Radiation from Proxima Centauri Reaching Its Planet Proxima b

Recently, interest in the planet Proxima b has increased following indications that liquid water may be present there. The literature has reported measurement data for the radiation spectrum of the star Proxima Centauri as received by this planet, together with an estimate of an effective temperature (3050 K) of that radiation, obtained from the Stefan-Boltzmann law for blackbody surface emission. This approach relies on a heat-balance assumption and does not yield a physically meaningful temperature suitable for heat-transfer calculations. Moreover, the irregular shape of the measured spectrum shows that this radiation cannot be treated as originating from a blackbody surface. Therefore, in the present work, the temperature of this radiation (3255 K) was determined using Planck’s law, based on the monochromatic radiation intensities at individual wavelengths. It was also shown that the temperature obtained in this way is ambiguous, representing only the minimal possible value. A further novelty of this study is the introduction of the most recent elements of thermodynamic analysis, specifically, the determination of the exergy of the radiation in question (693 W/m²). The exergy-to-energy ratio for this radiation was found to be 0.893, in close agreement with the theoretical value of 0.9042. Furthermore, the energetic and exergetic emissivities of Proxima Centauri’s surface were determined to be 0.6415 and 0.2019, respectively.