Presenter: Shotaro SAKAI
Abstract:
Present Mars has a thin atmosphere and little water on the surface. Space missions have provided some evidences for the existence of liquid water and a thick atmosphere on ancient Mars. These evidences suggest Mars has experienced significant atmospheric loss up to the present. The magnetization of a planet significantly changes the nature of atmospheric escape, and the question of whether a planetary field shields atmosphere from erosion by the solar wind or not remains open. Ion escape processes from Mars are investigated under two hypothetical conditions, namely, no intrinsic magnetic field and weak intrinsic dipole field cases under present solar wind conditions based on multi-species magnetohydrodynamics simulations. The existence of a weak dipole field results in an enhancement of the tailward flux of planetary ions through the four escape channels. Two channels are associated with the open fields at the poles, and the others are caused by magnetic reconnection between the planetary and solar wind magnetic fields at the flank magnetopause. The ion escape rate with the weak dipole is greater than in the no-dipole case. The enhancement is significant for O2+ and CO2+, suggesting ion escape from the low-altitude ionosphere.