Jupiter’s orbit was a breeding ground for planetesimals, the precursors of planets, asteroids, and comets

The new study, published in the journal The Astrophysical Journal, conducted by researchers at the Max Planck Institute for Solar System Research (MPS) in Germany, identifies a ring-shaped region just outside Jupiter’s orbit as not only an efficient, but also a ‘pluripotent’ planetesimal breeding ground.

Computer simulations show for the first time that over the course of approximately two to four million years, after the birth of the Solar System, Jupiter had already accreted all the matter in its vicinity, carving a gap in the gas and dust disk along its orbit.

When the Solar System formed, a disk of gas and dust orbited the young Sun, and over the course of millions of years, the dust gradually clumped together to form kilometre-sized chunks known as planetesimals.

Some grew into planets, while the rest are considered to be the precursors of today’s asteroids. The researchers assume that this development did not proceed linearly, with different stages of planetesimal development occurring simultaneously, and not every region of the disk offering favourable ‘starting conditions’ for planetesimals.

According to the current understanding, a ring-shaped region of elevated gas pressure formed just outside Jupiter’s orbit, which led to the accumulation of so much dust that it coalesced into small clumps of matter, known as pebbles.

The study highlighted that it was already known that pebbles could grow into planetesimals in such a dust trap at a very early stage. However, it was unclear whether, over long periods of time, this process could produce bodies with very different compositions.

The new study shows that diverse populations of planetesimals can form in dust traps over millions of years. The results thus establish a connection to specific groups of meteorites for the first time.

“For the first time, we have succeeded in accurately reproducing the results of laboratory studies of meteorites using computer simulations of the early Solar System. The meteorites serve, so to speak, as a touchstone for theories of planetary formation”, said MPS Director and cosmochemist Thorsten Kleine.

Meteorites are chunks of rock from space that have crashed onto Earth. Most of them are fragments of planetesimals and have hardly changed since they formed.

Carbonaceous chondrites, stony meteorites that are particularly rich in carbon, are likely to have formed outside Jupiter’s orbit precisely during the simulated time period, as laboratory studies suggest. Based on age and composition, researchers distinguish six groups of carbonaceous chondrites.

While some consist almost exclusively of fine-grained material and crumble apart at the slightest touch, others are significantly more robust. Embedded in the fine-grained material, they contain inclusions that are visible to the naked eye in varying proportions.

Computer simulations spanning all scales

In their simulations, the researchers were able to reproduce the age and composition of the six groups of carbonaceous chondrites. In the calculations, the fine-grained material and the inclusions correspond to two types of material that existed in the early Solar System: fragile, crumbly dust and small clumps of more stable material. The latter had formed at the beginning of the Solar System in some places under the influence of heat and then dispersed.

The models, therefore, take into account the collisions of individual particles (and, as a result, their breaking apart or sticking together) as well as their movements and concentrations within the entire, vast gas disk. For example, both types of particles are drawn from the outer Solar System towards the Sun, albeit at different speeds.

Jupiter’s orbit acts as a more effective barrier for the larger, more stable particles than for the smaller dust. The formation of the first planetesimals also consumes some of the available material.

Over time, as a result of all these effects, both types of matter accumulate in varying proportions in the region outside Jupiter’s orbit, thus creating the conditions for the formation of clearly distinguishable generations of planetesimals. In the first 500,000 years, the proportion of crumbly material initially decreases, only to increase over the next million years.

Thereafter, two distinct populations of planetesimals emerge, consisting either almost exclusively of crumbly material or stable material.

Based on their calculations, the researchers believe that, at an earlier stage, meteorite types other than carbonaceous chondrites may also have formed in the dust trap beyond Jupiter. “There is strong evidence that dust traps were the preferred birthplace of planetesimals in our Solar System,” concluded Joanna Drążkowska, Head of Lise Meitner Group at MPS.