A method for automatically detecting fires on Earth's surface using a satellite system is provided. The method includes acquiring multi-spectral images of the Earth at different times, using a multi-spectral satellite sensor, each multi-spectral image being a collection of single-spectral images each associated with a respective wavelength (λ), and each single-spectral image being made up of pixels each indicative of a spectral radiance (Rλ) from a respective area of the Earth. The method also includes providing a model relating the spectral radiances (Rλ) of each pixel in multi-spectral images acquired at different times and physical quantities representing thermodynamic phenomena occurring on the Earth's surface, in the Earth's atmosphere, and related to the Earth and the Sun relative positions. The method further includes computing for each pixel, at a given time, at least the physical quantity in the model representing a possible fire on the Earth's surface.