Every night on Mars, when the sun sets and temperatures fall to minus 80 degrees Fahrenheit and below, an eerie phenomenon spreads across much of the planet’s sky: a soft glow created by chemical reactions occurring tens of miles above the surface.

An astronaut standing on Mars couldn’t see this “nightglow”—it shows up only as ultraviolet light. But it may one day help scientists to better predict the churn of Mars’ surprisingly complex atmosphere.

“If we’re going to send people to Mars, we better understand what’s going on in the atmosphere,” said Zachariah Milby, a professional research assistant at the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder.

In a study published today in the Journal of Geophysical Research: Space Physics, Milby and his colleagues set their sights on understanding the phenomenon. They drew on data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to map the planet’s nightglow in greater detail than ever before.

The team’s findings show how this light display ebbs and flows over Mars’ seasons. The group also discovered something unusual: an unexpectedly bright spot that appears in the planet’s atmosphere just above its equator.

Mars, in other words, still has a few surprises in store for scientists, said LASP’s Nick Schneider, lead author of the new study.

“The behavior of the Martian atmosphere is every bit as complicated and insightful as that of Earth’s atmosphere,” said Schneider, also a professor in the Department of Astrophysical and Planetary Sciences.

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