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tokens: the Milky Way GRB scenario, we take Band parameter values: E 0 = 187.5 keV, α = −0.8, β = −2.3, spread over 1 keV–10 MeV range (Thomas et al. 2005 ). We obtain 3.96 × 10 18 eV cm −2 deposited in the top 1 g cm −2 of the atmosphere. The spectral information for the interstellar cloud scenario was obtained from Cummings, Stone Steenberg ( 2002 ) following the method in Pavlov et al. ( 2005 , 2011 ) giving the total fluence of 8.8 × 10 11 eV cm −2 s −1 . For modelling extreme solar events, estimating the spectrum is difficult because most of the events occurred before the satellite age. We selected the spectrum of the 2005 January 20 event here, because even though the event was not large by any standards, it was very well studied by a number of groups using both satellite and ground-based measurements. We rescaled its total energy to the Carrington event (2 × 10 33 erg) and took the Martian distance into account. The energy deposition rate was found to be 3 × 10 11 eV cm −2 s −1 assuming the event was spread over 24 h. The ion pair generation energy w of CO 2 is 33 eV ion pair −1 . The primary mechanism at play is photochemical escape, for example: CO 2 → CO + e − CO + O → O + CO O + + CO 2 → O + CO etc. A complete description of all the reactions and associated energetics can be found in standard textbooks such as Schunk Nagy ( 2009 ). We divide the deposited energy obtained from simulations by the ion pair generation energy to calculate ion pairs for each scenario. Our results are spread over a wide range of ion production rates, 1.2 × 10 16 ion pairs cm −2 s −1 from a Galactic GRB to 2.8 × 10 7 ion pairs cm −2 s −1 from gamma rays of an SN at 100 pc. Fig. 3 shows the ion production rates of different events along with their durations. Particles can escape the Martian atmosphere with just 0.125 eV amu −1 energy. With charge exchange, the fast ion becomes neutral and escapes, and the slower ion gets trapped in the magnetic field. Fast ions can directly knock the atoms out of the atmosphere, this process is known as sputtering. Ions also escape by gaining energy from ambipolar diffusion and by thermal escape according to Jeans equation. A Galactic GRB would directly deposit energy, produce ions (1.2 × 10 16 ion pairs cm −2 s −1 ) and transfer energy to kinetic energy of ions. The event is short lived but the magnitude of ionization and energy transfer is large. Thermal expansion due to a large energy deposition is possible in this scenario. In the nearby SN case, the gamma-ray and cosmic ray enhancements are ∼1 and ∼100 yr long, respectively. In addition to ion escape by large energy transfer, a fraction of the ions will also be picked up by solar wind and ICMEs during the period. Encounter with dense interstellar clouds would result in a ∼1-Myr-long enhancement in ionization rates (∼10 10 ion pairs cm −2 s −1 ). Extreme solar events are short-lived but as seen in Fig. 3 , can do significant damage and are relatively more frequent. Figure 1.