'Dangling OH' discovered within interstellar ice in deep space

Scientists are making discoveries in the cosmic realm, probing deep into the universe’s dense cloud cores and uncovering secrets of interstellar ice and “dangling OH” that were once unobservable.

And who’s to thank for these revelations? None other than the James Webb Space Telescope (JWST).

Interstellar ice and stars

The team, comprising researchers from Max Planck Institute for Extraterrestrial Physics (MPE), conducted a pioneering study in the Chamaeleon I region.

Here, they harnessed the power of JWST’s Near Infrared Camera (NIRCam) to measure spectroscopic lines toward hundreds of stars behind the cloud, a technique previously thwarted by high extinction within dense cloud cores.

The study, recently published, divulged a fascinating discovery — detection of ‘dangling OH’ spectroscopic features for the first time.

These features indicate that water molecules aren’t fully bound in the ice. They could trace the porosity and evolution of icy grains from molecular clouds to protoplanetary disks, offering significant insights into ice grain structure and its vital role in planet formation.

Thanks to the unprecedented sensitivity of the JWST, we are able to probe ices deep within dense cloud cores, where extinction is so high that they eluded previous observatories.

Making sense of the spectroscopic lines

The probing of dense cloud cores in the Chamaeleon I region, a close section of the Milky Way, revealed starlight interacting with icy grains before being collected by JWST’s large mirror.

Until now, scientists had only observed major, intense absorption features tied to significant species in the ice, including water, carbon dioxide, carbon monoxide, methanol, and ammonia.

However, the new JWST era, armed with the telescope’s large mirror, allows the measurement of much weaker features.

Detailed examinations of these weak spectroscopic features provide insights into the physical conditions of the object.

One such breakthrough has been the first-ever detection of a particular set of very weak bands linked to a small fraction of the water molecules in the ice.

Decoding ‘dangling OH’

This ‘dangling OH’ feature, named by laboratory astrophysicists, corresponds to unbound water molecules within the ice.

These features could trace surfaces and interfaces within the icy grains or denote the intimate mix of water with other molecular species in the interstellar ice.

Interestingly, these ‘dangling OH’ features had been actively searched for since the 1990s, but space observatories lacked the required spectral resolution and sensitivity.

It was hoped that their detection could be used to trace the porosity of the ices. Their presence could signal fluffy grains with high porosity, while their absence could indicate compaction and aggregation.

“The detection of the water dangling bond feature in the ice mantles demonstrates the importance of laboratory astrophysics to interpret JWST data,” says Barbara Michela Giuliano, one of the authors of the study.

Giuliano further emphasized the need for extensive lab support to disentangle the spectral properties observed within dense regions of the interstellar medium and protoplanetary disks.

“The high sensitivity of JWST, together with impressive advancements in laboratory astrophysics, is finally allowing us to study in detail the physical structure and chemical composition of interstellar ices,” noted Paola Caselli, who also contributed to the paper. “It is exciting to be part of this endeavor.”

Interstellar ice, dangling OH, and planets

The study confirmed the presence of potentially ‘fluffy’ icy grains in the cloud, characterized by their porous and loosely bound structure, which significantly impacts the chemistry and degree of chemical complexity that can build up in these regions.

This discovery not only alters our understanding of the microphysical properties of interstellar ice but also offers a fresh perspective on planet formation.

By revealing the intricate processes that govern the spatial distribution and evolution of ices, researchers can now better comprehend how these ices transition from molecular clouds to protoplanetary disks and ultimately integrate into forming planets.

This enhanced understanding is crucial for developing more accurate models of planetary system formation and the potential for habitability on newly formed planets.

The full study was published in the journal Nature Astronomy.

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