Without the shielding by a strong intrinsic magnetic field like Earth, the Martian atmosphere is exposed to the solar wind. The Mars-solar wind interaction accelerates and transports planetary ions away from Mars through a number of processes, including pick-up by the electromagnetic field in the solar wind. The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft arrived at Mars in September 2014. Equipped with instruments to measure the solar wind, magnetic field, Extreme Ultraviolet (EUV) radiations, and planetary ions, MAVEN has provided further understandings of the planetary ion escape from Mars, and the dependence on solar wind, interplanetary magnetic field (IMF), and solar radiation conditions.
Based on the ion velocity and spatial distributions from MAVEN data, we have identified different ion populations near Mars, and first confirmed the existence of a substantial plume-like structure of energetic escaping ions in the upstream electric field direction, which constitutes an important ion escape channel in addition to the tailward escape. With the data taken from an over-one-year time span, we have also investigated the ion escape variations with upstream conditions, and found that different ion populations show different seasonal solar EUV variabilities. I will present our analysis of MAVEN data on the ion escape channels, loss rates, and seasonal variabilities.