London: A group of scientists has found 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 European mission Venus Express probe.
The team of Russian, European and American scientists also found yet another peculiarity of Venus' upper atmosphere: early in the morning it is warmer than in the evening while it should be the other way round.
Venus is a unique planet that rotates not in the direction of its movement along the circumsolar orbit but in the opposite direction because its rotation axis is tilted 177 degrees.
It rotates very slowly - a solar day on the planet lasts 116 days.
During the long night the upper atmosphere cools, so at night it should be warmer than in the morning.
"We measured temperatures at altitudes of 90 to 140 km," said Denis Belyaev from the Moscow Institute of Physics and Technology (MIPT) in a statement.
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 km range.
"Here, the atmosphere was 20-40 degrees warmer than we expected. We do not yet understand what causes the warming, but Venus' ozone layer is at this altitude. There may be a connection," Belyaev said.
The team also found that the atmospheric temperature is 20 degrees warmer in the morning than in the evening.
"This is probably due to the global circulation of the atmosphere. The transition of the sub-solar point to the anti-solar point takes place at altitudes of about 100 km. In this area on the night side, the air mass goes down to 70 km, which may lead to the adiabatic heating of the atmosphere," the authors said.
The researchers continue to study the data collected by Venus Express, hoping to learn new information about the planet.