Whether in interstellar gas clouds, protoplanetary disks or comet dust: there are also organic molecules in space. These include simple hydrocarbons and alcohols, but also sugars, amino acids and even DNA bases. According to the common assumption, such complex organic molecules and building blocks of life arise from reactions of simpler precursors on the dust and ice grains of cold molecular clouds – the birthplaces of new stars. Our solar system and our Earth may also have “inherited” some of their organic chemistry from these grains.
Methanol (CH₃OH) plays a key role in the cosmic synthesis of life’s building blocks. This simplest organic alcohol is considered the starting point for the reaction chains through which more complex molecules are formed on interstellar dust and ice. Methanol reacts with carbon, oxygen and hydrogen to form ever larger compounds. But how exactly these reactions take place and under what conditions has only been partially clarified.
Deuterium instead of hydrogen
That’s why astronomers working with Arnaud Belloche from the Max Planck Institute for Radio Astronomy in Bonn have now used the ALMA radio telescopes in Chile to search for a specific methanol variant in the environment of young stars: deuterized methanol. In such molecules, one or more hydrogen atoms are replaced by the heavier hydrogen isotope deuterium. In addition to the proton, this has a neutron in the atomic nucleus. According to current models, molecules with a high proportion of deuterium are formed primarily under very cold conditions.
Methanol with normal hydrogen atoms and with deuterium. — © Angèle Taillard/ University of Toulouse/ IRAP
“Deuteration allows us to trace the chemical evolution of molecules during the formation of stars and planets,” explains co-author Silvia Spezzano, from the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching. “This allows us to understand their chemistry and ultimately how molecular complexity is transferred from interstellar clouds to planetary systems.” For their study, the team recorded radio spectra of eleven young stars in the Perseus molecular cloud, which is around 1,000 light-years away.
Spectral lines reveal deuterated methanol
The astronomers actually found what they were looking for: in the spectrum of the protostar IRAS4A2, they discovered the spectral signature not only of methanol, but also of several structural and isotopic variants of this alcohol. These also included the spectral lines of fully deuterated methanol (CD₃OD) – methanol molecules in which all hydrogen atoms have been replaced by deuterium.
“This is the first confirmed detection of fully deuterated methanol CD3OD in space,” report Belloche and his colleagues. At the same time, the “heavy” methanol they discovered is also the first known quadruple-deuterated molecule in interstellar space. The intensity of the spectral lines also told the researchers how high the proportion of the different methanol variants is in the protostar IRAS4A2. They compared these with common models of chemical composition in the environment of growing stars.
Much more common than the models predict
The surprising result: The fully deuterated form of mthanol occurs around a hundred times more frequently around the protostar IRAS4A2 than theoretically predicted. Where this excess deuterium comes from cannot yet be explained using any of the available astrochemical models. “A key process that drives the formation of multiply deuterated methanol therefore appears to be missing in all of these models,” says Belloche.
These observations therefore provide valuable information about as yet undiscovered chemical processes.
“Here we are gaining completely new insights into the complex chemistry that occurs in the environment of the youngest protostars,” explains Jes Jørgensen from the Niels Bohr Institute at the University of Copenhagen. “The exciting question is how these chemical components could influence the conditions on planets and possibly the emergence of life there.”
Still many unidentified spectral signatures
But even with the spectral analyzes from the nursery of the protostar IRAS4A2, some questions still remain unanswered. Numerous as yet unidentified spectral lines appeared in the spectra. It is still unknown which molecules or molecule variants these come from. However, Belloche and his team suspect that at least some of them come from methanol molecules that are only partially deuterated. Some other indications of chemical processes discovered in the young stars of the Perseus cloud also remain a mystery.
“We are just beginning to unlock the potential of this data set,” says Jeong-Eun Lee of Seoul National University in South Korea. “As we expand our analyses, we expect to uncover completely new aspects of chemical evolution on the path to planet formation.” In addition to the specialist article by Belloche and his team, six other publications have been published on the results of this project.
Source: Arnaud Belloche (Max Planck Institute for Radio Astronomy, Bonn) et al., Astronomy & Astrophysics, 2026; doi: 10.1051/0004-6361/202659642