It is possible to explain such observations in general if we consider MEX to be above a region that has accelerated electrons upwards, in which case heavy-ions could also be accelerated downwards. This may explain the appearance of the very low DEF of heavy-ions at ∼400eV. However, due to the finite gyro-radius effect it is also plausible that the general behaviour of the heavy-ions flowing away from Mars may not change, even when passing an acceleration region. The gyroradius of heavy-ions with energies around ∼10eV at the location of the accelerated electron signature is around 100 km, which is of a similar spatial scale to the horizontal size of a closed crustal magnetic field line at 400 km. Therefore, it is possible the heavy-ions do not remain in the acceleration region long enough to experience its effects.
heavy-ions
DEF
∼400eV.
eV
heavy-ions
energies
∼10eV
eV
heavy-ions
gyroradius
around 100 km
km
closed crustal magnetic field line
horizontal size
400 km
km