Evaporation of planetary atmospheres due to XUV illumination by quasars

Planetary atmospheres are subject to mass-loss through a variety of mechanisms including irradiation by XUV photons from their host star. Here, we explore the consequences of XUV irradiation by supermassive black holes, as they grow by the accretion of gas in galactic nuclei. Based on the mass distribution of stars in galactic bulges and discs and the luminosity history of individual black holes, we estimate the probability distribution function of XUV fluences as a function of galaxy halo mass, redshift, and stellar component. We find that about 50 per cent of all planets in the Universe may lose a mass of hydrogen of ∼2.5 × 10¹⁹ g (the total mass of the Martian atmosphere), 10 per cent may lose ∼5.1 × 10²¹ g (the total mass of Earth's atmosphere), and 0.2 per cent may lose ∼1.4 × 10²⁴g (the total mass of Earth's oceans). The fractions are appreciably higher in the spheroidal components of galaxies and depend strongly on galaxy mass, but only weakly on redshift.