Astronomers have long tried to explain how the basic ingredients of planets and comets form and spread through young solar systems. Now, an international research team led by scientists in South Korea says it has directly observed a key part of that process—capturing how a newborn star’s intermittent growth spurts can create and help move the building blocks of rocky worlds.
South Korea’s Ministry of Science and ICT announced that the team, led by Professor Jeong-Eun Lee of Seoul National University’s Department of Physics and Astronomy, has identified how crystalline silicates form and are transported during the earliest stages of star formation. The findings were published in Nature on Jan. 21 (local time).
Crystalline silicates are a major component of planetary systems, including the material that ends up in Earth-like planets and comets. The result is being described as a significant step toward solving a decades-old puzzle in astronomy.
How Stars and Planetary Systems Take Shape
Stars like the Sun form when cold molecular clouds in space collapse under gravity. These clouds are made up of about 99% gas and 1% dust. Before a star begins generating energy through nuclear fusion, it exists as a “protostar”—a young object still pulling in surrounding material.
As a protostar grows, the remaining cloud material settles into a flattened, rotating structure known as a protoplanetary disk. Over time, dust and gas inside this disk clump together, eventually forming planets, asteroids, and comets.
“Since most stars form a disk, it is common for planetary systems like our solar system to exist,” Professor Lee said.
Why Inner and Outer Planets Form Differently
Conditions inside a protoplanetary disk vary widely depending on distance from the star.
Closer to the protostar, the environment is hotter and dominated by dry dust that does not easily stick together, creating conditions favorable for forming smaller rocky planets like Mercury and Earth.
Farther out, colder temperatures allow ice to coat dust grains, making them more likely to clump into larger bodies that can grow into gas giants like Jupiter.
A Protostar That Eats in Bursts, Not Steadily
The team’s work focuses on what happens very close to the protostar, where temperatures can become extreme.
In the innermost disk, dust particles can be destroyed by heat. The remaining gas then flows into the protostar along magnetic field lines. But this process is not smooth. Instead, protostars often grow through “episodic accretion”—alternating between active feeding periods and quieter phases.
During an outburst, a protostar rapidly pulls in a large amount of material. This triggers a strong shock at the star’s surface, making it brighter and heating nearby regions of the disk. During quieter periods, the protostar is dimmer and cooler.
In effect, the environment where planets begin to form changes depending on the protostar’s “eating habits.”
The Mystery of Crystalline Silicates
One of the biggest unanswered questions has been the origin of crystalline silicates, which are found in many planetary systems and are considered essential ingredients for terrestrial planets and comets.
Crystalline silicates require temperatures of roughly 1,100°F (600°C) or higher to form. But the molecular clouds where stars are born are extremely cold—around minus 436°F (minus 260°C). That gap has made it difficult to explain how crystalline silicates could appear so early, and how they end up far from the star in regions where comets form.
JWST Observations of EC 53 Reveal Crystals Forming During Outbursts
To investigate, the researchers targeted a protostar known as EC 53, located in the direction of the Serpens constellation. EC 53 is known for a repeating brightness cycle of about 1.5 years, making it an ideal natural laboratory for studying episodic accretion.
Using NASA’s James Webb Space Telescope (JWST), the team analyzed the spectrum of light from the material surrounding EC 53 when it was at its brightest and dimmest. This allowed them to map the distribution of key materials in the disk.
Their analysis confirmed the presence of crystalline silicates during the outburst phase—marking the first time the material has been directly detected forming under these conditions.
The researchers credited JWST’s sensitivity for making the detection possible, since the silicate signals are faint and difficult to measure with previous instruments.
How Do Crystals Reach the Outer Solar System?
Even with intense bursts of heating, a protostar cannot warm the entire disk out to the distant regions where comets form—comparable to beyond Neptune’s orbit in our own Solar System. That raises a second major question: how can crystalline silicates, formed close to the star—roughly within the distance from the Sun to Earth—end up far beyond the outer planets?
The “Disk Wind” Explanation
The team says the answer lies in a mechanism known as a “disk wind.”
A disk wind is an outflow of material that streams away from the disk, moving roughly perpendicular to its plane. In this model, crystalline silicates formed in the hot inner disk can be lifted and carried outward by the wind, eventually reaching colder, more distant regions.
Observations of EC 53 revealed outflows moving at different speeds, supporting the idea that a disk wind is present and capable of transporting material across the developing planetary system.
What the Discovery Could Mean for Exoplanets
By linking episodic accretion, crystal formation, and disk winds in a single observational framework, the researchers say they have established a key indicator for explaining how planetary systems—including exoplanet systems—can develop their basic solid materials.
“We have established an important indicator for explaining the mechanism by which the Solar System and exoplanetary systems are formed,” Professor Lee said. “This is a case where experience accumulated over a long period has led to a scientific discovery.”
Next Steps: Finding More Protostars to Study
The team plans to expand the work by identifying and monitoring additional protostars using the SPHEREx space telescope, which launched in March last year and is designed to survey large areas of the sky.
SPHEREx can track brightness changes across many objects roughly every six months. When it identifies a promising target, astronomers can then pursue more detailed follow-up observations with JWST.
Securing JWST time remains highly competitive, with proposals facing competition rates of about 10 to 1 during the period when Professor Lee’s team participated. The team obtained JWST observation time twice for EC 53.
“We were allocated the observation time because we had a model and information about protostars built from past data, including predicted temperatures for the EC 53 observation,” Professor Lee said.
Conclusion
By catching a young star in the act of rapid feeding, astronomers have gained rare, direct evidence of how crystalline silicates—essential raw material for rocky planets and comets—can form and spread through a developing solar system. The findings strengthen a long-theorized picture of planetary origins and offer a clearer path for understanding how systems like our own may take shape across the Milky Way.