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On the Energy Flux Reaching Planets during the Parent Star’s Evolutionary Track:The Earth‐Sun System

The total flux of energy emitted by a star is a basic source of almost all physical and chemical processes in the atmosphere and on the surface of a planet. On the other hand, the upper parts of atmosphere, ionosphere, and magnetosphere are influenced to a great extent by tiny energy fluxes contained in the stellar XUV radiation and wind that are mostly responsible for ionization and photodissociation of atmospheric constituents and their escape. The latter problem is essential for the eventual detection of planets around stars. This paper demonstrates quantitatively how the above energy fluxes vary during a star’s evolution. The results are presented for a solar‐type star and a planet located initially at a distance of 1 AU from the star, providing insight into the past and future of the Sun and Earth. Among other things, the adopted model predicts that the maximum values of the energy flux reaching the Earth during giant phases of the Sun are greater than the respective values observed at present (the quiet Sun) by about 5 orders of magnitude for the solar wind, 3 orders of magnitude for the total radiation, and 2 orders of magnitude for the XUV radiation. On the other hand, the latter increases enormously (about 6 orders of magnitude) during a brief period of the post–asymptotic giant stage and decreases fast when moving to and during the white dwarf phase.