Interesting. But given the lack of magnetic field, how does the particles enter the atmosphere on the backside (night side) of the planet? On Earth it's easier to understand due to the magnetic field and that the polar regions also are very close to the day-side at all times.

Mars does have a magnetic field, just not a global one like Earth does. It likely had a global magnetic field in the past.

Probably was soon after sunset.

Very cool. It's too bad that Chroma noise is apparently quite visible on other planets too.

It took me a while to understand what looks like a legend in the article's image. I don't think it is a legend, those are color swatches showing that if you subtract the aurora color from the left image and add it to the right, the resulting color is very similar ("Observed sky" on left is similar to "Observed sky + aurora" on right), strongly suggesting the presence of green aurora.