Tracing the Fate of Crystalline Dust in Protoplanetary Disks with JWST

Jun. 4, 2026 | GATEWAY to Academic Articles

SAMESHIMA Naoto /
Department of Astronomy, Graduate School of Science, The University of Tokyo and
Department of Space Astronomy and Astrophysics, ISAS

Silicate minerals^*1 are the main constituents of rocky planets such as Earth. Therefore, investigating the properties of silicate minerals in protoplanetary disks, where planets form, is important for understanding the history of planet formation.
In this study, we observed protoplanetary disks using the James Webb Space Telescope (JWST)^*2 and compared the results with previous observations obtained by the Spitzer Space Telescope (SST)^*3. We found significant changes in the silicate features seen in mid-infrared radiation, suggesting that the disk structure may vary on timescales of several years.
In particular, both observations with the SST and JWST suggest that crystalline silicates are more abundant in cooler regions than amorphous silicates, namely in the outer parts of the disk. This indicates that crystalline silicates formed in the hot inner regions of the disk may have been transported outward. In the future, PRIMA^*4, NASA’s next-generation far-infrared mission in which Japan is also considering participation, may enable the detection of crystalline silicate features in cooler disk regions across many protoplanetary disks. This is expected to lead to a more statistical understanding of the temporal changes and spatial distribution of silicate minerals suggested by this study.

Research Summary

How did planets like the Earth, where we live, come into being? To approach this question, we need to observe newborn stars that are much younger than the Sun. Recent infrared and radio observations have revealed that young stars are surrounded by disk-like structures composed of gas and dust. These structures are called protoplanetary disks and are thought to be the birthplaces of planets. In particular, rocky planets like the Earth contain silicate minerals as one of their main building materials. Therefore, understanding what kinds of minerals make up the dust in protoplanetary disks, and how that dust changes over time, provides important clues to the process of planet formation.

In this study, we observed disks around the young stars Sz 96 and IP Tau, located in the star-forming regions of Lupus and Taurus, respectively. Using the JWST, we compared the mid-infrared silicate features (peaks and dips in radiation at particular infrared wavelengths that indicate the presence of silicates absorbing and emitting those wavelengths of light) with previous observations obtained by the SST. As a result, we found that the mid-infrared spectra (the plot of these features) observed with SST and JWST had changed overall (Figure 1). In this study, we analyzed this spectral change by focusing on the emission components from silicate minerals, and showed that the temperature, abundance, and crystallinity of minerals in the disk surface may have changed. This suggests that the disk structure may vary on timescales of several years. We also found that, in both objects, crystalline silicates have lower temperatures than amorphous silicates. At first glance, this is a surprising result, because crystalline silicates are thought to form when dust is heated in high-temperature environments, such as the inner regions of disks. Our results suggest that crystalline dust formed in such hot inner regions was later transported outward to cooler regions of the disk (Fig. 2). In other words, material within the disk may be actively moving and being redistributed.

This picture, in which crystals formed at high temperatures are found in low-temperature regions, has previously been suggested by observations with the Spitzer Space Telescope. In this study, however, the high wavelength resolution of JWST allowed us to identify spectral features characteristic of crystalline silicates more clearly than ever before. As a result, we were able to detect the presence of crystalline dust, and the difference in temperature between crystalline and amorphous dust, in a more robust way. These findings provide important clues showing that dust in protoplanetary disks is not simply present, but is formed in the inner disk, transported outward, and altered depending on its surrounding environment. This is an important result for understanding how the dust that eventually becomes the building material of planets evolves within disks.

Terminologies

• ^*1 Silicate materials: A general term for minerals composed mainly of silicon and oxygen. They are major components of rocks and sand on Earth and are among the basic building materials of rocky planets.
• ^*2 James Webb Space Telescope (JWST): An infrared space telescope operated by NASA in collaboration with ESA and CSA. It was launched on 25 December 2021.
• ^*3 Spitzer Space Telescope (SST): An infrared space telescope operated by NASA. It was launched on 25 August 2003 and ended its operations on 30 January 2020. Before JWST, it was one of the major space telescopes supporting infrared astronomy.
• ^*4 PRIMA mission: A next-generation far-infrared space telescope mission under consideration by NASA. It aims to study the formation and evolution of stars, planetary systems, galaxies, and cosmic dust through observations from the mid-infrared to far-infrared wavelengths.

Information

Links

• Article: JWST–DECO: temporal variations in the mid-IR silicate features of two T Tauri discs based on Spitzer and JWST observations

Author

SAMESHIMA Naoto
March 2025: B.S., Department of Astronomy, Faculty of Science, The University of Tokyo
April 2025-Present: Master’s Program, Department of Astronomy, Graduate School of Science, The University of Tokyo
April 2025-Present: Tsujimoto Laboratory, Institute of Space and Astronautical Science