — and why others are, too.
Seth Jacobson of Michigan State University and colleagues in China and France have unveiled a new theory that could help solve a galactic mystery of how our solar system evolved. Specifically, how did the gas giants —
The findings have ramifications for how terrestrial planets like Earth developed, as well as the possibility that a fifth gas giant planet lurks 50 billion miles out into the distance.
“Our solar system hasn’t always looked the way that it does today. Over its history, the orbits of the planets have changed radically,” said Jacobson, an assistant professor in the College of Natural Science’s Department of Earth and Environmental Sciences. “But we can figure out what’s happened.”
An artist’s rendering shows a hypothetical early solar system with a young star clearing a path in the gas and dust left over from its formation. This clearing action would affect the orbits of gas giants orbiting the star. Credit: NASA/JPL-Caltech/T. Pyle (SSC)
The research, published in the journal Nature on April 27, 2022, offers an explanation for what happened to gas giants in other solar systems and ours.
It’s a Nice model
Massive, whirling clouds of cosmic gas and dust give birth to stars. The early solar system was still filled with a primordial disk of gas when our sun ignited, and it played an important role in the formation and evolution of the planets, including the gas giants.
In the late 20th century, scientists began to believe that the gas giants initially circled the sun in neat, compact, uniformly spaced orbits. Jupiter, Saturn, and the others, however, have long settled into orbits that are relatively oblong, misaligned, and spread apart.
MSU Assistant Professor Seth Jacobson
So the question for researchers now is, why?
In 2005, an international team of scientists proposed an answer to that question in a trio of landmark Nature papers. The solution was originally developed in Nice, France and is known as the Nice model. It posits that there was an instability among these planets, a chaotic set of gravitational interactions that ultimately set them on their current paths.
“This was a tectonic shift in how people thought about the early solar system,” Jacobson said.
The Nice model remains a leading explanation, but over the past 17 years, scientists have found new questions to ask about what triggers the Nice model instability.
For example, it was originally thought that the gas giant instability took place hundreds of millions of years after the dispersal of that primordial gas disk that birthed the solar system. But newer evidence, including some found in moon rocks retrieved by the Apollo missions, suggests it happened more quickly. That also raises new questions about how the interior solar system that’s home to Earth evolved.
Sean Raymond, an astronomer at the University of Bordeaux.
Working with Beibei Liu from Zhejiang University in China and Sean Raymond from the University of Bordeaux in France, Jacobson has helped find a fix that has to do with how the instability started. The team has proposed a new trigger.
“I think our new idea could really relax a lot of tensions in the field because what we’ve proposed is a very natural answer to when did the giant planet instability occur,” Jacobson said.
The new trigger
The idea started with a conversation Raymond and Jacobsen had back in 2019. They theorized the gas giants may have been set on their current paths because of how the primordial gas disk evaporated. That could explain how the…
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