Mars, in all its ultraviolet glory

It just celebrated a Martian year orbiting the red planet. Now, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has beamed back images of the ultraviolet glow of Mars’ atmosphere, unveiling details never before seen.

“MAVEN’s elliptical orbit is just right,” said Justin Deighan of the University of Colorado, Boulder, who led the observations. 

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“It rises high enough to take a global picture, but still orbits fast enough to get multiple views as Mars rotates over the course of a day.”

The false-colour images snapped by the spacecraft’s Imaging Ultraviolet Spectrograph show the dynamic nature of the Martian atmosphere. Vast clouds arise at the summit of volcanoes, blurring and merging as the day wears on.

Ozone levels shift during the seasons, getting a boost when water vapour freezes out of the atmosphere.

What’s more, the processes that take place on the planet’s nightside – that is, the side facing away from the sun – were also mapped, showing the irregular nature of the atmosphere’s high winds.

This nightglow is produced by nitric oxide emissions that glow in the ultraviolet. Atoms formed from the breakdown of carbon dioxide and nitrogen that started on the planet’s dayside, triggered by the sun’s ultraviolet light, are carried around to the dark side by winds whipping around the planet.

On the nightside, those winds dip to lower altitudes, dragging the atoms with them. There, oxygen and nitrogen atoms collide to form nitric oxide, and as they do so, they emit a tiny flash of ultraviolet light.

This phenomenon is seen on other planets in the solar system and planetary scientists predicted they’d also find it on Mars. MAVEN’s data confirm it.

On the dayside, Mars’ south pole is lit up with ultraviolet emissions. These come from ozone in the atmosphere. 

Ozone is destroyed when in the presence of water vapour, but in the southern hemisphere winter any water vapour in the polar atmosphere is frozen out and falls as snow.

MAVEN’s images show ozone lasting well into spring.

Cloud capping the tops of the planet’s massive volcanoes grow with the Martian day too, MAVEN showed. The process is similar to the way clouds form over mountain ranges on Earth.

The work was presented at the American Astronomical Society Division for Planetary Sciences meeting in Pasadena, California.