LAUSR

Abstract During September 2017, the solar active region (AR) 12673 produced several flares and Coronal Mass Ejections (CMEs). On 10 September 2017, a stronger and wider CME was erupted from AR 12673, which was Mars–directed (max. vsw ​= ​~840 ​km ​s−1 near 1.5 au). This ICME caused a major space weather event at Mars on 12–13 September. We investigated the impact of this event on Martian topside ionosphere by using the observations made by Langmuir Probe and Waves (LPW) and Suprathermal and Thermal Ion Composition (STATIC) instruments on board Mars Atmosphere and Volatile EvolutioN (MAVEN). LPW observed the ionopause feature at lower altitudes during the event period. This topside ionospheric compression and depletion observed by LPW was associated with enhanced electron temperatures. STATIC observed significant energization of ionospheric heavy ions such as O+ and O 2 + to energies above 10 ​eV up to hundreds of eV below 300 ​km altitude. Intense solar wind (lighter ions such as H+) penetration to lower altitudes was also observed. The increased energies for heavy ions and increased spread in energy for the lighter species are found at lower altitudes such as ~300 ​km, suggesting that significant heating and acceleration process is acting even at these altitudes during severe solar events.