Article Posted on : - Feb 26, 2009

This artist's impression shows Venus Express focussing on studying the peculiar atmosphere of Venus, with a precision never achieved before. ESA photo

PARIS (BNS): Equipped with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument, ESA's Venus Express spacecraft has observed an eerie glow in the night-time atmosphere of Venus. The infrared light coming from nitric oxide has revealed to the scientists that the atmosphere of Earth’s nearest neighbour is a temperamental place of high winds and turbulence.

Sadly, the glow on Venus cannot be seen with the naked eye because it occurs at the invisible wavelengths of infrared.

Scientists said that VIRTIS had made two unambiguous detections of the so-called nightglow for nitric oxide at Venus. This is the first time such infrared detections have been made of any planet and provide a new insight into the atmosphere of Venus.
Antonio Garcia Munoz, who was at the Australian National University while conducting the research, said that the nightglow could give a lot of information. “It can provide details about the temperature, wind direction, composition and chemistry of an atmosphere,” Munoz, who is currently with the Instituto de Astrofisica de Canarias, Tenerife, Spain, said.

The researchers said that the nightglow is ultimately caused by the Sun's ultraviolet light, which streams into a planet's atmosphere and breaks the molecules up into atoms and other simpler molecules. The free atoms may recombine again and, in specific cases, the resulting molecule is endowed with some extra energy that is subsequently lost in the form of light. On the day-side of the planet, any atoms that do find their way back together are outshone by the sunlight falling into the atmosphere, they said.

But on the night-side, where atoms are transported by a vigorous diurnal circulation, the glow can be seen with appropriate instruments, such as VIRTIS, the scientists noted.

“A nitric oxide nightglow in the infrared has never been observed in the atmospheres of Mars or Earth, although we know that the necessary nitric oxide molecules are present because they have been observed in ultraviolet,” the researchers said.

Explaining at length, the researchers said that the nightglow on Venus has been seen at infrared wavelengths before, betraying oxygen molecules and the hydroxyl radical, but this is the first detection of nitric oxide at those wavelengths. “It offers data about the atmosphere of Venus that lies above the cloud tops at around 70 km. The oxygen and hydroxyl emissions come from 90-100 km, whereas the nitric oxide comes from 110-120 km altitude,” they said.

Meanwhile, Munoz said that even VIRTIS could not see the nitric oxide nightglow all the time because it is often just too faint. “Luckily for us, Venus has a temperamental atmosphere. Packets of oxygen and nitrogen atoms are blown around. Sometimes these become dense enough to boost the brightness of the nightglow, making it visible to VIRTIS,” Munoz explained.

“Venus Express can observe the three nightglow emissions simultaneously, and this gives rise to a mystery. The nightglows from the different molecules do not necessarily happen together. Perhaps when we have more observations, we will understand the correlation between them,” says Munoz.

To unravel the mysteries, the VIRTIS team plans to continue monitoring Venus, building up a database of this fascinating phenomenon.