Venus atmosphere said curiously cold

A European spacecraft has discovered a surprisingly cold region high in the atmosphere of Venus, usually thought of as blisteringly hot, astronomers said.

The Venus Express orbiting spacecraft has uncovered a very chilly layer at temperatures of around minus 273 degrees Fahrenheit in the atmosphere 75 miles above the planet's surface, the European Space Agency reported from its Paris headquarters Monday.

That may be cold enough for the planet's thick, carbon dioxide atmosphere to freeze out as ice or snow, researchers said.

Despite Venus being much closer to the Sun than the Earth, the curious cold layer is much chillier than any part of the Earth's atmosphere, they said.

The cold layer exists along the planet's terminator, the dividing line between the day and night sides of Venus.

"The temperature profiles on the hot day side and cool night side at altitudes above 120 km [75 miles] are extremely different, so at the terminator we are in a regime of transition with effects coming from both sides," lead study author Arnaud Mahieux of the Belgian Institute for Space Aeronomy said.

The cold layer at the terminator is sandwiched between two comparatively warmer layers, researchers said.

"The finding is very new and we still need to think about and understand what the implications will be," Hakan Svedhem, ESA's Venus Express project scientist, said.

"But it is special, as we do not see a similar temperature profile along the terminator in the atmospheres of Earth or Mars, which have different chemical compositions and temperature conditions."