Jupiter Experienced Some Real Growing Pains When Forming, Study Suggests

Jupiter’s southern hemisphere photographed by NASA’s Juno spacecraft. NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/ Seán Doran

We know quite a lot about Jupiter. It's the largest planet in the Solar System and it plays a role in regulating how asteroids and comets get closer to the Sun, a behavior that protects the inner planets. The formation of the planet was thought to be understood too, but new evidence suggests that it might have happened in a different way – in growth spurts.

The new research has provided an explanation for some relics from the early Solar System that have been difficult to explain otherwise, as well as provide a more complex and intriguing formation to the gas giant.

It all started last year when new data revealed the presence in the Solar System of two distinct population of meteorites. Jupiter enters the picture because researchers suspected that one group of meteorites formed before the gas giant and the other one formed afterwards. This backdated the formation of Jupiter and extended its formation time as well.

"How could it have taken two million years for Jupiter to grow from 20 to 50 Earth masses?" co-author Julia Venturini, from the ETH Zürich asked in a statement. "That seemed much too long. That was the triggering question that motivated our study."

Venturini and colleagues gathered scientists from different fields together and quickly had a detailed approach to answering the question. 

Their study, published in Nature Astronomy, has now revealed Jupiter experienced three distinct growth phases over the few first million years of the Solar System. The planet’s embryo was initially formed quite quickly by centimeter-sized pebbles, which created the original core over the first million years or so. Then for 2 million years, it followed with a slower accretion of planetesimals, a few kilometers across in size, until it reached a mass of about 50 times the Earth. The third phase was the accretion of gas, which continued until Jupiter became 300 times the size of our planet.

"Especially interesting is that it is not the same kind of bodies that bring mass and energy [to the formation of the planet]," first author Yann Alibert, from the Swiss National Centre of Competence in Research at the University of Bern and Zürich, added. "During the first stage, the pebbles brought the mass. In the second phase, the planetesimals also added a bit of mass, but what is more important, they brought energy."

They were able to show that pebbles are key to the first stage build-up of the gas giant but it’s the heat delivered by the planetesimal that slows down accretion of gas long enough to match the meteorite findings.

This model has other interesting consequences. It is more likely to form medium-size gas giants rather than large ones like Jupiter, suggesting that this is also how Uranus and Neptune might have formed.

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