Meteorites Reveal How Old Jupiter Really Is

Jupiter as seen by Hubble. NASA/ESA/HST

Meteorites have been used to unlock many secrets of the early years of the Solar System, but astronomers believe that some of the space rocks can only have been created by Jupiter, giving us a time stamp for the formation of this giant planet.

Researchers looked at a special class of meteorites called CB chondrites, which formed at the very beginning of the Solar System. They contain metallic grains that must have come from vaporized iron and that can only be produced in high-velocity impacts.

These fast collisions cannot be achieved with the expected distribution of material in the asteroid belt. In a paper, published in Science Advances, they propose Jupiter could be the culprit of the accelerated material. However, this idea requires Jupiter to have had its present-day mass within 5 million years of the Solar System forming solid objects, making it just shy of 4.6 billion years old.

"We show that Jupiter would have stirred up the asteroid belt enough to produce the high-impact velocities necessary to form these CB chondrites," said lead author Brandon Johnson, a planetary scientist at Brown University, in a statement. "These meteorites represent the first time the Solar System felt the awesome power of Jupiter."

For Jupiter to be at the right place at the right time, the researchers suggest that the giant planet formed in the outskirts of the Solar System and then migrated inwards where the asteroid belt is located today. This scenario is called the Grand Tack, and it has also been invoked to explain Mars’s diminutive size: Jupiter stole a good chunk of its mass when it was closer.

"When we include the Grand Tack in our model at the time the CB chondrites formed, we get a huge spike in impact velocities in the asteroid belt," co-author Kevin Walsh, from the Southwest Research Institute, added. "The speeds generated in our models are easily fast enough to explain the vaporized iron in CB chondrites."

The Grand Tack produced a collision almost three times faster than the one modeled without Jupiter, but it was a very fleeting affair, lasting at most 500,000 years. After that, astronomers expect that the gravitational pull of the newly formed Saturn pulled Jupiter towards its current orbit, allowing for the (relatively) safe formation of Earth and the other rocky planets.

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