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Astronomers map the “dark chemistry” of outer space

In the formation of potentially habitable planets, ices are a vital ingredient since they are the main source of several critical elements, such as carbon, hydrogen, oxygen, nitrogen, and sulfur (referred collectively as “CHONS”). These basic elements are important ingredients in both planetary atmospheres and molecules such as alcohols, sugars, or simple amino acids.

Now, using the James Webb Space Telescope (JWST), an international team of astronomers has obtained for the first time an in-depth inventory of the deepest and coldest ices in a molecular cloud. Besides simple ices like water, the experts identified frozen forms of a variety of molecules, ranging from carbonyl sulfide, ammonia, and methane to the simplest organic molecule methanol. To date, this is the most comprehensive mapping of the icy ingredients available to create future generations of planets and stars, before they are heated during the emergence of young stars.

“Our results provide insights into the initial, dark chemistry stage of the formation of ice on the interstellar dust grains that will grow into the centimeter-sized pebbles from which planets form in disks,” said study lead author Melissa McClure, an astronomer at the Leiden Observatory in the Netherlands. “These observations open a new window on the formation pathways for the simple and complex molecules that are needed to make the building blocks of life.”

The scientists also found evidence for more complex molecules and, although they did not yet manage to definitely attribute these signals to specific molecules, this is a major step toward the identification of complex molecules present in the icy depths of molecular clouds before stars are born.

“Our identification of complex organic molecules, like methanol and potentially ethanol, also suggests that the many star and planetary systems developing in this particular cloud will inherit molecules in a fairly advanced chemical state,” explained study co-author Will Rocha, another  astronomer at Leiden. “This could mean that the presence of precursors to prebiotic molecules in planetary systems is a common result of star formation, rather than a unique feature of our own solar system.”

Moreover, by detecting the sulfur-bearing ice carbonyl sulfide, the experts were able to estimate for the first time the amount of sulfur embedded in icy pre-stellar dust grains. As in the case of the other CHONS elements, this amount is less than the total amount expected to be present in the examined cloud, based on its density. Future research is needed to understand where these elements are hiding. 

“The fact that we haven’t seen all of the CHONS that we expect may indicate that they are locked up in more rocky or sooty materials that we cannot measure,” McClure explained. “This could allow a greater diversity in the bulk composition of terrestrial planets.”

“This is just the first in a series of spectral snapshots that we will obtain to see how the ices evolve from their initial synthesis to the comet-forming regions of protoplanetary disks. This will tell us which mixture of ices – and therefore which elements – can eventually be delivered to the surfaces of terrestrial exoplanets or incorporated into the atmospheres of giant gas or ice planets,” she concluded.

The study is published in the journal Nature Astronomy.

By Andrei Ionescu, Staff Writer

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