“The discovery of organic compounds in the disk of matter surrounding a young star raises questions. Where did amino acids originate?
Aldehydes, carboxylic acids, alcohols, or sugars—space is rich in chemical compounds. Astronomers have discovered around two hundred molecules in the Milky Way over the past decades. Most of them are organic substances, i.e., compounds consisting primarily of carbon and hydrogen. Many are considered precursors to important biological compounds. Treasure troves of complex hydrocarbons containing at least one carbon atom are the cold molecular clouds in star-forming regions, as well as young stars in whose immediate vicinity planets are growing.
In the planetary disk of the protostar V883 Orionis in the constellation Orion, scientists from the Max Planck Institute for Astronomy in Heidelberg recently discovered numerous organic molecules, including two compounds from which sugars, amino acids, and nucleic bases can form—building blocks from which terrestrial organisms produce proteins and nucleic acids such as RNA and DNA. The researchers led by Abubakar Fadul interpret this discovery as evidence that numerous prebiotic molecules may have already formed throughout space, not just on comets or asteroids.
Numerous biomolecules have indeed already been detected in asteroids, meteorites, and comets. For example, the US space probe Stardust detected the simple amino acid glycine (C2H5NO2) while flying through the tail of comet Wild 2 in 2006. The European space probe Rosetta also detected glycine in the tail of 67P/Churyumov-Gerasimenko nine years ago, along with the two precursor substances methylamine (CH5N) and ethylamine (C2H7N).
Conclusive evidence of amino acids and other prebiotic compounds in interstellar space has so far been lacking.
One possible cause could be the extreme conditions in the molecular clouds in which young stars form. Previously formed molecules are destroyed before they can further evolve, and can grow into amino acids, it is assumed. These organic compounds would then form later in the planet-forming disks of protostars. This is how they eventually reached asteroids and comets. However, most molecular clouds and planet-forming disks around the known protoplanets are too cold to easily detect organic molecules. The chemical reactions that lead to the formation of complex organic compounds preferentially take place on the surface of icy dust particles. Extremely low temperatures prevail there, at which the vibrational and rotational states by which molecules can be identified are frozen. And the larger the hydrocarbons, the more difficult their detection is.
An exception is the young active star V883 Orionis, 1300 light-years away. Its planetary disk extends far into space. Strong radiation outbursts have heated the material around the protostar to such an extent that it is gaseous over large areas and can be easily detected and studied in the radio spectrum. Even water, which is usually found in the water orbits the star in frozen form in the cold outer regions of the disk, but exists as vapor near the star. This was demonstrated by observations by a group of astronomers two years ago. The discovery is considered evidence that water in gaseous form also exists in interstellar space.
In fact, the Heidelberg astronomers' team, which also includes researchers from various American universities, used the European Southern Observatory's ALMA telescope array, which is sensitive to the shortwave radio range, to detect the spectral signatures of a total of seventeen organic molecules in the protoplanetary disk of V883 Orionis. These include methanol, acetone, dimethyl ester, and various salts of hydrogen cyanide, as well as the dihydric alcohol ethylene glycol (C2H6O2) and glycolonitrile (C2H3NO). These two compounds are possible precursors of simple amino acids such as glycine and alanine, as well as the nucleic base adenine, a building block of RNA and DNA. The determined concentration of the two substances is higher than in known Star-forming regions and other protoplanetary disks, and only slightly less than in the comet tails of Hale-Bopp and 67P, as reported in the "Astrophysical Journal Letters."
However, the Max Planck researchers led by Abubakar Fadul do not believe that the detected organic molecules first formed in the protoplanetary disk of V883 Orionis. Rather, they originated from earlier phases, when the protostar formed in a cloud of molecules and dust. The chemical evolution of the compounds continues in the planetary disks. In fact, according to the researchers found the time between the energetic protostar phase and the formation of a stable protoplanetary disk too short for more complex molecules to form in detectable quantities.
"Our results suggest that there is a direct evolutionary chain between interstellar molecular clouds and fully formed planetary systems, with a constantly increasing chemical diversity and complexity," says study leader Abubakar Fadul.
Further evidence for this hypothesis comes from laboratory studies: "Ethylene glycol can be formed from ethanolamine by irradiation with UV light," says Tushar Suhasaria, co-author of the study and head of the MPI Laboratory for the Study of the Origins of Life at the University of Jena. Ethanolamine was first discovered in a molecular cloud in the center of the Milky Way a few years ago. "This finding suggests that ethylene glycol is formed not only in early star-forming regions, but also in later stages of development when UV radiation plays a dominant role."
However, the MPI researchers have not yet been able to decipher and classify all the spectral lines they found in their spectra. Fadul and his colleagues acknowledge that the finding is still subject to some uncertainty. However, detailed observational data across a wider range of the electromagnetic spectrum would confirm the detection of ethylene glycol and glycolonitrile. It may then be possible to identify even more complex compounds, says Fadul.
Dutch astrochemist Ewine van Dishoeck from the Leiden University Observatory, who was not involved in the measurements, is convinced by the high quality of the ALMA data and their analysis. She also considers the theory that complex molecules formed in the molecular clouds at a very early stage of star formation and are preserved in the planetary disk to be plausible. "This 'inheritance' of complex chemistry from molecular clouds to planet-forming disks to comets has already been suspected in other studies. To now also conclude this on the basis of more complex molecules is a nice confirmation," says van Dishoeck. The fact that biomolecules such as amino acids have not yet been found in interstellar space could, in her opinion, be due to the fact that their signatures are very weak and, even in the case of glycine, difficult to detect conclusively.
Even if pieces of the puzzle are already in place, there is still a long way to go before we can prove that the evolution of life actually begins in open space." [1]
1. Die Samen der Biomoleküle. Frankfurter Allgemeine Zeitung; Frankfurt. 30 July 2025: N2. Von Manfred Lindinger
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