Key Insights into Rapid Formation of Giant Planets

Key Insights into Rapid Formation of Giant Planets
by Robert Schreiber
Berlin, Germany (SPX) Aug 02, 2024

A team of researchers at LMU has developed a novel model that explains the formation of giant planets like Jupiter. This model provides deeper insights into planetary formation processes and may broaden our understanding of planetary systems. Our solar system is familiar: the Sun at the center; rocky planets Mercury, Venus, Earth, and Mars; the asteroid belt; gas giants Jupiter and Saturn; ice giants Uranus and Neptune; and the Kuiper belt with its comets.

Despite this familiarity, our understanding of the formation of our solar system is still evolving. Previous theories suggested that giant planets formed through collisions and accumulations of asteroid-like bodies, known as planetesimals, followed by the accretion of gas over millions of years. However, these theories fail to explain the presence of gas giants far from their stars and the formation of Uranus and Neptune.

From Dust to Giant Planets
Astrophysicists from LMU, the ORIGINS cluster, and MPS have created the first model that incorporates all the necessary physical processes in planet formation. This model demonstrates that annular perturbations in protoplanetary disks, called substructures, can initiate the rapid formation of multiple gas giants. The study's findings align with the latest observations and suggest that giant planet formation may be more efficient and quicker than previously thought.

The researchers' model shows how millimeter-sized dust particles accumulate aerodynamically in the turbulent gas disk. This initial perturbation traps dust, preventing it from drifting toward the star. This accumulation facilitates planet growth, as a substantial amount of "building material" is available in a compact area under favorable conditions.

"When a planet gets large enough to influence the gas disk, this leads to renewed dust enrichment farther out in the disk," explains Til Birnstiel, Professor of Theoretical Astrophysics at LMU and member of the ORIGINS Cluster of Excellence. "In the process, the planet drives the dust - like a sheepdog chasing its herd - into the area outside its own orbit." The process begins anew, from inside to outside, and another giant planet can form. "This is the first time a simulation has traced the process whereby fine dust grows into giant planets," observes Tommy Chi Ho Lau, lead author of the study and doctoral candidate at LMU.

Variety of Gas Giants in Our and Other Solar Systems
In our solar system, gas giants range from around 5 astronomical units (au) (Jupiter) to 30 au (Neptune) from the Sun. For comparison, Earth is approximately 150 million kilometers from the Sun, equivalent to 1 au.

The study shows that in other planetary systems, a perturbation could initiate the process at much larger distances and still occur very rapidly. Systems with gas giants located beyond 200 au have been frequently observed in recent years by the ALMA radio observatory. The model also explains why our solar system seemingly stopped forming additional planets after Neptune: the building material was simply depleted.

The results of the study match current observations of young planetary systems that have pronounced substructures in their disks. These substructures play a decisive role in planet formation. The study indicates that the formation of giant planets and gas giants proceeds with greater efficiency and speed than previously assumed. These new insights could refine our understanding of the origin and development of the giant planets in our solar system and explain the diversity of observed planetary systems.

Research Report:Sequential giant planet formation initiated by disc substructure