How Jupiter split the asteroid belt in half shows its great age



Jupiter was huge when the solar system was still young

NASA, ESA and A. Simon (NASA Goddard)

It’s a hell of a bowling ball. A comparison of meteorites revealed that, in his youth, Jupiter made his way through the solar system that separated space rocks into two distinct families. And it did it less than a million years after the dawn of the solar system, so Jupiter was already huge at least 4 billion years ago.

Meteorites found on Earth have different proportions of isotopes of the elements they contain, depending on whether they originate from a rock that originated inside or outside of Jupiter’s orbit. Differences between the rocks are visible even in the chipped planetesimals that formed within the million years of the formation of the solar system, so they must have separated before that.

To have been large enough to carve out such a space in the protoplanetary disk – a dense cloud of gas and dust orbiting the newly formed sun – Jupiter’s core would have had to be about 20 times the mass of Earth. This new meteorite analysis, by Thomas Kruijer of the University of Münster in Germany and his colleagues, indicates that Jupiter must have reached this size during the solar system’s first million years.

Young people who divide

Jupiter is believed to have formed like other gas giants: its rocky core came first, then it gradually accumulated more matter from the dust and gas around the sun, and then acquired its gaseous envelope.

Kruijer’s team analyzed 19 iron meteorites found on Earth that came from small bodies that formed alongside Jupiter. The isotopes of elements in rocks that formed inside Jupiter’s orbit had more elements of the type that slowly accumulate in stars, while those further in the solar system were enriched. into heavy elements that form more quickly in high energy situations. .

“These isotopic labels are carried by very small grains of dust,” explains Francis Nimmo of the University of California at Santa Cruz. “Somehow you have to create a situation where these little specks of dust get mixed around one part of the solar system but not the other.”

Some of the isotopes in meteorites outside of Jupiter’s orbit are over half a million years younger, meaning that after Jupiter split the disk, they couldn’t jump up. space in the interior area.

“We need more evidence that this is where these two classes of meteorites form – one inward and one outward,” says Jonathan Lunine of Cornell University in New York. “But it is a very nice measure.”


The work supports one of the main theories of the early solar system – the big tip hypothesis. This assumes that Jupiter was born a few million years before Saturn and that its enormous mass was pulled towards the sun. Once Saturn formed, however, its gravity moved Jupiter from the edge of stellar destruction to the outer solar system.

These two drifts through the solar system meant that Jupiter crashed twice through the asteroid belt, mixing the two types of objects in the asteroid belt, leaving behind the well-mixed objects that we see. today.

“What’s really striking is that the big tack was offered before anyone knew about this isotopic labeling, but the isotopes seem to go really well with the big tack,” says Nimmo. “It’s pretty powerful.”

“It’s a really cool story,” says Nimmo, “and I think it’s probably true. “

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073 / pnas.1704461114

Read more: Mars is so small because Jupiter rocked its formation

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