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Mars, in all its ultraviolet glory

New images snapped by NASA's MAVEN spacecraft highlight previously invisible features of the Martian atmosphere. Belinda Smith reports.

The series interleaves MAVEN images to show about seven hours of Mars rotation during this period, just over a quarter of Mars' day. They show how rapidly and extensively the clouds topping the volcanoes form in the afternoon. Similar processes occur on Earth, with the flow of winds over mountains creating clouds.
NASA / MAVEN / University of Colorado

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.

"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 image of the Mars nightside shows ultraviolet emission from nitric oxide (NO). The emission is shown in false colour with black as low values, green as medium and white as high. The splotches, streaks and other irregularities in the image are indications that atmospheric patterns are extremely variable on Mars' nightside.
NASA / MAVEN / University of Colorado

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.

A mosaic of images taken near the Martian South Pole. Darker regions show the planet's rocky surface and brighter regions are due to clouds, dust and haze. The white region centred on the pole is frozen carbon dioxide (dry ice) on the surface. Pockets of ice are left inside craters as the polar cap recedes in the spring, giving its edge a rough appearance. High concentrations of atmospheric ozone appear magenta and the wavy edge of the enhanced ozone region highlights wind patterns around the pole.
NASA / MAVEN / University of Colorado

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.

Rapid cloud formation on Mars. The ultraviolet colours are false-coloured. Mars’ tallest volcano, Olympus Mons, appears as a dark patch near the top of the image, with a small white cloud at the summit that grows during the day. Three more volcanoes appear in a diagonal row, with their cloud cover (yellowish areas near centre) merging to span up to 1,600 kilometres by the end of the day.
NASA / MAVEN / University of Colorado

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

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Belinda smith 2016 2.jpg?ixlib=rails 2.1
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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