By analyzing in meteorites, a team of scientists has determined that Jupiter is the oldest planet in the solar system.
Measurement of the meteorites’ chemical signatures reveals their ages as well as their origins in one of two separate meteorite groups.
About one million years after the solar system formed, meteorites’ precursor asteroids divided into two separate groups from two distinct parts of the solar nebula. They remained separate for about three million years.
Jupiter, whose rocky core came together less than a million years after the solar system’s formation, likely divided the meteorite population into these two groups–one between Jupiter and the Sun and the other beyond Jupiter’s orbit.
Thomas S. Kruijer of the Lawrence Livermore National Laboratory in California and co-author of a study published in said Jupiter’s gravity was strong enough to keep meteorites from crossing its orbit when the solar system was just a million years old.
“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,” Kruijer explained.
“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.”
In just a million years, Jupiter’s core to 20 Earth masses. Within three to four million years, it grew to 50 Earth masses.
No meteorite samples from Jupiter exist, which is why the scientists studied meteorites which originated as parts of asteroids.
After the solar system formed from a disc of gas and dust 4.6 billion years ago, the gas giant planets were the first to appear. They grew by accumulating gas from the protoplanetary disc onto their large cores.
This means their cores formed while the protoplanetary disc or solar nebula, composed of gases circling the young Sun, was still present.
Gases in the disc are believed to have dissipated about 10 million years ago.
Computer models show Jupiter was the first planet to form, but they have not successfully narrowed down when that happened.
Currently more than 30 Earth masses, Jupiter accreted material from the protoplanetary disc before the solar system’s other planets formed.
Some scientists believe Jupiter subsequently migrated inward toward the Sun, only to be pulled back by Saturn following that planet’s formation.
The motion between the two planets could have reunited the two groups of asteroids back into a single population, where they remain today in the belt between Mars and Jupiter.