Webb reveals the dark side of prestellar ice chemistry

An international team of astronomers using NASA’s James Webb Space Telescope announces the discovery of diverse ice in the darkest regions of a cold molecular cloud yet measured. The finding allows astronomers to examine simple, icy particles that will be incorporated into future exoplanets, while opening a new window on the origin of more complex particles that are the first step in creating the building blocks of life.

If you want to build a habitable planet, ice is a vital ingredient because it is the main source of several key elements – namely carbon, hydrogen, oxygen, nitrogen and sulfur (here referred to as CHONS). These items are important components of both planetary atmospheres and molecules such as sugars, alcohols, and simple amino acids.

An international team of astronomers using NASA’s James Webb Space Telescope has obtained an in-depth inventory of the deepest, coldest ice yet measured in a molecular cloud. In addition to simple ice like water, the team was able to identify frozen forms of a wide range of molecules, from carbonyl sulfide, ammonia and methane, to the simplest complex organic molecule, methanol. (Researchers considered organic molecules It is complex when there are six or more atoms present.)

This is the most comprehensive census yet of the icy ingredients available to make future generations of stars and planets, before they are heated up during the formation of young stars.

said Melissa McClure, an astronomer at the Leiden Observatory in the Netherlands, who is the principal investigator for the observation program and lead author of the paper describing the finding.

These notes open a new window on morphology paths for simplex and complex molecules needed to make the building blocks of life.”

In addition to the molecules they identified, the team found evidence of molecules more complex than methanol, and although they haven’t definitively attributed these signals to specific molecules, this proves for the first time that complex molecules form in the icy depths of molecular clouds before stars are even born. .

added Will Rocha, an astronomer at the Leiden Observatory who contributed to the discovery.

“This may mean that the presence of precursor molecules for prebiotics in planetary systems They are a common consequence of star formation, and are not a unique feature of our solar system. ”

by detecting sulfur-bearing ice carbonyl sulfideFor the first time, researchers have been able to estimate the amount of sulfur present in prestellar icy dust grains. While the measured amount is larger than previously observed, it is still less than the total amount that would be expected to be present in this cloud, based on its density.

This is true of other CHONS as well. The main challenge for astronomers is understanding where these elements are hiding: in ice, soot-like material, or rocks. The amount of CHONS in each type of material determines how much of these elements ends up in the outer planets’ atmospheres and how much in the interior.

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

The chemical properties of the ice were accomplished by studying how starlight from behind the molecular cloud is absorbed by the icy particles within the cloud at specific infrared wavelengths visible to Webb.

This process leaves behind chemical fingerprints known as absorption lines that can be compared with laboratory data to identify the ice in the molecular cloud. In this study, the team targeted ice buried in an extremely cold, dense and difficult-to-probe region of the Chamaeleon I molecular cloud, a region about 500 light-years from Earth that is currently in the process of forming dozens of young nuclei. stars.

“We simply could not have observed these ices without Webb,” said Klaus Pontopidan, Webb’s project scientist at the Space Telescope Science Institute in Baltimore, Maryland, who was involved in this research. “The ices appear as a dip against a continuum of background starlight. In regions that are very cold and dense, much of the light from the background star is blocked, and Webb’s remarkable sensitivity was necessary to detect starlight and thus identify the ices in the molecular cloud.”

This research forms part of the Ice Age Project, one of Webb’s 13 Science Early Release programs. These observations are designed to showcase Webb’s observing capabilities and to allow the astronomical community to learn how to get the best out of its instruments. The Ice Age team has already planned more observations, and hopes to trace the ice’s journey from its formation to the gathering of icy comets.

“This is just the first in a series of spectral snapshots we will get to see how ices evolve from their primitive composition to comet-forming regions of protoplanetary disks,” McClure concluded. “This will tell us which mixture of ices – and therefore which elements – could eventually be delivered to the surfaces of terrestrial exoplanets or incorporated into the atmospheres of gas giants or icy planets.”

These results have been published in natural astronomy.