Ancient meteorites tap Jupiter as oldest planet in solar system

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 coauthor Thomas Kruijer, a researcher at the Lawrence Livermore National Laboratory in California.

To probe the planet’s creation, experts sampled extraterrestrial material that landed on Earth — ancient meteorites.

The 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 — 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.

The new study supports the idea of a firstborn Jupiter. When Jupiter formed, the growing planet swept up a great swath of gas and dust as it circled the sun.

What’s more, it acted as a barrier to shield the inner solar system from wayward meteorites. When the solar system was about 1 million years old, Jupiter’s gravity was strong enough to prevent rocks from crossing beyond its orbit, like a club bouncer who forces latecomers to wait on the sidewalk.

“At about 1 million years you have Jupiter getting big enough to cut off the inner solar system from the outer solar system,” said Brown University’s Brandon Johnson, a planetary scientist who was not involved with the new research.

Then, when the solar system was around 4 million years old, Jupiter grew to about 50 Earth masses and headed toward the sun.