A study at Lawrence Livermore National Laboratory [LLNL] has confirmed that Jupiter, the largest planet in our solar system, is also the oldest. Looking at tungsten and molybdenum isotopes on iron meteorites, the LLNL team in collaboration with Institut fur Planetologie at the University of Munster in Germany, 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 explosion of a nearby star called a supernova 4600 million years ago that led to the formation of Solar System.
“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,” explained Thomas Kruijer, lead author of the paper, in a news release. “Jupiter is the oldest planet 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.”
The most impressive feature about Jupiter is its sheer size which had an immense effect on the dynamics of the solar accretion disc. To understanding how the solar system evolved toward its present-day architecture, it’s important to know the age of Jupiter. Although models predict that Jupiter formed relatively early, the team says until now, its formation has never been dated.
In the study, the team used isotope signatures of meteorites (which are derived from asteroids) to probe Jupiter’s creation as they did not have any samples from Jupiter, in contrast to other bodies like the Earth, Mars, the moon and asteroid. So through isotope analyses of meteorites, they were able to confirm that Jupiter’s solid core formed within only about 1 million years after the solar system formation, making it the oldest planet. Researchers further noted that through its formation, Jupiter acted as a barrier against inward transport of material across the disc, potentially explaining why our solar system does not have any super-Earths (an extrasolar planet with a mass higher than Earth’s). They also found that Jupiter’s core grew to about 20 Earth masses, by the time the solar system was about 1 million years old, followed by a more prolonged growth to 50 Earth masses when the solar system was at least 3-4 million years old.
Since gas-giant planets such as Jupiter and Saturn involved the growth of large solid cores of about 10 to 20 Earth masses, followed by the accumulation of gas onto these cores, the researchers’ conclusion was that the planets’ cores must have formed before dissipation of the solar nebula — the gaseous circumstellar disc surrounding the young sun — which likely occurred between 1 million years and 10 million years after the solar system formed. In the work, the team did confirm the earlier theories but were able to date Jupiter much more precisely within 1 million years using the isotopic signatures of meteorites.
“Our measurements show that the growth of Jupiter can be dated using the distinct genetic heritage and formation times of meteorites,” Kruijer added.