Energetic neutral atoms at Mars 4. Imaging of planetary oxygen

摘要: [1] Photoionization of the Martian oxygen exosphere/corona results in production planetary ions. The newborn ions start moving on cycloid trajectories determined by electric and magnetic fields solar wind. can then charge exchange with neutral gases (H, H2, O) exosphere be converted to energetic atoms (ENAs). Using empirical model wind flow near Mars developed Kallio [1996], we calculate interaction region obtain global distribution solving kinetic equation source sink terms. turns out highly asymmetrical a factor 1000 excess ion column density hemisphere which interplanetary field points. majority within 2Rm planetocentric distances (Rm is radius) have energies below 6 keV because typical size system too small for acceleration higher energies. About 50% experience change-exchange process that produces ENAs. Making line sight integration distribution, ENA images vantage points noon-midnight meridian plane are obtained. morphology clearly reflects structure parent distribution. ENAs energy 600 eV. For these integral flux up 104 cm−2s−1eV−1. differential fluxes high reach 105 cm−2s−1sr−1eV−1 range 0.1–1.7 keV, easily detected modern instrumentation. Planetary imaging at therefore feasible. total observed single point depends amount may used instantaneous escaping planet.