Using the James Webb Space Telescope (JWST), astronomers have studied 72 young, sun-like stars. As a result, they found that forming planets is a real race against time.
This is because the material that serves as the building blocks for planets is constantly escaping the swirling platters of gas and dust, or protoplanetary disks, that wrap around infant stars. Some types of planets may find their formation window closing sooner than others.
The team’s research represents the most in-depth investigation yet into how matter escapes these protoplanetary disks and how this escape gives rise to different stages of planet formation around sun-like stars. All in all, the study helps paint a better picture of how and why our solar system took the shape it did around the infant sun around 4.6 billion years ago.
“Gas giants like Jupiter must assemble their massive atmospheres while the disk is still substantial enough to supply them, before winds and jets carry that raw material away into space,” team leader Naman Bajaj from the University of Arizona said in a statement.
An ill wind blows around infant stars
The team conducted its research using data collected by the JWST’s Mid-Infrared Instrument (MIRI). The scientists tracked matter loss by following the movements of molecular hydrogen, one of the most common molecules in protoplanetary disks. Each of the stars involved in the investigation represented a different stage in the early life of a star system. That meant putting these snapshots together allowed the researchers to create a “movie” detailing the early life of a planetary system.
One of the most important findings of this approach is the mechanisms for material loss from protoplanetary disks seem to evolve and switch dominance as an infant star ages.
This is important because gas giants like Jupiter and Saturn have vast atmospheres. They thus require more raw material to form than smaller rocky worlds like Earth do. Understanding matter loss allows scientists to determine at what stages of protoplanetary disk evolution gas giants can form.
“What is exciting about this study is that we can now see, across a large sample of young systems, how the mechanisms that remove gas from planet-forming disks change with time,” team member Uma Gorti from the SETI Institute said in the statement. “Disk dispersal sets a fundamental clock for planet formation: once the gas is gone, the opportunity to build gas-rich planets is essentially over.”
The researchers found that early in the evolution of protoplanetary disks, powerful, magnetically driven jets and winds dominate mass loss. These jets and winds are powered by magnetic fields that weave through protoplanetary disks.
Later, as the disk thins and starlight can pass through it more easily, these winds and jets weaken, and magnetic processes are dominated by high-energy radiation from the infant star ionizing gas and blowing it into space. The latter process is called photoevaporation.
All this reveals there is no one single process responsible for stripping planet-forming material from around infant stars. The research also demonstrates the JWST is more than capable of studying the dispersal of gas and dust around individual infant stars.
The next step for the team is to discover just how much material these different mechanisms shift. The scientists could also look into the areas of the disks in which the mechanisms studied operate. Down the line, this will help develop a model to reveal just how rapidly planet-formation is shut off — and in which regions of a protoplanetary disk different types of planets are most likely to form.
The team’s research was published on Tuesday (August 25) in The Astronomical Journal.
