Dependence of X-ray emission from Europa on solar activity cycle

BRIGHT, SMART KUNDASSERY; Babu, C A

Abstract

The atmosphere of the Jovian Europa being tenuous, the interaction of the energetic solar photons is a probable source of excitation for the emission of X-rays from the surface of the satellite. Solar photons in the X-region of the electromagnetic spectrum have energies greater than the binding energy of the elemental constituents of the surface, cause excitation of electrons, and on de-excitation cause emission of X-rays through X-ray fluorescence. We developed models for the computation of the solar X-ray flux during the representative phases of a solar activity cycle (1-100 Å), and using these fluxes, we computed the photon-induced X-ray fluorescent and Rayleigh scattering emission flux from the regolith of the
Europa by taking into account its predominant H2O ice composition. This work observed that during the extreme case of the quiet Sun condition and an X2-class flare, the X-ray energy flux at the Europa distance of 4.96 AU vary from 1.08 × 10-7 to 5.23 × 10-4 ergs-cm-2s-1. This flux from the H2O ice composition can generate a total X-ray energy flux, inclusive of the X-ray fluorescent and Rayleigh scattering events, varying as 1.40 × 10-23 to 6.21 × 10-20 ergs-cm-2s-1. These computed numbers of the X-ray energy fluxes at the telescope of the Chandra X-ray Observatory are of lesser magnitude in comparison to its observed numbers (3.0 × 10-16). This deduction reveals the influence of a stronger excitation source than the photon-induced mechanisms of the generation of X-rays from the surface of the Europa.

Keyword(s)

Solar corona; Europa; Tenuous; Exosphere; X-ray fluorescence; Rayleigh scattering

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