Jupiter formed in a geologic blink. Its rocky core coalesced less than a million years after the beginning of our solar system, scientists reported Monday in the Proceedings of the National Academy of Sciences. Within another 2 million or 3 million years, that core grew to 50 times the mass of Earth.
Scientists have previously built computer models of the birth of Jupiter. But this study “is the first time that we can say something about Jupiter based on measurements done in the lab,” said study co-author Thomas Kruijer, a researcher at the Lawrence Livermore National Laboratory in California.
To probe the planet’s creation, experts sampled extraterrestrial material that happens to land on Earth — ancient meteorites. Our solar system began as a disk of dust and gas 4.6 billion years ago. Of the planets, first came the gas giants, followed by such rock-and-metal terrestrial worlds as Earth. Jupiter is the biggest of the brood. Despite being mostly gas by bulk, it’s more than 300 times the mass of Earth. For that reason, astronomers suspect the planet was the oldest, able to scoop up more material out of the disk before its younger siblings appeared.
By looking at tungsten and molybdenum isotopes on iron meteorites, the team, made up of scientists from Lawrence Livermore National Laboratory found that meteorites are made up from two genetically distinct nebular reservoirs that coexisted but remained separated between 1 million and 3-4 million years after the solar system formed.
“The most plausible mechanism for this efficient separation is the formation of Jupiter, opening a gap in the disc (a plane of gas and dust from stars) and preventing the exchange of material between the two reservoirs,” said Thomas Kruijer, lead author of the paper appearing in the June 12 online issue of Proceedings of the National Academy of Sciences.
Formerly at the University of Munster, Kruijer is now at LLNL. “Jupiter is the oldest planets 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.”
Jupiter is the most massive planet in the solar system and its presence had an immense effect on the dynamics of the solar accretion disc. Knowing the age of Jupiter is key to understanding how the solar system evolved toward its present-day architecture. Although models predict that Jupiter formed relatively early, until now, its formation has never been dated. The new study adds evidence to the idea that Jupiter temporarily split the population of meteorites in the solar system in two: those between Jupiter and the sun, and those beyond Jupiter.
If a pair of inner and outer space rocks landed in your front yard, and you picked them up after they cooled down and the dust settled, you wouldn’t be able to spot a difference. But Kruijer and his colleagues can measure specific chemical signatures in meteorites — which reveal not only the rocks’ age but which of the two groups they once belonged to. It was only recently that technological advances allowed scientists to measure the differences in the two, Kruijer said.
The meteorite groups separated around 1 million years after the solar system formed, and stayed apart until about 4 million years post-formation, according to the new analysis. Crucially, the two populations existed simultaneously for a few million years. Most meteorites derive from small bodies located in the main asteroid belt between Mars and Jupiter. Originally, these bodies probably formed at a much wider range of heliocentric distances, as suggested by the distinct chemical and isotopic compositions of meteorites and by dynamical models, indicating that the gravitational influence of the gas giants led to the scattering of small bodies into the asteroid belt.
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