On planets billions of miles away, fluffy clouds made of vaporized rocks and salt are doing something surprising: they're melting the ground beneath them.
Scientists at Arizona State University have discovered that clouds on a type of planet called sub-Neptunes can raise temperatures deep inside those worlds by more than 1,400 degrees Celsius. That's hot enough to turn solid rock into liquid magma oceans.
Sub-Neptunes are the most common type of planet in our entire galaxy. They're bigger than Earth but smaller than Neptune, and nobody really knows what they're made of. They could be rocky worlds wrapped in thick hydrogen gas, or they could be loaded with water and carbon-based molecules. Scientists want to answer that question, especially using the powerful James Webb Space Telescope, which can study the atmospheres of planets orbiting distant stars.
But there's a catch: the telescope only sees the top layers of these planets' atmospheres. The interesting stuff—what the planet is actually made of—lies hidden far below.
Now, a team led by Sagnick Mukherjee, a postdoctoral researcher at Arizona State University, has found that clouds make this puzzle even trickier. Using detailed computer models, Mukherjee's team discovered that clouds of vaporized rocks and salts don't just block our view—they actively change what's happening inside the planet. These clouds act like a warm blanket, trapping heat that tries to escape from the interior and driving temperatures much higher than scientists previously expected.
For the sub-Neptunes they modeled, accounting for these clouds raised temperatures in the deeper atmosphere by more than 1,000 degrees Celsius while actually cooling the upper layers. That temperature shift reaches all the way down to where the atmosphere meets the planet's interior.
For two specific planets called GJ 1214 b and TOI-12C31 b, that added heat is enough to melt the rocky surface solid. "For some of the planets we modeled, that extra heat is enough to melt the planet's surface, creating a magma ocean," said co-author Matthew Nixon, also at Arizona State University.
This matters because a magma ocean isn't just a cool geological fact. Like volcanoes on Earth, it can swap gases between the planet's molten interior and its outer atmosphere, changing the chemistry of the sky above. That means when scientists look at a sub-Neptune's atmosphere with the James Webb Space Telescope, the chemicals they find might not accurately reflect what the planet is truly made of.
"Interpreting JWST observations of sub-Neptunes is particularly challenging," said co-author Luis Welbanks, an assistant professor at Arizona State University. "This work takes us one step closer to answering the question of what these mysterious worlds are made of."
So while clouds may have seemed like a nuisance blocking our view of distant worlds, it turns out they're actually keys to understanding them—despite making the science far more complicated.