Mysterious warm layer discovered in Venus' atmosphere

Scientists have discovered a warm layer in Venus' atmosphere, the nature of which is still unknown.
The researchers made the discovery when compiling a temperature map of the upper atmosphere on the planet's night side based on the data collected by the Venus Express probe.
"We measured temperatures at altitudes of 90 to 140 kilometres," said Denis Belyaev of Moscow Institute of Physics and Technology (MIPT) and the Space Research Institute of the Russian Academy of Sciences.
"On the night side of the planet, temperatures normally fall with altitude, but we noticed a peak in the chart in the 90 to 100 kilometre range.

"Here, the atmosphere was 20-40 degrees warmer than we expected. We don't yet understand what causes the warming, but Venus' ozone layer is at this altitude. There may be a connection," Belyaev said.
Belyaev, along with his colleagues from MIPT and the Space Research Institute, and researchers from the French laboratory LATMOS, as well as from Belgium, Germany and the US analysed the data obtained by the SPICAV spectrometer on board Venus Express between June 2006 and February 2013.

The European mission Venus Express was launched from the Baikonur space center in 2005 using the Russian rocket Soyuz-FG. The unit was removed from service in February 2015, but scientists continue to analyse the data it obtained throughout its operation.

The SPICAV system (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus) consisted of two spectrometers, an infrared one and an ultraviolet one.
Atmospheric temperatures were taken in the UV channel using the stellar occultation method, wherein a spectrometer captures the light emitted by a star as it goes behind a planet.
The starlight radiates through the planet's atmosphere, whose characteristics can be retrieved based on the spectrum produced.
The scientists selected stars that shine brighter in ultraviolet, that is, from 118 to 320 nanometres, the working range of the spectrometer.
Each second within the few minutes that the star took to disappear behind the planet's horizon the spectrometer took a shot of its spectrum.

Then the scientists divided the "atmospheric" spectrum by the star's "clean" spectrum to determine the gas composition and density of the atmosphere at different altitudes, as well as temperatures.
From June 2006 to February 2013 they made 587 "shots" of the atmosphere, which covered almost the entire night hemisphere.
"In almost every session of these seven years we detected a layer at altitudes of 90-100 km that is 20-40 kelvins warmer than it should be," said Belyaev.
"The air temperatures at these altitudes are 220-240 kelvins, while they should be under 200," said Belyaev.