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Using the James Webb Space Telescope (JWST), astronomers from Johns Hopkins University (JHU) and elsewhere have detected water ice in a debris disk around HD 181327—a young star located within 160 light years away from the Earth. The finding was reported in a paper May 14 in the journal Nature.

Debris disks are collections of small bodies around stars, including asteroids, Kuiper belt objects, comets, and also micron-sized debris dust. Observations of debris disks could help us better understand the evolution of planetary systems, the composition of dust, comets, and planetesimals outside our solar system.

Given that water plays a key role in the formation of planets and minor bodies, astronomers look for its presence also in debris disks. However, although water ice has been commonly detected in Kuiper belt objects and comets in the solar system, no definitive evidence for water ice in extrasolar debris disks has been found to date.

Now, a recent study conducted by a team of astronomers led by JHU's Chen Xie claims the discovery of water ice in a debris disk of HD 181327—an F6-type star at a distance of some 155.5 light years away. The detection was made using JWST's Near-Infrared Spectrograph (NIRSpec).

"Here, we report the discovery of water ice in the HD 181327 disk using the James Webb Space Telescope Near-Infrared Spectrograph," the researchers write in the paper.

The disk of HD 181327 is at a distance of approximately 84 AU and its width is about 25 AU. Previous observations of this disk have identified the presence of volatile-rich planetesimals similar to comets and Kuiper belt objects. This, together with the star's relatively young age of 18.5 million years, makes the disk a young Kuiper belt analog and therefore an excellent place to search for water ice.

Xie's team reports that the disk reflectance spectrum of HD 181327 at 90–105 AU from it has a broad bowl-shaped dip between 2.7 and 3.4 µm. This is consistent with the 3 µm feature of water ice. Moreover, they detected a narrow and strong peak at 3.1 µm in both the disk spectrum and its reflectance spectrum and they attribute it to the Fresnel peak of water ice, as observed in the spectra of Saturn's rings and Kuiper belt objects.

"The presence of the Fresnel peak is indicative of refractive lensing by the crystalline form of large (i.e., >1 mm) water ice particles," the astronomers explain.

Therefore, based on the new findings, the scientists conclude that the debris disk of HD 181327 harbors a water-ice reservoir, rich in materials found in icy bodies in the outer parts of the solar system.

The water-ice mass fraction at the outer part of the disk around HD 181327 was measured to reach 13.9% and the disk was found to be dynamic, with micron-sized icy particles being continuously created and destroyed.

In addition to the detection of water ice, the study also found the presence of iron sulfide and olivine in the investigated disk. The authors of the paper explained that iron sulfide has been found in micrometeorite and comet samples, while olivine is a very common refractory dust species in protoplanetary disks, debris disks, as well as in comets and asteroids.

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