Mass composition of the Martian escaping flux
The existence of liquid water in an early stage of Mars has been suggested from geomorphologic features. The once thick and wet atmosphere became the thin and cold modern atmosphere that could not sustain flowing water anymore. Studying the atmosphere evolution between these two stages necessary turns the attention to how the atmosphere has been losing material through time; specifically how the hydrogen and oxygen has been removed from the planet's atmosphere.
A major portion of our understanding of the processes by which Mars is losing its atmosphere come from in-situ data obtained by the missions Phobos-2, Mars Global Surveyor, Mars Express and more recently MAVEN.
Using more than 6 years of ion measurements from the ASPERA-3/IMA analyser on-board the Mars Express mission, the mass composition of the three main outflowing heavy ion species: O2+, O+ and CO2+ is studied. The results show that molecular oxygen ions dominate part of the dayside area very close to the planet and the central tail region as well. On the other hand, atomic oxygen rules in the terminator area and above following a pattern aligned with the induced magnetospheric boundary.