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Sky Pulse in Ultraviolet

Vast Areas of Mars’ Night Sky Pulse in Ultraviolet

Using new data from the Imaging Ultraviolet Spectrograph (IUVS) on NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft, scientists have found that the atmosphere of Mars pulses in ultraviolet three times per night, and only during Martian spring and fall. The IUVS data have also revealed unexpected waves and spirals over the winter poles, while also confirming previous results from ESA’s Mars Express spacecraft that this nightglow was brightest over the winter polar regions. The brightenings occur where vertical winds carry gases down to regions of higher density, speeding up the chemical reactions that create nitric oxide and power the ultraviolet glow.

This image shows the ultraviolet nightglow in the Martian atmosphere. Green and white false colors represent the intensity of ultraviolet light, with white being the brightest. The nightglow was measured at about 70 km altitude by the Imaging UltraViolet Spectrograph instrument on NASA’s MAVEN spacecraft. A simulated view of the Mars globe is added digitally for context. The image shows an intense brightening in Mars’ nightside atmosphere. The brightenings occur regularly after sunset on Martian evenings during fall and winter seasons, and fade by midnight. The brightening is caused by increased downwards winds which enhance the chemical reaction creating nitric oxide which causes the glow. Image credit: NASA / MAVEN / NASA’s Goddard Space Flight Center / CU / LASP.

This image shows the ultraviolet nightglow in the Martian atmosphere. Green and white false colors represent the intensity of ultraviolet light, with white being the brightest. The nightglow was measured at about 70 km altitude by the Imaging UltraViolet Spectrograph instrument on NASA’s MAVEN spacecraft. A simulated view of the Mars globe is added digitally for context. The image shows an intense brightening in Mars’ nightside atmosphere. The brightenings occur regularly after sunset on Martian evenings during fall and winter seasons, and fade by midnight. The brightening is caused by increased downwards winds which enhance the chemical reaction creating nitric oxide which causes the glow. Image credit: NASA / MAVEN / NASA’s Goddard Space Flight Center / CU / LASP.

MAVEN wasn’t the first spacecraft to spot the nightglow on Mars. That honor belongs to ESA’s Mars Express mission, which entered orbit around the Red Planet in 2003.

But MAVEN was the first to capture the nightglow for what it is — a dynamic and constantly evolving phenomenon.

“It wasn’t until MAVEN came along in 2014 that we could actually snap this full picture five times a day as the planet rotates,” said Dr. Nick Schneider, a researcher in the Laboratory for Atmospheric and Space Physics at the University of Colorado and lead author of the study published in the Journal of Geophysical Research: Space Physics.

 

In the study, Dr. Schneider and colleagues used MAVEN’s IUVS instrument to snap images of Mars from a distance of 5,955 km (3,700 miles).

Those far-flung recordings allowed the team to trace the path of nightglow as it moved across the entire planet.

“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,” Dr. Schneider said.

“The ultraviolet glow comes mostly from an altitude of about 70 km (43.5 miles), with the brightest spot about 1,000 km (621 miles) across, and is as bright in the ultraviolet as Earth’s northern lights,” added Dr. Zac Milby, also from the Laboratory for Atmospheric and Space Physics at the University of Colorado.

“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 km/h (about 180 mph).”

The diagram explains the cause of Mars’ glowing nightside atmosphere. On Mars’ dayside, molecules are torn apart by energetic solar photons. Global circulation patterns carry the atomic fragments to the nightside, where downward winds increase the reaction rate for the atoms to reform molecules. The downwards winds occur near the poles at some seasons and in the equatorial regions at others. The new molecules hold extra energy which they emit as ultraviolet light. Image credit: NASA / MAVEN / NASA’s Goddard Space Flight Center / CU / LASP.

The diagram explains the cause of Mars’ glowing nightside atmosphere. On Mars’ dayside, molecules are torn apart by energetic solar photons. Global circulation patterns carry the atomic fragments to the nightside, where downward winds increase the reaction rate for the atoms to reform molecules. The downwards winds occur near the poles at some seasons and in the equatorial regions at others. The new molecules hold extra energy which they emit as ultraviolet light. Image credit: NASA / MAVEN / NASA’s Goddard Space Flight Center / CU / LASP.

The pulsations observed by the team reveal the importance of planet-encircling waves in the Mars atmosphere.

The number of waves and their speed indicates that the Martian middle atmosphere is influenced by the daily pattern of solar heating and disturbances from the topography of the planet’s huge volcanic mountains.

These pulsating spots are the clearest evidence that the middle atmosphere waves match those known to dominate the layers above and below.

“MAVEN’s main discoveries of atmosphere loss and climate change show the importance of these vast circulation patterns that transport atmospheric gases around the globe and from the surface to the edge of space,” said Dr. Sonal Jain, also from the Laboratory for Atmospheric and Space Physics at the University of Colorado.

Next, the authors plan to look at nightglow ‘sideways,’ instead of down from above, using data taken by IUVS looking just above the edge of the planet. This new perspective will be used to understand the vertical winds and seasonal changes even more accurately.

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N.M. Schneider et al. Imaging of Martian Circulation Patterns and Atmospheric Tides Through MAVEN/IUVS Nightglow Observations. Journal of Geophysical Research: Space Physics, published online August 5, 2020; doi: 10.1029/2019JA027318

This article is based on press-releases provided by the National Aeronautics and Space Administration and the University of Colorado.

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