International team discovers diverse ices in cold molecular cloud, opening window on origin of life building blocks.
An international team of astronomers using NASA’s James Webb Space Telescope has made a groundbreaking discovery of diverse ices in the darkest regions of a cold molecular cloud to date. This result allows astronomers to examine the simple icy molecules that will be incorporated into future exoplanets, while opening a new window on the origin of more complex molecules that are the first step in the creation of the building blocks of life. 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. The discovery of these ices provides insights into the initial, dark chemistry stage of the formation of ice on the interstellar dust grains that will eventually form the centimeter-sized pebbles from which planets form in disks.
In addition to the identified molecules, the team found evidence for molecules more complex than methanol, suggesting that the presence of precursors to prebiotic molecules in planetary systems is a common result of star formation. The detection of sulfur-bearing ice carbonyl sulfide also allowed the researchers to estimate the amount of sulfur embedded in icy pre-stellar dust grains for the first time.
Chemical characterization of the ices was accomplished by studying how starlight from beyond the molecular cloud was absorbed by icy molecules within the cloud at specific infrared wavelengths visible to Webb. This process leaves behind chemical fingerprints known as absorption lines which can be compared with laboratory data to identify which ices are present in the molecular cloud.
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. They also provide a greater understanding of the bulk composition of terrestrial planets, as the amount of CHONS elements in each type of material determines how much of these elements end up in exoplanet atmospheres and how much in their interiors.
This research forms part of the Ice Age project, one of Webb’s 13 Early Release Science programs. The Ice Age team has already planned further observations, and hopes to trace out the journey of ices from their formation through to the assemblage of icy comets. 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. The findings of this research were published in the January 23 issue of Nature Astronomy.