A study conducted by McGill University, Canada, has discovered that the temperatures on the nightsides of planets similar to Jupiter in other solar systems are surprisingly uniform. This research also suggests that the dark sides of these planets have clouds made of minerals and rocks.
Data collected by the Spitzer Space and the Hubble Space telescopes suggests that the nightside temperature of 12 Jupiter-like planets, or hot Jupiters, was around 800°C.
Unlike the Jupiter in our solar system, hot Jupiters orbit their stars in very small circles. By having such a small orbital field, it only takes these hot Jupiters less than three days to complete its orbit. This also means that these planets do not rotate as the Earth does, however, it is more similar to our moon in that it always has a dark side.
Although one side is perpetually hot from facing its star, the dark side is not perpetually cool. Scientists have noticed a significant amount on the dark side of these hot Jupiters with some indication of heat transfer.
Dylan Keating, a Physics PhD student under the supervision of McGill professor Nicolas Cowan, said: “Atmospheric circulation models predicted that the nightside temperatures should vary much more than they do…This is surprising because the planets we studied all receive different amounts of irradiation from their host stars and the dayside temperatures among them varies by almost 1700°C.”
“The uniformity of the nightside temperatures suggests that clouds on this side of the planets are likely similar to one another in composition. Our analysis suggests that these clouds are likely made of minerals such as manganese sulfide or silicates: in other words, rocks,” Keating explained.
Due to the universal basic physics of cloud formations, the study of the nightside clouds on hot Jupiters could give an insight into other cloud formations. Other space missions could still further categorise the dominant cloud composition on hot Jupiter nightsides.