PICKED-UP PROTONS NEAR MARS - PHOBOS OBSERVATIONS

The measurements carried out by the plasma spectrometer, ASPERA, onboard the PHOBOS-2 spacecraft show that protons, originating in the extended hydrogen corona of Mars, were observed at altitudes less-than-or-equal-to 7500 km. The cyclotron instability of these pickup ions appears to generate Alfven waves observed by the MAGMA magnetometer. Analysis of the plasma data shows that weak pitch-angle diffusion of a ring-distribution of pickup protons occurs. The altitude profiles of pickup proton fluxes and number densities of the parent hydrogen atoms are derived.