Observations and Impacts of the 10 September 2017 Solar Events at Mars: An Overview and Synthesis of the Initial Results

On 10 September 2017, some of the strongest solar activity occurred in association with active region 12673 (AR2673), including an X-class solar flare and a fast coronal mass ejection. Although AR2673 was not centrally facing Mars, the activity impacted the local space weather conditions at Mars. We give an overview of observations obtained from the Mars Atmosphere and Volatile EvolutioN, Mars Science Laboratory, and Mars Express missions. Numerical results from the Wang-Sheeley-Arge (WSA)-Enlil-cone model together with Earth/L1 and STEREO-A observations are also presented to provide some heliospheric context. We discuss the initial results on the space weather impacts at Mars, which include heating of the upper atmosphere by solar flare emissions, flare-related enhancements of ion and neutral densities, solar energetic particles impacting the atmosphere and surface, bright emissions of a diffuse (global) aurora, deeply penetrating interplanetary magnetic fields over the Martian dayside, and enhanced atmospheric escape rates. Plain Language Summary When an X8.2 class flare and a fast and wide coronal mass ejection (CME) erupted from active region 12673 (AR2673) on 10 September 2017, the space weather impact was widespread and observed at multiple locations including Earth, Mars, and STEREO-A. The collection of papers in this GRL volume focuses on the observations and impacts at Mars triggered by these solar eruptive events. The space weather effects at Mars were simultaneously observed by instruments across several Mars missions, including Mars Atmosphere and Volatile EvolutioN, Mars Science Laboratory, Mars Express, Mars Odyssey, and also Trace Gas Orbiter. These September events began with two large M-class flares and one X-class flare observed at Mars together with CME activity seen in the solar coronagraphs at Earth. High fluxes of solar energetic particles associated with the flare and CME eruption were also detected. In this introduction, we provide an overview of the solar and heliospheric observations of the 10 September 2017 solar activity to provide context for the initial results on the space weather impacts. We present our summary and synthesis in this article.