Abiogenesis on Different Star Types; a Dissipative Photochemical Perspective

TL;DR

This paper tests the Thermodynamic Dissipation Theory for the origin of life (TDTOL) by evaluating how different main-sequence star types influence the surface UV-C/UV-B photon environment of Earth-like planets at their habitable distances. It models a six-step photochemical production sequence for UV-C pigments, using rate equations that couple production (αP) and degradation (βD) to a hydrolytic/chemical decay rate (k), and it analyzes how stellar spectral outputs shape stationary concentrations and buildup times. The results indicate that F, G, and high-mass K-type stars are most favorable for sustaining substantial prebiotic pigment formation and rapid progression toward biosynthetic complexity, while O/B offer excessive ionizing flux, and M-dwarfs pose severe challenges due to low precursor production, high flare activity, and tidal locking constraints. The study proposes a practical biosignature based on planetary soft UV-C albedo and photon-dissipation rates, guiding observational strategies to focus on stars most likely to host carbon-based life and highlighting the thermodynamic function of life as a target for detection.

Abstract

The thermodynamic dissipation theory for the origin of life asserts a thermodynamic imperative for the origin of life, suggesting that the fundamental molecules of life originated as self-organized molecular photon dissipative structures (chromophores or pigments) that proliferated over the ocean surface to absorb and dissipate into heat the Archean solar soft UV-C (205-285 nm) and UV-B light ($<$320 nm) of our G-type star. Shorter wavelength hard UV-C light ($<$205 nm) may, depending on atmospheric conditions, have reached Earth's surface and ionized and dissociated or otherwise degraded these carbon-based pigment molecules (as probably occurred on Mars after losing most of its atmosphere). Here we assess the possibility for an abiogenesis of life similar to ours through molecular photon dissipative structuring on planets similar to early Earth but orbiting different star types at distances normalized to the solar constant. Emission spectra of star types are analyzed to determine the ratio of integrated photon fluxes in the soft UV-C wavelength (dissipative structuring) to hard UV-C wavelength (degradation) regions. Our analysis suggests that star types favorable to the dissipative structuring of life, potentially evolving towards complex life forms such as bacteria, are only the F, G and high mass K-types, with intelligent life only possible on G-type stars. Low mass K and M-type stars are highly unlikely to harbor life. Biosignatures related to the thermodynamic imperative of photon dissipation are proposed.

Figures (13)

