Space radiation is one of the main factors affecting habitability. Galactic Cosmic Rays (GCRs) impacting a planetary/small body surface, directly and/or generating considerable particle showers in an eventual atmosphere, can break molecular bonds of molecules at the surface or in the subsurface. Solar Energetic Particles (SEPs), linked to transient events on stars, and the solar wind can have both a destructive effect on biomolecules or trigger their formation [1,2,3].
The study of the impact of high and moderate energy radiation such as GCRs and SEPs on planetary/small bodies is generally done via Monte Carlo particle transport methods, which allow a “condensed history approach” of the very particle track, considering water as proxies for biological matter [4,5]. This is almost justified as water represents the main constituent of life as we know it, and at the high energy of the directly impacting particles the details of any eventual biomolecule immersed in the water sample would not be determinant.
However, the effectiveness of such radiation in inducing biological damage is linked, to a remarkable extent, to the details of the energy deposition stage by the impact particle (and lower energies secondaries generated in water hydrolysis) into the target, and to the relationship between initial energy deposition and chemical evolution of the defects, and their eventual biological consequences/effects. At present, the effectiveness of such radiation in inducing biological damage in a realistic target composed by water+biomolecule is still subject to considerable uncertainties , a topic of relevance also for particle therapy and space medicine. The critical issue of understanding the details of such energy deposition is obviously also of importance for radiation that naturally impact biological molecules in an energy range that is, from the very start, lower than GCRs, such as the solar wind and SEPs.
In all these cases, for detailed investigations of the survival of fundamental chemical bonds for life, a condensed history approach of Monte Carlo particle transport tools is not sufficient anymore. A detailed tracking of the structure of the particles paths is needed and the entity of the molecule can play a role as the chemical elements/type of bonds/ and dimensions of the molecule can influence its resistance to radiation. Still, Monte Carlo track structure codes essentially work only with the physics given by impact cross sections on the sole water, there is no real consideration of the electronic/chemical characteristics of the hosted biomolecule . Limitations given by such an approach have been highlighted, but on the positive side a massive effort is being done to follow the different steps of radiation effects until the more macroscopic biological damage.
The study of the processing of planetary/small bodies by radiation in the context of the study of possible destruction mechanisms/rise of biomolecules must rely on approaches that are able to consider several types of targets and processes occurring in the intermediate/low energy region. Radiation physics is obviously fundamental for the formation of secondary molecules that can be generated at any astronomical environment. Thus, similarly to the case of recently developed photochemical databases of different organic molecules detected in different astronomical environment , efforts to obtain calculated quantities to build up future databases of radiation impact cross sections will be needed.
In this contribution we would like to highlight how a chain of models from different communities could be of help to define the stability under radiation of certain of biomolecules, in different scenarios. In particular, calculations of radiation impact cross sections on water and small biological units, nowadays possibly calculated via first principles approaches , can be given as input to Monte Carlo track structure codes, extending the capabilities of the latter to more realistic targets. The role of quantum chemistry/electronic structure is nowadays well established in the study of planetary atmospheres, interstellar medium, planetary interiors, photochemical escape and prebiotic chemistry . Given the physical limitations and high costs of irradiation experiments, quantum chemical calculations offer an efficient approach that can boost the understanding of radiation physics and also consolidate already existing MC track structure codes. Such calculations can support basic science and could, one day, help in making use of Monte Carlo track structure codes not only for space medicine/particle therapy but also for assessing the survival of organics/biomolecules on planetary/small bodies. We suggest that such calculations can fill critical knowledge gaps in the concept of habitability, by determining the survival of critical bonds for the biological units and their eventual polymerization to more interesting targets. We suggest that a robust interaction between the planetary/small bodies community and physical chemists/chemical physicists would be beneficial in the future to understand the limit of life around different type of stars.
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