If you’re planning a picnic on a hot Jupiter exoplanet this weekend, you might want to pack a heavy-duty umbrella. According to an astronomical weather report, the night sides of these planets might have pretty rocky weather – and we mean that literally. Thick clouds of vaporized minerals could be raining rocks.
Astronomers are no strangers to these kinds of wild weather reports. In the past these predictions have painted pictures of planets where it rains glass, or snows despite blistering hot weather, where winds whip around at 8,700 km/h (5,400 mph), and clouds might be made of ruby and sapphire.
In the latest such report, astronomers from McGill University used the Spitzer and Hubble Space Telescopes to examine the weather on 12 “hot Jupiters” – gas giant exoplanets that orbit very close to their host stars.
These particular planets are all tidally-locked, meaning one side always faces the star while the other is draped in perpetual darkness. As you’d expect, the day side of these planets is extremely hot, and while the night sides are a tad cooler, they’re still hot enough to melt lead several times over.
But what really surprised the researchers is just how consistent those nighttime temperatures were across the 12 exoplanets. The team found that all of them hovered around 800° C (1,472° F).
“Atmospheric circulation models predicted that night side temperatures should vary much more than they do,” says Dylan Keating, first author of the study. “This is really 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 1,700°C (3,060° F).”
So what’s causing these temperatures to be so consistent? The team suggests that cloud cover is to blame, forming a thick blanket that blocks heat from radiating out into space where it can be detected. But these aren’t just any old clouds – they’re made of rock, vaporized by the intense temperatures of the day side before wind brings them around to the dark side. There the cooler temperatures make them condense into clouds, and possibly a rocky rainfall.
“The uniformity of the nightside temperatures suggests that clouds on this side of the planets are likely very similar to one another in composition,” says Keating. “Our data suggest that these clouds are likely made of minerals such as manganese sulfide or silicates, or rocks.”
The team says that further observations of these hot Jupiters in different wavelengths will help astronomers determine what these clouds actually are.
The research was published in the journal Nature Astronomy.
Source: McGill University