• Figure S1: The spectrum of UV light available at Earth's surface before the origin of life at approximately 3.9 Ga and until at least 2.9 Ga (curves black and red, respectively). This spectrum in the UV-C may even have persisted throughout the entire Archean until 2.5 Ga MeixnerovaEtAl2021. Atmospheric CO$_2$, H$_2$O, SO$_2$ and probably some H$_2$S, were responsible for the absorption of wavelengths shorter than $\sim$205 nm, and atmospheric aldehydes (e.g., formaldehyde and acetaldehyde, common photochemical products of CO$_2$ and water) absorbed between about 285 and 305 nm Sagan1973MellerMoortgat2000), approximately corresponding to the UV-B region (280 and 315 nm). By around 2.2 Ga (green curve), UV-C light at Earth's surface was completely extinguished by the pigments of oxygen and ozone resulting from organisms performing oxygenic photosynthesis. The yellow curve corresponds to the present surface spectrum. Energy fluxes are for the Sun at the zenith. Over 50 of the fundamental molecules of life are plotted at their wavelengths of maximum absorption: nucleic acids (black), amino acids (green), fatty acids (violet), sugars (brown), vitamins, co-enzymes, and cofactors (blue), and pigments (red). We have asserted that these molecules were dissipatively structured as UV-C pigments under this light. The font size is roughly proportional to the relative size of the respective molar extinction coefficient of the pigment. Adapted with permission from Michaelian and Simeonov MichaelianSimeonov2015.
• Figure S2: Conjugated carbon molecules are more stable (lower Gibb's free energy in the ground state) as compared to saturated molecules, but more importantly provide new collective electron orbitals giving rise to excited states at energies adequate for the absorption of soft UV-C photons. The greater the conjugation number, the greater the wavelength of maximum absorption. The wavelength of maximum absorption of the chromophore can, therefore, be tuned simply by a protonation or deprotonation event. Conjugation is also important for giving molecules a conical intersection (Fig. \ref{['fig:ConicalInt']}) allowing rapid dissipation of the electronic excited state energy into heat (internal conversion). Photon dissipation is the thermodynamic reason for the occurrence of organic molecules in nature. Reprinted with permission from Michaelian Michaelian2017
• Figure S3: A conical Intersection (CI) for excited adenine showing a degeneracy of the electronic excited state with the vibrational states superimposed on the electronic ground state after a UV-C photon absorption event (blue arrow) which induces a nuclear coordinate deformation from the molecules original planer structure in the Franck-Condon (FC) region to activation of an N9--H stretch or a ring-puckering motion known as pyramidalization (shown in the diagram). The most probable deformation depends on the incident photon energy and protonation state. It is this deformation, resulting from excitation of an anti-bonding state (e.g., $\pi \rightarrow \pi^*$), which leads to a lowering of the excited potential energy surface such that it intersects with vibrational states of the electronic ground state, resulting in the conical intersection. Conical intersections provide rapid (sub-picosecond) dissipation of the electronic excitation energy into vibrational energy (heat). The quantum efficiency, $q$, for this dissipative route is very large (> 99%) for many of the fundamental molecules of life, making them photochemically stable and, more importantly (from our thermodynamic perspective), very efficient at UV-C photon dissipation. Another common form of coordinate transformation mediated through conical intersections are proton and electron transfers within the molecule or with the solvent environment and this may have relevance to enzyme-less photon-induced denaturing of RNA and DNA MichaelianSantillan2019 and to photosynthesis MichaelianSimeonov2025. The diagram is based on data from Andrew Orr-Ewing Orr-Ewing, Roberts et al. RobertsEtAl2014, Kleinermanns et al. KleinermannsEtAl2013, and Barbatti et al. BarbattiEtAl2010). Reprinted with permission from Michaelian Michaelian2021.
• Figure S4: The photochemical dissipative structuring of adenine from 5 molecules of hydrogen cyanide (HCN) in water, first observed by Ferris and Orgel (1966) FerrisOrgel1966BoulangerEtAl2013. Four molecules of HCN (1) are transformed into the smallest stable oligomer (tetramer) of HCN, known as cis-2,3-diaminomaleonitrile (cis-DAMN) (2), which, under a constant UV-C photon flux, isomerizes into trans-DAMN (3) (also known as diaminofumaronitrile, DAFN) which can be converted, on absorbing two more UV-C photons, into an imidazole intermediate, 4-amino-1H-imidazole-5-carbonitrile (AICN) (7). Hot ground state thermal reactions with another HCN molecule or its hydrolysis product formamide (or ammonium formate) leads to the purine adenine (8). This is a microscopic dissipative structuring process which ends in adenine Michaelian2017Michaelian2021, a UV-C pigment with a large molar extinction coefficient at the maximum intensity of the UV-C Archean surface solar spectrum (260 nm - Figs. \ref{['fig:Pigments']}) and a peaked conical intersection facilitating rapid dissipation of photons at these wavelengths. The other nucleobases have similar optical characteristics and also appear to be UV-C molecular dissipative structures (e.g., reference HernandezMichaelian2022 and figure \ref{['fig:DNA-Abs']}). Reprinted with permission from Michaelian Michaelian2021.
• Figure S5: Absorption spectrum of 25bp DNA (including all DNA nucleobases) in the soft UV-C region showing hyperchromism resulting from the denaturing with temperature. The lower curves are the thermal difference spectra (right y-axis) obtained by subtracting the lower temperature extinction curve from the higher temperature curve for a 3 $^\circ$C bin centered at the specified temperature (smoothed with a 2000 point Bezier function). Peak absorption at $\sim$260 nm corresponds to the peak in the incident UV-C spectrum arriving at Earth's surface during the Archean (Fig. \ref{['fig:Pigments']}). Large broadband absorption implies rapid (sub-picosecond) dissipation of the electronic excitation energy into heat through conical intersections (Fig. \ref{['fig:ConicalInt']}). Reprinted with permission from Michaelian and Santillan MichaelianSantillan2019.