An international team of astronomers using the James Webb Space Telescope has discovered a variety of molecules, from relatively simple ones like methane to complex compounds like acetic acid and ethanol, in early-stage protostars where planets have not yet formed. These are key ingredients for creating potentially habitable worlds.
Complex organic molecules in space
The presence of complex organic molecules (COMs) in the solid phase of protostars was first predicted decades ago based on laboratory experiments, and previous detections of these molecules have been made by other space telescopes. This includes the Webb Early Ice Age Discovery Program, which has detected a variety of ices in the darkest and coldest regions of the molecular cloud measured to date.
Now, thanks to the unprecedented spectral resolution and sensitivity of the Webb Mid-Infrared Instrument (MIRI) as part of the JOYS+ (James Webb Observations of Young Protostars) program, these COMs have been individually identified and confirmed as being present in interstellar ice. This includes the robust detection of acetaldehyde, ethanol (what we call alcohol), methyl formate, and probably acetic acid (the acid found in vinegar) in the solid phase.
“This discovery answers one of the long-standing questions of astrochemistry,” says team leader Will Rocha of Leiden University in the Netherlands. – “Where do COMs come from in space? Are they formed in the gas phase or in ice? The discovery of COMs in ices suggests that solid-phase chemical reactions on the surface of cold dust grains can create complex types of molecules.”
COMs in ice
Since some COMs, including those found in the solid phase in this study, were previously found in the warm gas phase, they are now believed to originate from sublimation of ice. Sublimation is the transition directly from a solid to a gas without being converted to a liquid. Therefore, the discovery of COMs in ice gives astronomers hope for a better understanding of the origin of other, even larger molecules in space.
Scientists are also trying to find out to what extent these COMs are transferred to planets at later stages of the protostar’s evolution. Compostable substances in ice are transferred to planetary disks more efficiently than gas from clouds. Therefore, these icy NEOs can be inherited by comets and asteroids, which in turn can collide with the forming planets. In such a scenario, COMs could be delivered to these planets, potentially providing the ingredients for life to flourish.
What the molecules tell us
The science team also discovered simpler molecules, including methane, formic acid, sulfur dioxide, and formaldehyde. Sulfur dioxide, in particular, allowed the team to investigate the sulfur budget available in protostars. In addition, it is of prebiotic interest, as existing research suggests that sulfur-containing compounds played an important role in metabolic reactions on primordial Earth.
Negative ions have also been identified. They are part of salts that are crucial for the development of further chemical complexity at higher temperatures. This indicates that ice can be much more complex and requires further research.
Of particular interest is that one of the sources under study, IRAS 2A, is characterized as a low-mass protostar. Therefore, IRAS 2A may have similarities with the initial stages of our solar system. If this is the case, the chemical species found in this protostar could have been present in the early stages of our solar system and later made their way to the primitive Earth.
Comet transportation
“All of these molecules could become part of comets and asteroids and eventually new planetary systems as icy material is transported into planet-forming disks as the protostellar system evolves,” van Dishoek said.
Scientists hope to trace this astrochemical footprint step by step with more Webb data in the coming years.
Another recent paper by Pooneh Nazari of the Leiden Observatory also raises astronomers’ hopes of discovering a more complex ice structure after the previous detection of methyl cyanide and ethyl cyanide using NIRSpec data.
Nazari said: “It’s impressive how Webb now allows us to investigate the chemical composition of ice down to the level of cyanide, an important ingredient in prebiotic chemistry.”
