Charge-equilibration of Fe ions accelerated in a hot plasma

We examine the energy-dependent rates of charge-changing processes of energetic Fe ions in the hot plasma of the solar corona. For ionization of the Fe-ion projectile in collisions with ambient protons, three different methods of estimating the corresponding ionization cross sections are presented and compared. Proton-impact ionization is found to be significant irrespective of the particular method used. Differences in the proton-impact ionization cross sections' estimates are shown to have little effect in calculating highly nonequilibrium Fe charge states during acceleration, whereas equilibrium charge states are sensitive to such differences. A parametric study of the Fe charge-equilibration comprises (i) impact of the ambient plasma density, and (ii) the energy dependence impact of the acceleration rate upon the charge-energy profiles and upon the estimated values of the density x acceleration-time product. We emphasize potential importance of careful measurements of charge-energy profiles along with ion energy spectra for determining the energy dependence of ion acceleration time and the energy dependence of the leaky-box escape time

Charge-equilibration of Fe ions accelerated in a hot plasma

We examine the energy-dependent rates of charge-changing processes of energetic Fe ions in the hot plasma of the solar corona. For ionization of the Fe-ion projectile in collisions with ambient protons, three different methods of estimating the corresponding ionization cross sections are presented and compared. Proton-impact ionization is found to be significant irrespective of the particular method used. Differences in the proton-impact ionization cross sections' estimates are shown to have little effect in calculating highly nonequilibrium Fe charge states during acceleration, whereas equilibrium charge states are sensitive to such differences. A parametric study of the Fe charge-equilibration comprises (i) impact of the ambient plasma density, and (ii) the energy dependence impact of the acceleration rate upon the charge-energy profiles and upon the estimated values of the density $\times$ acceleration-time product. We emphasize potential importance of careful measurements of charge-energy profiles along with ion energy spectra for determining the energy dependence of ion acceleration time and the energy dependence of the leaky-box escape time

Alteration of the Carbon and Nitrogen Isotopic Composition in the Martian Surface Rocks Due to Cosmic Ray Exposure

C-13/C-12 and N-15/N-14 isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce C-13 and N-15 isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both C-13 and N-15 due to galactic cosmic rays (GCRs) exposure can vary within 1.5-6 atoms/cm3/s depending on rocks' depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5-10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the "light," potentially "biological" C-13/C-12 ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e.g., 100 million years), cosmogenic changes in N-15/N-14 ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (N-15/N-14). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed