Observations of ICMEs at Mars: past and present

Throughout the inner heliosphere, the evolution of the solar wind interaction is a critical topic for weakly magnetized planets. In particular, the solar wind interaction with a planetary atmosphere during a space weather event offers a glimpse at how terrestrial atmospheres may have evolved during an earlier and more active epoch of the sun. While some of the most detailed observations of planetary ion loss, magnetic topology and particle acceleration have occurred during solar cycle 24, it has been one of the quietest solar cycles in the last half-century. Furthermore, as solar cycle 24 continues to decline, the frequency of solar transient events such as Interplanetary Coronal Mass Ejections (ICMEs) is also predicted to decline. Mars Global Surveyor (MGS) was observing the upper atmosphere of Mars during much of solar cycle 23, including the infamous 'Halloween' ICME in October of 2003. We will present MGS observations of the Halloween ICME at Mars and extrapolate ACE solar wind observations to 1.5 AU. We will use the IMF and solar wind observations during the Halloween ICME as initial inputs into a magnetohydrodynamic (MHD) and test particle simulation in order to construct a global picture of ion precipitation, escape, and magnetic topology throughout the event. We will simulate different phases of the Halloween ICME (the sheath and ejecta) and present comparisons of the simulation results to MGS observations. We will also place the Halloween storm in the context of other ICME observations during solar cycle 24, namely those observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The extreme conditions during space weather events may have had a significant influence on the evolution of the Martian atmosphere and may also have implications for exoplanets interacting with the stellar winds of younger, more active stars.