An eerie nightglow on the planet Venus has appeared at
least twice to a European spacecraft, though a human would need infrared eyes
to spot it.
Previously-reported glows have revealed the chemical
breakdown of Venus' atmosphere. But this latest sighting represents a newly
discovered nightglow caused by nitric oxide in the planet's atmosphere, and has
proven useful for observing Venus' atmosphere.
"The nightglow can give us a lot of information,"
said Antonio Garcia Munoz, a former researcher at Australian National
University who has since relocated to the Instituto de Astrofísica de Canarias
in Spain. "It can provide details about the temperature, wind direction,
composition and chemistry of an atmosphere."
Europe's Venus
Express spotted the nightglow with its Visible and Infrared Thermal Imaging
Spectrometer (VIRTIS) instrument to record the nitric oxide levels on the
planet below. On Earth, the molecule can be found as a pollutant from cigarette
smoke, car emissions and power plants
The phenomenon speaks to the ongoing violence of the
sun's ultraviolet light pummeling
the planetary atmosphere, which breaks up molecules into simpler molecules
and atoms. Chemical fragments may recombine into molecules such as nitric
oxide, and give off energy in the form of light during the recombination phase.
Sunlight normally outshines
any faint glow on the day side of Venus. But the dark side provides ample
opportunity for Venus Express to catch an infrared show. Nitric oxide has also
made a showing
on Earth and Mars in the shorter
ultraviolet range, as opposed to infrared.
Previous Venus nightglows from oxygen and hydroxyl
molecules have been detected from 56 to 62 miles (90-100 km) up in the planet's
atmosphere. Nitric oxide light emissions have appeared slightly higher at the
68 to 75 mile (110-120 km) range.
"Luckily for us, Venus has a temperamental
atmosphere," Munoz said. "Packets of oxygen and nitrogen atoms are
blown around."
He explained that the whirling collection of atoms
sometimes became dense enough to boost the brightness of nightglow and make it
visible to VIRTIS. Venus Express can even pick up on all three types of
nightglows simultaneously.
However, when and why each of the three nightglows
appears remains a mystery for
now. Full results on this research appear in the January issue of the
journal Proceedings of the National Academy of Science.
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