Mars in ultraviolet light is a wondrous place. By night, the dark side of the planet is aglow with nitric oxide. By day, clouds quickly merge together into banks that stretch 1,000 miles long.
The new view of Mars comes from the orbiting MAVEN spacecraft, which this month begins a third year of studies about how the planet most like Earth in the solar system lost most of its atmosphere.
When the spacecraft reaches the most distant part its orbit - MAVEN travels as far as 3,900 miles from Mars - its global view of the planet is giving scientists new insights, and in some cases first looks, at global wind circulation, ozone distribution and cloud formation.
The data about the winds comes from MAVEN images of "nightglow," a common phenomenon in which an atmosphere shines at night, despite the complete absence of illumination, MAVEN scientist Nicholas Schneider, with the University of Colorado, Boulder, told reporters at the American Astronomical Society meeting in Pasadena, Calif., this week.
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"Nightglow is the result of chemical reactions in an atmosphere," Schneider said. "In the case of Mars, the molecules are broken apart on the day side of the planet ... and those atoms are carried by the winds to the night side, primarily the winter pole, where they then descend to higher density and recombine. In that act of re-combining, they have enough energy to give off ultraviolet photons."
The nightglow molecules are nitric oxide and how they apparently spread over Mars means that computer models of the planet's flowing winds are in need of an upgrade.
The new data indicates that the winds around the planet, already subject to strong seasonal changes, are more irregular than expected, Schneider said.
That, in turn, raises questions about the transport of atmospheric molecules, and especially the chemistry that happens as a result, he said.
MAVEN's UV view of Mars also confirms theories that what little ozone Mars has is concentrated in the dry, polar regions where there is little water vapor to break up the molecules.
"The nature of the polar vortex and how long the ozone lasts through Spring provides insight into the evolution of ozone and water vapor, a coupled chemistry in the Mars atmosphere," Schneider said.
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Perhaps the most striking new look at Mars is time-lapse imagery of clouds forming and moving across the planet.
Clouds provide a way to trace atmospheric flows, and they affect the planet's energy balance, depending on whether sunlight is absorbed or reflected back into space, Schneider said.
"They also tell us about the inventory of water vapor that would be available for forming clouds," he added.
The images show which regions of Mars are relatively thick with atmosphere, such as the low-lying Meridiani Planum, where Europe's Schiaparelli lander will attempt to touch down on Wednesday.
The atmosphere is thinnest above Mars' tallest volcanoes, including Olympus Mons, the largest known volcano in the solar system.
Scientists do not yet know if the rapid buildup of Mars' cloud banks, which grow to 1,000 miles in about seven hours, is unusually fast or not. The MAVEN ultraviolet imagery is the first opportunity they've had for a planet-wide look.
Images: Ultraviolet images, rendered in false color to optical wavelengths, from the Mars-orbiting MAVEN spacecraft show cloud formation, particularly around the planet's tall volcano. The tallest, Olympus Mons, appears as a prominent dark region 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 (white areas near center) merging to span up to a thousand miles by the end of the day. Credit: NASA/MAVEN/University of Colorado
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