Free Astronomy Magazine May-June 2023

17 MAY-JUNE 2023 ASTRO PUBLISHING ane, to the simplest complex or- ganic molecule, methanol. (The researchers considered organic mol- ecules to be complex when having six or more atoms.) This is the most comprehensive census to date of the icy ingredients available to make fu- ture generations of stars and plan- ets, before they are heated during the formation of young stars. “Our results provide insights into the initial, dark chemistry stage of the formation of ice on the interstel- lar dust grains that will grow into the centimeter-sized pebbles from which planets form in disks,” said Melissa McClure, an astronomer at Leiden Observatory in the Nether- lands, who is the principal investiga- tor of the observing program and lead author of the pper describing this result. “These observations open a new window on the formation pathways for the simple and com- plex molecules that are needed to make the building blocks of life.” In addition to the identified mole- cules, the team found evidence for molecules more complex than methanol, and, although they didn’t definitively attribute these signals to specific molecules, this proves for the first time that complex mole- cules form in the icy depths of mo- lecular clouds before stars are born. “Our identification of complex or- ganic 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,” added Will Rocha, an astronomer at Leiden Observatory who contributed to this discovery. “This could mean that the presence of precursors to prebiotic molecules in planetary sys- tems is a common result of star for- mation, rather than a unique feature of our own solar system.” By detecting the sulfur-bearing ice carbonyl sulfide, the researchers were able to estimate the amount of sulfur embedded in icy pre-stellar dust grains for the first time. While the amount measured is larger than previously observed, it is still less than the total amount expected to be present in this cloud, based on its density. This is true for the other CHONS elements as well. A key chal- lenge for astronomers is under- standing where these elements are hiding: in ices, soot-like materials, or rocks. The amount of CHONS in each type of material determines how much of these elements end up in exoplanet atmospheres and how much in their interiors. “The fact that we haven’t seen all of the CHONS that we expect may indi- cate that they are locked up in more rocky or sooty materials that we can- not measure,” explained McClure. “This could allow a greater diversity in the bulk composition of terrestrial planets.” Chemical characterization of the ices was accomplished by studying how starlight from beyond the mo- lecular cloud was absorbed by icy molecules within the cloud at spe- cific infrared wavelengths visible to Webb. This process leaves behind chemical fingerprints known as ab- sorption lines which can be com- pared with laboratory data to identify which ices are present in the molecular cloud. In this study, the team targeted ices buried in a partic- ularly cold, dense, and difficult-to-in- vestigate region of the Chamaeleon I molecular cloud, a region roughly 630 light-years from Earth which is currently in the process of forming dozens of young stars. “We simply couldn’t have observed these ices without Webb,” elabo- rated Klaus Pontoppidan, Webb project scientist at the Space Tele- scope Science Institute in Baltimore, Maryland, who was involved in this research. “The ices show up as dips against a continuum of background starlight. In regions that are this cold and dense, much of the light from the background star is blocked, and Webb’s exquisite sensitivity was nec- essary to detect the starlight and therefore identify the ices in the mo- lecular cloud.” This research forms part of the Ice Age project, one of Webb’s 13 Early Release Science programs. These ob- servations are designed to showcase Webb’s observing capabilities and to allow the astronomical community to learn how to get the best from its instruments. The Ice Age team has already planned further observa- tions, and hopes to trace out the journey of ices from their formation through to the assemblage of icy comets. “This is just the first in a series of spectral snapshots that we will ob- tain to see how the ices evolve from their initial synthesis to the comet- forming regions of protoplanetary disks,” concluded McClure. “This will tell us which mixture of ices — and therefore which elements — can eventually be delivered to the sur- faces of terrestrial exoplanets or in- corporated into the atmospheres of giant gas or ice planets.” T his image by NASA’s James Webb Space Telescope’s Near-Infrared Camera (NIRCam) features the central region of the Chamaeleon I dark molecular cloud, which resides 630 light years away. The cold, wispy cloud material (blue, center) is illuminated in the infrared by the glow of the young, outflowing pro- tostar Ced 110 IRS 4 (orange, upper left). The light from numerous background stars, seen as orange dots behind the cloud, can be used to detect ices in the cloud, which absorb the starlight passing through them. [Image: NASA, ESA, CSA. Science: Fengwu Sun (Steward Observatory), Zak Smith (The Open Univer- sity), IceAge ERS Team. Image processing: M. Zamani (ESA/Webb)] !