Martian sky seen 'pulsing in ultraviolet light' by Nasa spacecraft

This is an image of the ultraviolet "nightglow" in the Martian atmosphere. Green and white false colors represent the intensity of ultraviolet light, with white being the brightest (NASA/MAVEN/Goddard Space Flight Center/CU/LASP)

Vast parts of the Martian sky are glowing in ultraviolet light, a Nasa spacecraft has found.

The unexpected pulsing light – discovered by the Maven spacecraft – follows a regular pattern, becoming visible three times each night and during the planet's spring and autumn.

The new observations also showed that there are strange waves and spirals visible over Mars's poles.

The results can now be used to better understand how the atmosphere on Mars behaves.

"Maven's images offer our first global insights into atmospheric motions in Mars' middle atmosphere, a critical region where air currents carry gases between the lowest and highest layers," said Nick Schneider of the University of Colorado, the lead author on a new paper detailing the research, in a statement.

The brightenings happen when winds carry gas from higher up in the atmosphere lower to regions where it is more dense, which in turn speed sup chemical reactions that create nitric oxide and switch on the bright ultraviolet glow.

The glow cannot be seen with the human eye but can be seen as shining light when viewed with specialised instruments.

"The ultraviolet glow comes mostly from an altitude of about 70 kilometers (approximately 40 miles), with the brightest spot about a thousand kilometers (approximately 600 miles) across, and is as bright in the ultraviolet as Earth's northern lights," said Zac Milby, who also works at Colorado's Laboratory for Atmospheric and Space Physics.

"Unfortunately, the composition of Mars' atmosphere means that these bright spots emit no light at visible wavelengths that would allow them to be seen by future Mars astronauts. Too bad: the bright patches would intensify overhead every night after sunset, and drift across the sky at 300 kilometers per hour (about 180 miles per hour)."

The lights show how waves that encircle the entire planet are key to the atmosphere of Mars. They seem to indicate that the atmosphere of Mars is influenced by the daily pattern of heat from the sun as well as distrubances from below, in the form of Mars' huge volcanic mountains.

The pulses are evidence that the waves found in the middle atmosphere match those known to exist in the layer above and below, showing how patterns circulate gas right across the Martian world, from its surface to the edge of space.

Now researchers hope to get a side-on view of the planet, rather than looking down from above, giving an even better understanding fo the vertical winds and seasonal changes that decide the "nightglow".