About 4.6 billion years ago, the young Sun was surrounded by a massive disk of gas and dust. Over time, tiny dust grains collided and stuck together, eventually forming larger rocky bodies called planetesimals, the building blocks of planets and asteroids. But scientists believe this process was far from simple. Different regions of the early Solar System likely evolved under very different conditions, and multiple stages of planet formation may have happened at the same time.
Now, researchers from the Max Planck Institute for Solar System Research (MPS) in Germany say they have identified one of the Solar System’s most important planet-forming regions. According to a new study published in The Astrophysical Journal, a ring-shaped area just beyond Jupiter’s orbit acted as both an efficient and remarkably versatile “breeding ground” for planetesimals.
Using computer simulations, the team found that this region produced planetesimals with very different compositions over a span of roughly two million years.
“Different types of planetesimals apparently formed in the same region of the early dust and gas disk, only at different times. The region just outside Jupiter’s orbit offered excellent conditions for this,” said Joanna Drążkowska, head of the Lise Meitner Group on planet formation.
How Jupiter Created a Cosmic Dust Trap
The study focused on a period between about two and four million years after the Solar System formed. By then, Jupiter had already gathered most of the nearby material around its orbit, creating a gap in the surrounding disk of gas and dust.
Scientists believe this process also created a ring of higher gas pressure just beyond Jupiter. That pressure trapped large amounts of dust, allowing small clumps known as pebbles to collect there. Earlier studies had already suggested that such “dust traps” could help planetesimals form quickly during the Solar System’s early stages.
What remained unclear was whether these dust traps could continue producing very different types of bodies over long periods of time. The new simulations suggest they could.
The researchers showed that diverse populations of planetesimals likely formed in this same region over millions of years. Their findings also connect these simulated objects to known groups of meteorites found on Earth.
“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 Preserve Clues to the Solar System’s Past
Meteorites are fragments of space rock that survive their journey through Earth’s atmosphere and land on the planet’s surface. Many are believed to be pieces of ancient planetesimals that have changed very little since the Solar System’s earliest days.
The researchers focused especially on carbonaceous chondrites, a type of meteorite rich in carbon. Laboratory studies suggest these meteorites formed beyond Jupiter during the same time period explored in the simulations.
Scientists divide carbonaceous chondrites into six groups based on their age and composition. Some are fragile and made mostly of fine-grained material, while others are stronger and contain visible inclusions embedded within the finer material.
In the new simulations, those two components matched two kinds of matter thought to exist in the early Solar System. One consisted of fragile, dusty material, while the other was made of sturdier clumps that formed very early in hotter regions before spreading throughout the disk.
“For our simulations, it was crucial to model the behavior and interaction of both materials on both small and large scales,” said Nerea Gurrutxaga, PhD student at the MPS and first author of the paper.
Simulations Reveal Multiple Generations of Space Rocks
The team’s models tracked both microscopic particle collisions and large-scale movement throughout the enormous gas disk. Particles could break apart, stick together, drift toward the Sun, or become trapped in certain regions.
The simulations showed that Jupiter acted as a stronger barrier for larger and sturdier particles than for smaller dust grains. At the same time, the formation of new planetesimals steadily consumed some of the available material.
As millions of years passed, these combined effects caused the two types of material to gather in different proportions beyond Jupiter’s orbit. That changing balance eventually led to the formation of clearly distinct generations of planetesimals.
During the first 500,000 years, the amount of crumbly material dropped before rising again over the following million years. Later, two separate populations of planetesimals appeared, one made mostly of fragile material and another dominated by more stable matter.
Based on their results, the researchers suspect that additional meteorite types besides carbonaceous chondrites may also have formed in the same dust trap during even earlier stages of Solar System history.
“There is strong evidence that dust traps were the preferred birthplace of planetesimals in our Solar System,” said Joanna Drążkowska.