The Martian bow shock: Wave observations in the upstream region

Distinct electric field oscillations in the frequency range from 4 to 40 kHz are detected by the plasma wave system in the upstream region of the bow shock during the operation of the Phobos 2 spacecraft around Mars. The upstream electron foreshock boundary approximately coincides with the magnetic field line tangential to the bow shock surface. A polarization analysis shows clearly that the electric field vector of the waves is aligned with the local magnetic field. The features of these high-frequency oscillations appear to be very similar to those of the emissions seen near the electron plasma frequency in the electron foreshock regions upstream of the bow shocks of Venus and Earth.