Abstract EANA2025-160

The habitability of planets beyond the Solar System has long been a topic of fundamental importance for astrobiology. Photosynthesis, crucial in the evolution of terrestrial life and atmospheric composition, may operate differently under the spectral condition of M-dwarfs. The evaluation of its potential efficiency is essential to estimate exoplanets’ habitability. M-dwarfs consist of around 70% of all stars in the galaxy, and they represent promising candidates for hosting habitable planets. However, their unique spectral and thermal characteristics—such as lower surface temperatures (2,400–3,790 K), extended pre-main-sequence super-luminosity, intense flaring activity, and frequent coronal mass ejections-, could lead to atmospheric erosion or the loss of surface water on planets within the habitable zone (HZ). On Earth, the process of photosynthesis occurs between 400 – 700 nm, in the photosynthetically active radiation (PAR), with Chlorophyll a absorbing in the blue and red region of the visible spectrum. In contrast, M-dwarfs absorb between 700 – 900 nm, in near-infrared (NIR). Different research suggests that the photon surface flux on these stars would peak in the 0.93 -1.1 µm for the anoxygenic scenario, with underwater photosynthesis potentially extending to 1.1–1.4 µm bands. The analysis of TRAPPIST-1 and Proxima Centauri offers two interesting possibilities to investigate the potential photosynthetic scenario on two exoplanets within the HZ: TRAPPIST-1e and Proxima Centauri b. Atmospheric models that consider stellar flux scaling, planetary gravity, and luminosity, suggest that both exoplanets could sustain cloud layers and greenhouse gases. Analysis of the attenuation factor (AF), which quantifies its reduction through the atmosphere, reveal interesting absorption features. Proxima Centauri b exhibits irregularities in the 1.5 and 2.5 – 3.5 microns range, suggesting specific molecular absorption bands. TRAPPIST-1e shows periodic peak around 1.5 microns, corresponding to the presence of water vapor, methane or CO2. Peaks around 2-3 microns are usually associated to water vapor, an interesting aspect for the habitability. Pressure/temperature (P/T) profile highlights differences between the two planets. TRAPPIST-1e shows a broader temperature range and a bump at moderate pressure, suggesting possible heating mechanisms or radiative absorption processes. Proxima Centauri b P/T profile is more compressed with higher pressure (>10⁻¹ atm) near the surface. The extended stellar lifetimes of M-dwarfs may provide sufficient time for exoplanets in the HZ for biological evolution. Moreover, terrestrial analogue environments – such as microbial mats and hydrothermal vent system-, can be set as examples of photosynthesis that might adapt to similar conditions as M-dwarfs: it is necessary to embrace what we already know about planetary environments that may differ from us.