Jupiter Used to Be Four Times Farther from the Sun, Study Claims

New research explains a strange feature of Jupiter's nearby asteroids by suggesting the planet started out life much farther from home.

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NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

Astronomers have about the planet Jupiter: According to a simulation, the giant planet spent much of its early life roaming throughout the solar system and settled into its current orbit only after drifting in from around four times further from the sun than it is now.

Over the past two decades, scientists have discovered enough planets around other stars to offer a clearer picture of the average solar system, and to reveal the ways in which our own solar system is really weird. For instance, most systems have gas giant planets, but those "hot Jupiters" tend to orbit very close to their host stars. That makes our solar system an outlier. All our system’s gas giants orbit in the outer solar system, while the inner region is reserved for rocky planets like our own.

But according to a new simulation, our home system is even weirder than we thought.

One of the outstanding mysteries of our solar system involves the Trojan asteroids. The Trojans are a group of asteroids that circle the Sun in the same orbit as Jupiter but at a distance either in front of or behind the giant planet. These two groups should be pretty much identical, except the leading group of Trojans has about 50 percent more asteroids.

According to by researchers at Lund University, the only way that discrepancy could have happened is if Jupiter wasn’t always located where it is today. The researchers’ simulations suggest Jupiter started out as an Earth-sized planet about four times farther away than it is today. Over hundreds of thousands of years, Jupiter slowly migrated closer to our Sun until it ended up in its present location.

As the giant planet started drifting closer to the inner solar system, it began picking up stray asteroids. Those asteroids eventually became the Trojans. Because of the way in which Jupiter migrated, it ended up collecting more asteroids in front than behind. That’s why this strange discrepancy exists.

The Lund researchers say Jupiter spent about 700,000 years in this roaming period, before settling down in its current orbit about three million years after it formed. It has then spent the past four billion years or so living a nice life in its own section of the solar system, shared with a bunch of Trojan asteroids.

It’s possible that the other giant planets had a similar early phase, which means all of our giant planets could have originated much farther away from the Sun than they currently reside. If so, scientists would have to rethink a lot of what they thought they knew about our solar system’s formation.

Even though this changes how we view our own solar system, it doesn't bring it more in line with all the other ones out there. If anything, it makes it weirder. Are we actually the odd solar system out? Or are there other solar systems like ours out there waiting to be discovered? Whenever science answer one question, the universe provides us with more.

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