Vast spiral of ultraviolet light over Mars' South Pole

https://www.spaceweather.com/

SPIRAL LIGHTS ON MARS: NASA's MAVEN spacecraft has discovered something unexpected on Mars–and researchers are struggling to explain it.

"There is a vast spiral of ultraviolet light over Mars' South Pole," says Nick Schneider of the University of Colorado's Laboratory for Atmospheric and Space Physics. "We understand the origin of the light, but its shape is a mystery."

The light is "nightglow." We have it here on Earth, too, where it's called "airglow." During the day, ultraviolet radiation from the sun breaks apart compounds in the upper atmosphere. At night, the atoms reassemble, glowing as they put themselves back together again. On Earth, airglow looks like the aurora borealis; people can actually see it. On Mars, the emission is ultraviolet, invisible to the human eye.

MAVEN has been monitoring Martian nightglow for years, yet the spiral pattern was only recently recognized. Schneider recalls the 'Eureka moment': "We were preparing a demo on our lab's internal projection sphere (like Science on a Sphere), which turned out to be the first time we had plotted the UV glow in polar coordinates. The spiral 'popped' and we were all quite giddy."

The spiral is just the tip of the iceberg; the whole planet is surrounded by pulsating patterns of nightglow. High above the North Pole of Mars there is a luminous blob that pulses exactly twice a day. And around the equator there are three more blobs, evenly spaced, pulsing three times a day. Only the South Pole has a spiral, and it pulses once a day.

"It's pretty complicated," says Schneider.