Theoretical limits of passive daytime radiative cooling in extraterrestrial environments: implications for space exploration.

Passive daytime radiative cooling (PDRC) enables sub-ambient cooling without external energy input, a feature that has attracted significant research attention. While most studies have focused on PDRC performance in terrestrial environments, extraterrestrial settings offer the potential for superior cooling due to the absence of convective heat transfer and atmospheric thermal radiation. To address this gap, we investigate the extreme optical properties and radiative cooling performance of PDRC materials in extraterrestrial settings, specifically paints and ceramics, known for their strong solar reflectance, high thermal emissivity, and ease of fabrication. This investigation is grounded in a comprehensive theoretical framework that incorporates Mie scattering, Monte Carlo simulations, effective medium theory, and the transfer matrix method for ultra-broadband spectral simulations from vacuum ultraviolet to far-infrared wavelengths, followed by energy balance analysis in extraterrestrial environments. We explore the influence of particle size, volume fraction, and thickness in paints and ceramics on cooling performance to elucidate the theoretical limit of extraterrestrial PDRC. This study broadens the scope of PDRC research and provides valuable insights into the application of PDRC materials for future deep-space exploration.