PLASMA AND WAVES AROUND MARS

The Plasma Wave System (PWS) on board the Soviet Spacecraft Phobos 2 has performed electron density and, for the first time, electric field measurements in the environment of the planet Mars. Electron plasma oscillations are observed upstream of the bow shock and yield a solar wind density of the order of 2 cm-3; the shock foot and/or ion foreshock are detected on each orbit. The altitude of the bow shock in the noon sector fluctuates between 0.45 and 0.75 Mars radii (R(ms)) above the planetary surface. The downstream solar wind, in the planetosheath, is characterized by increased plasma density and broadband electrostatic noise. The planetopause is crossed at altitudes of the order of 0.28 R(ms). Electro-magnetic waves with frequencies below the local gyrofrequency, propagating in the whistler mode, are recorded within the planetosphere, where the electron plasma density reaches unexpectedly large values, of up to 700 cm-3 at an altitude of 0.25 R(ms). Intense electrostatic emissions generated by heavy planetary ions are observed upstream of the shock; these waves are linked with the erosion process of the Martian atmosphere by the solar wind.