Jupiter Might Be The Oldest Planet In The Solar System

Lookin' good, old timer. NASA/SwRI/MSSS/Gerald Eichstädt/Seán Doran

Not content with simply being the biggest planet in the Solar System, Jupiter may have now cemented itself as the oldest too based on new evidence.

Published in the Proceedings of the National Academy of Sciences, a study led by the University of Munster in Germany looked at the ages of iron meteorites. Researchers found that some originated from two “reservoirs” 1 million and 3 to 4 million years, respectively, after the Solar System formed (4.6 billion years ago). And Jupiter appears to be the cause of that difference, pushing back its age.

"The most plausible mechanism for this efficient separation is the formation of Jupiter,” said Thomas Kruijer, lead author of the paper, in a statement. Jupiter would have carved out a gap in the disk of dust and gas that surrounded our young Sun, which prevented material from these two reservoirs mixing.

In order to create that gap, Jupiter needed to have reached a certain size. According to the researchers, its core would have been 20 times the mass of Earth (today it is 318 times as massive) just 1 million years after the Solar System formed. It took up to 10 million years for the other gas giants to form, and up to 100 million years for the rocky planets to take shape.

"Jupiter is the oldest planet in the Solar System, and its solid core formed well before the solar nebula gas dissipated, consistent with the core accretion model for giant planet formation," Kruijer said.

This finding was made by looking at tungsten and molybdenum isotopes on iron meteorites that had fallen to Earth. There were 19 studied in total, which came from small asteroids that formed around the same time as Jupiter.

The cores of gas giants like Jupiter must have formed before the gas and dust around our Sun dissipated. They gathered this onto their cores, growing into the gas giants we see today. This puts their formation at between 1 and 10 million years after the Solar System’s formation, when the nebula is thought to have vanished.

This study puts Jupiter right at the start of that process, but it's unclear if the other gas giants could have formed relatively early too. If Jupiter had a big part to play in our Solar System’s formation, possibly sweeping through it and kicking out another planet, known as the Grand Tack model, that may influence things.

"If the so-called Grand Tack model is correct, then Saturn may have formed around 4 million years [into the] Solar System's history," Kruijer told IFLScience.

For now, Jupiter looks to be king of the planets. With NASA’s Juno spacecraft currently in orbit, scientists are hoping to find out more about its core and its origins, too, in the near future.

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