Chemical ‘primordial soup’: The James Webb Telescope has for the first time mapped the icy building blocks of life in a dark molecular cloud – the interstellar medium where stars and planets form. The spectral data show the presence of key elements of all life building blocks, which are present as water, methane and nitrogen ice, but also as complex organic molecules. This proves that many molecules necessary for life are already present in such cold stellar cradles, as the astronomers report in “Nature Astronomy”.
Cold, dark molecular clouds are the cradles of the planets: These interstellar clouds of molecular gas and ice-covered dust contain the building blocks from which stars and protoplanetary disks form. The ice layer of the interstellar dust grains acts like a catalyst: In it, elements such as carbon, oxygen, hydrogen, nitrogen and sulfur react to form sometimes complex organic molecules – and thus form the first building blocks of life.
The cold, dark heart
However, it has not yet been possible to fully determine which and how many life building blocks are hidden in the dark molecular clouds. The problem: Optical telescopes are blocked by the dust, and infrared telescopes can hardly detect radiation and the corresponding spectra because of the extreme cold and the dust in the center of these clouds.
This is where the James Webb Telescope comes into play: With it, astronomers led by Melissa McClure from the University of Leiden have for the first time been able to examine the existence of these icy building blocks of life in a dark molecular cloud. The team targeted the Chameleon I molecular cloud, 630 light-years from Earth, where dozens of new stars are currently forming.
Chemical primordial soup of the planets
For their study, the astronomers analyzed the absorption lines left by the cloud’s molecules and elements in the faint light from background stars shining through the dust. “Because most of this light is blocked, it took the external sensitivity of the Webb telescope to capture this light and identify the spectral signatures of the ice,” explains co-author Klaus Pontoppidan of the Space Telescope Science Institute in Baltimore.
The result is the first inventory of the icy building blocks of life at the center of an interstellar molecular cloud. “Our results provide insight into the first, dark phase of the ice chemistry on the interstellar dust grains, from which the centimeter-sized planetary building blocks later grow,” says McClure. “The observations reveal the pathways for the formation of the simple and complex molecules that form the raw material for the basic building blocks of life.”
All the key elements of life
Specifically, the spectral data showed that the ice-covered dust at the center of Chameleon I contains large fractions of water ice as well as frozen carbon dioxide and carbon monoxide. The silicates in the dust can also be seen in the spectrum. There is also frozen ammonia (NH4), cyanate (OCN) and the sulfur compound carbonyl sulfide (OCS), as the astronomers report.
The astronomers have thus identified key elements of life in this molecular cloud: carbon, hydrogen, oxygen, nitrogen and sulphur, also known as CHONS, are the raw materials from which almost all biomolecules are made. “These elements are important components of prebiotic molecules such as simple amino acids – and thus explain the ingredients of life, so to speak,” co-author Maria Drozdovskaya from the University of Bern.
Abundant organic molecule
In addition, the researchers also detected organic carbon compounds in the cloud, including methane (CH)4), methanol (CH3OH), ethanol (CH3 CH2OH), acetone (CH3COCH3) and acetaldehyde (CH3CHO). “The identification of complex organic molecules such as methanol, and likely ethanol, suggests that the stars and planetary systems forming in this cloud will inherit relatively widespread chemicals,” says McClure’s colleague Will Rocha.
According to the researchers, this suggests that precursors of prebiotic molecules in space are not the exception, but rather the rule. “It appears to be a more common result of star formation and not a unique feature of our solar system,” says Rocha.
Mystery of the missing remainder
But the first spectral look at the center of a molecular cloud also raises questions. Because the amounts of molecules and elements identified from the spectra are far below the expected values and those predicted by models. “We see a maximum of 19 percent of the carbon, 13 percent of the nitrogen budget and 1 percent of the sulfur budget in this dense cloud,” McClure and her colleagues state.
The astronomers suspect that the missing rest of these elements are hidden under the layers of ice around the dust grains – trapped in the minerals or a layer of carbonaceous soot on the grain surface. The form in which the elements are present there cannot be precisely determined on the basis of the current data. However, the team has already planned further observations with the James Webb telescope as part of its “Ice Age” project.
“This is just the first in a series of spectral snapshots that we plan to take,” explains McClure. “They should show us how these ices develop from their original formation to the comet-forming regions of the protoplanetary disks. This will tell us what ice mixes and elements eventually end up on the surface of terrestrial planets and in the gas envelope of gas planets and ice giants.” (Nature Astronomy, 2023; doi: 10.1038/s41550-022-01875-w)
Source: Space Telescope Science Institute, University of Bern
, Webb telescope icy life building blocks – First inventory of the elements and molecules in an interstellar molecular cloud