An extremely high-altitude plume seen at Mars’ morning terminator

In the abstract they say there are 2 theories of the plume's source:

1) CO2 or H2O ice particulate reflecting solar radiation. They don't state where the particulate is coming from, but they claim the plume is likely cyclic in nature.

2) strong auroral emissions 1000x the brightness of earth's aurora. Caused by a strong magnetic anomaly.