Revisiting the Strongest Martian X-Ray Halo Observed by XMM-Newton on 2003 November 19–21

On 2003 November 20–21, when the most intense geomagnetic storm during solar cycle 23 was observed at Earth, XMM-Newton recorded the strongest Martian X-ray halo hitherto. The strongest Martian X-ray halo has been suggested to be caused by the unusual solar wind, but no direct evidence has been given in previous studies. Here, we examined the Mars Global Surveyor (MGS) observations and found unambiguous evidence of unusual solar wind impact during that XMM-Newton observation: the whole induced magnetosphere of Mars was highly compressed. By comparing the solar wind dynamic pressure estimated at Mars from MGS observation and that predicted by different solar wind propagation models, it is further supported that the interplanetary condition during the XMM-Newton observation is not related to the quiet solar wind, but to solar wind disturbances with enhanced dynamic pressure, which is probably related to the interplanetary coronal mass ejection observed at Earth on 2003 November 20. A solar energetic particle event also impacted Mars during the XMM-Newton observation and lasted for several days. Its impact on the production of the X-ray emission from Mars may be worth investigating in the future.