In a new analysis based on five years of observations using The European Space Agency's Venus Express satellite, scientists have uncovered a very chilly layer at temperatures of around -175C in the atmosphere 125 km above the planet's surface that may be frigid enough for carbon dioxide to freeze out as ice or snow.
The curious cold layer is far frostier than any part of Earth's atmosphere, despite Venus being much closer to the Sun, the Daily Mail reported.
The discovery was made by watching as light from the Sun filtered through the atmosphere to reveal the concentration of carbon dioxide gas molecules at various altitudes along the terminator - the dividing line between the day and night sides of the planet.
Armed with information about the concentration of carbon dioxide and combined with data on atmospheric pressure at each height, scientists could then calculate the corresponding temperatures.
"Since the temperature at some heights dips below the freezing temperature of carbon dioxide, we suspect that carbon dioxide ice might form there," Arnaud Mahieux of the Belgian Institute for Space Aeronomy and lead author of the paper, said.
Clouds of small carbon dioxide ice or snow particles should be very reflective, perhaps leading to brighter than normal sunlight layers in the atmosphere.
"However, although Venus Express indeed occasionally observes very bright regions in the Venusian atmosphere that could be explained by ice, they could also be caused by other atmospheric disturbances, so we need to be cautious," Mahieux said.
The study also found that the cold layer at the terminator is sandwiched between two comparatively warmer layers.
"The temperature profiles on the hot dayside and cool night side at altitudes above 120 km are extremely different, so at the terminator we are in a regime of transition with effects coming from both sides," Mahieux said.
"The night side may be playing a greater role at one given altitude and the dayside might be playing a larger role at other altitudes," Mahieux added.
Similar temperature profiles along the terminator have been derived from other Venus Express datasets, including measurements taken during the transit of Venus earlier this year.
