Venus is sometimes called the Earth's twin because of its similar size and orbital distance from the Sun, but it's more like a backwards, inside-out Earth. Venus rotates on its axis in the opposite direction from the solar system's other planets, and it's hot — surface temperatures average around 890°F. But it looks like Venus isn't hot all over.
New data from the European Space Agency's Venus Express orbiter has found a cold layer in the planet's upper atmosphere.
The cold layer exists about 78 miles above the surface along the terminator, the line between the day and night sides of the planet. In this very specific region, temperatures drop sharply to around -283°F. This is much colder than any part of Earth's atmosphere and below the freezing point of carbon dioxide, which suggests to some ESA scientists that carbon dioxide ice, or dry ice, could form in this chilly atmospheric layer.
The Venus Express team found this cold spot on Venus by measuring sunlight filtering through the atmosphere. The varying concentration of carbon dioxide gas molecules at different altitudes along the terminator, as well as data on atmospheric pressure at each height, enabled mission scientists to calculate the temperatures at various layers.
What's really interesting is that the cold layer localized at the terminator is sandwiched between two comparatively warmer layers, and two very different temperature profiles on Venus's hot dayside and cooler night side. With different atmospheric environments converging on the terminator, there are potentially some very interesting things happening that we have yet to fully reveal.
Confirmation and more details on the cold layer will come after scientists examine the role of other atmospheric components like carbon monoxide, nitrogen, and oxygen, since these dominate Venus' atmosphere more and more the higher one goes. More study might also shed light on why we don't see similar effects on terminators of any other bodies in the solar system.