Juan Carlos del Valle Morales deals with dust and molecules in the interstellar medium. The interstellar medium is the matter and radiation found between the stars of a galaxy. It is much emptier than the best vacuum humans can create, though it contains a mixture of gas and small, solid dust particles made of silicates, iron or carbonaceous material, which may be covered by ices. The astrochemist is particularly interested in these dust grains.
According to a hypothesis by Chyba and Sagan (1992)1, life on Earth could have originated from molecules from space that were brought to Earth by numerous comet and asteroid impacts around 3.85 billion years ago. Molecules are able to react with each other in the interstellar medium, often on the surface of dust grains, giving rise to complex molecules and in some cases the building blocks of our life.
Juan Carlos del Valle Morales explains how this could have happened: “Reactions tend to make molecules bigger. Some events like radiation can give the molecule energy, making it dettach from the surface or even splitting it. Once they float freely in space, they may attach to another object, reacting further. Sometimes they are attracted or compacted into larger objects like metheorites that could end up landing on a planet like Earth. This is how life could have originated in our planet. There are successive processes after this delivery, but life on Earth does come in one or way or another from outter space.”
The (Z)-1,2-ethenediol molecule could have been involved in such an event. It consists of an organic compound that is considered a precursor for sugars such as ribose. Ribose, in turn, is a component of RNA. “One of the proofs that molecules already react in the interstellar medium are RNA aminobases, e.g. uracil, which has been detected on asteroids. So we have seen it with our own eyes,” explains Juan Carlos del Valle Morales.
In contrast, most of the data on the chemical composition of the interstellar medium comes mainly from observations with radio interferometers. These consist of many individual telescopes that can be used to see the signals from space. “They record the spectral features of astronomical objects, analyze them and compare them with experiments carried out on Earth. From that we can identify molecules, quantify their abundance and even deduct physical properties of the studied region,” says del Valle Morales. “We then try to construct how they were formed.“
HCO as the father of more complex molecules
In his doctoral project, the scientist has simulated how the molecule (Z)-1,2-ethenediol could have formed on the surface of dust grains under the extreme conditions of the interstellar medium. To this end, he is first investigating how the molecule HCO - the product of the reaction between carbon monoxide (CO) and hydrogen (H), could have formed. “We know that this molecule is the father of many of the complex organic molecules we have in space,” says del Valle Morales. HCO is one of the many sugar precursors, a very reactive radical that can form multiple molecules. Such processes could therefore explain how simple molecules in interstellar clouds become complex organic molecules.
The reactions in the interstellar medium can take place either in gas clouds or on dust grain surfaces. At temperatures as low as minus 270 degrees Celsius, the dust grains are encased in a layer of ice. “In this temperature range and in almost total vacuum, reactions still take place, albeit in a different way than on Earth,” explains Juan Carlos del Valle Morales. He is exploring the insights of the hydrogenation of carbon monoxide, a very simple molecule with only two components, abundant in the interstellar medium and found in form of ice.
Simulating the formation of HCO with machine learning
To simulate the behavior of the molecules, he uses approaches from data science: methods such as machine learning and atomistic neural networks. “We use these to try to find out what happens during hydrogenation. In our experiment on the computer, we reconstruct the crystalline CO structure and add the hydrogen. The HCO molecule was then formed in the simulation,” explains del Valle Morales. To do this, he needed a lot of data from quantum chemical calculations, such as energies and forces from smaller models. With the help of machine learning methods, it was possible to carry out a large number of calculations with this data, for example, with thousands of atoms. “This would be unthinkable with conventional quantum chemistry,” says the scientist.
Formation of HCO as an explanation for the formation of more complex biomolecules
Simulations are based on models that try to recreate reality as close as possible. CO ices can be crystalline, which was modeled as a hemisphere (there is a basic structural pattern repeated along space). The peculiarity about it is that the outer atoms (shown in blue) have fixed positions. They do not move during the simulation to prevent the structure from being destroyed.
Photo: (c) Juan Carlos del Valle Morales
This is the result of one hydrogenation on a CO ice. On Earth, hydrogen is usually present as H2, but in space the most abundant species is H (atomic). The hydrogen atom interacts with the CO surface to proceed with the reaction H + CO → HCO. In the picture, the HCO molecule is highlighted in blue. HCO is a very important radical species that participates in many reactions in the interstellar medium.
Photo: (c) Juan Carlos del Valle Morales
Hydrogenation can be performed multiple times (highlighted in blue) due to the flux of H in space, which has an impact on the surface model. Thus, multiple HCO molecules can be generated, as seen here. And there are further reactions that could happen such as HCO + H → H2CO (this will be part of future research and therefore cannot be revealed at this point).
Photo: (c) Juan Carlos del Valle Morales
Theoreticians can produce data that experimentalists can interpret. Here, the model of a crystalline CO ice was used and simulated at very low temperatures (5 to 20 degrees Kelvin or -268 to -253 degrees Celsius). The X-ray diffraction pattern was then plotted. The model (blue to green lines) reproduces the experimental reference (red lines) with very good agreement. This shows that the model reflects reality.
Photo: (c) Juan Carlos del Valle Morales
When simulating the formation of (Z)-1,2-ethenediol on ice surfaces, the scientists made another interesting observation regarding isomerism. Isomers are molecules with the same atoms but in different arrangements. This means that you can get different molecules with the same atoms. For example, one oxygen may be on the left side of a carbon double bond and the other on the right, or they might both be on the same side. Such molecules are similar, but not the same. “In this project, we were able to find out how they were formed. It has to do with the surface. Depending on how the molecule came to be on the surface of the grain, we obtain only one of the isomers, the other, or both simultaneously,” explains del Valle Morales.
Finding out what happens on the surface was one of the goals of his project. But there is still a lot of research to be done. Juan Carlos del Valle Morales explains. "The origin of life is an extremely complex problem. It likely involves molecules formed in space over millions of years and different conditions. Evolution is an on-going process. Just as an example, RNA molecules are thought to have performed at the same time the genetic and metabolic functions that nowadays are carried out by DNA and proteins, respectively. So the problem is much more complex than we think.”
1Chyba, C., Sagan, C. Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life. Nature 355, 125–132 (1992). https://doi.org/10.1038/355125a0
Read more
Del Valle, J. C., Redondo, P., Kästner, J., & Molpeceres, G. “Formation of the Interstellar Sugar Precursor, (Z)-1,2-Ethenediol, through Radical Reactions on Dust Grains.” Astrophys. J. 974, 129 (2024). http://dx.doi.org/10.3847/1538-4357/ad6f9a
About the scientist
Juan Carlos del Valle Morales comes from Spain and studied Theoretical Chemistry and Computational Modelling at the University of Valladolid. He received the "Extraordinary End of Career Award" from the University of Valladolid for his Master's thesis, in which he investigated the formation of the molecule (Z)-1,2-ethenediol in the gas phase. He is currently working on his PhD in Theoretical Chemistry with Prof. Dr. Johannes Kästner in the SimTech Project PN 3-4 (II) at the University of Stuttgart. In addition to Spanish, he speaks four other languages: Chinese, German, English, and French. His work in astrochemistry reminds him of how small and insignificant human beings are, and he sometimes finds it strange to work with such different scales, such as extremely small atoms on the one hand and millions of years on the other.