Numerical Estimation of X-ray Emission from Europa and Dependence on Solar Activity

Abstract

Tenuous Europa is now known as an X-ray emitter. X-ray emission from a tenuous planetary object has an intricate connection to its surface composition. By taking into account the solar X-rays incident on its surface as the source of excitation of X-rays from the surface, models of probable surface composition, and physical processes leading to the generation of X-rays from the surface, we developed a numerical model to understand its X-ray emission. The model computes the solar X-ray flux at Europa distance during representative cases of a solar cycle (0.01–100 MK). Energetic photon-induced events leading to the emission of X-rays from the surface results from photoelectric absorption and scattering. Taking into account five representative phases of a solar cycle and four probable models of surface composition, we estimated the X-ray energy flux generated from the satellite and as observed by the Chandra X-ray Observatory (CXO). During the representative quiet to flare cases, the X-ray flux available at Europa for surface energetics vary from 4.63 × 10⁻⁸ to 3.23 × 10⁻⁴ erg cm⁻² s⁻¹ (4.96 AU). Detectable X-ray energy flux from Europa at CXO varies from 5.27 × 10⁻²² to 9.44 × 10⁻²⁰ erg cm⁻² s⁻¹. We also observed that the least energy flux is always emitted from the water-ice model of the surface composition. The presence of impurities in water-ice is seen as enhancing the X-ray emission from its veneer.