Why are minerals that form only in hot environments found inside cold comets? A domestic research team has found a clue that could solve a question that has long vexed the astronomy community.
A team led by Professor Lee Jeong-eun of the Department of Physics and Astronomy at Seoul National University, together with an international team that includes the Korea Astronomy and Space Science Institute (KASI), said it proved that silicates crystallize during the "outburst phase," when a protostar, the stage just before a star is born, suddenly brightens, and that crystalline silicates formed in this way can ride the wind outward to the region where comets form. The findings were published in Nature on the 22nd.
Silicates make up about 90% of Earth's crustal material and are considered key components of terrestrial planets and comets. In particular, "crystalline silicates," which have a regular crystal structure, have been known to form only at high temperatures of 600 degrees or more. But crystalline silicates have been found in comets in the extremely cold outer solar system, leaving the question for a long time of "how did materials formed at high temperatures travel so far outward?"
The team focused on the protostar EC 53 in the Serpens nebula. This object varies in brightness on a roughly 18-month cycle, allowing a clear distinction between outburst (bright) and quiescent (dim) phases. The team, securing observation time on the James Webb Space Telescope (JWST), the only one in Korea to do so, observed both phases of EC 53 in Oct. 2023 and May 2024, respectively.
As a result, they confirmed that data for crystalline minerals were detected only during the outburst phase. The outburst phase here refers to the moment when the process of a protostar accreting material from its surrounding disk suddenly intensifies. Stars are born as molecular clouds of gas and dust clump together under gravity, and when a protostar forms at the center, a flattened disk forms around it. The protostar draws in material from this disk to grow in size. In this process, shocks at the protostar's surface increase and energy is released all at once, causing the star to brighten rapidly. The team saw this moment as disrupting the disk's chemical state and triggering silicate crystallization.
Furthermore, the team showed that crystalline silicates generated in the inner disk can be transported to the cold outer regions by "disk winds." Disk winds are outward-blowing winds from the disk surface, and the team indirectly confirmed the material flows created by the winds. The work offers a clue to explain why crystalline silicates are found in comets.
The reason this result is drawing particular attention is that it solved two riddles—silicate crystallization and transport—at once. Hints had been captured in past Spitzer Space Telescope observations, but limits in resolution and sensitivity made it difficult to resolve the disk and surrounding structures in detail.
At a briefing on the 19th, Professor Lee said, "Thanks to JWST collecting light with a much larger mirror and having higher resolution, we were able to separately observe even the outflow of small structures around the protostar."
The team said it plans to increase the sample size to verify generality. The approach is to use all-sky survey space telescopes that scan the entire sky periodically, such as SPHEREx, to find candidate protostars that suddenly brighten, and then conduct precise follow-up observations with JWST.
Lee added, "The sun also went through a protostar phase before it was born, and the planets, asteroids, and comets of the solar system were formed in the disk around the sun. Because the sun may have undergone a process like EC 53, these observations could provide important clues to understanding not only the solar system but also how planetary systems around other stars form."
References
Nature(2026), DOI: https://doi.org/10.1038/s41586-025-09939-3