The James Webb Space Telescope is gazing more and more at exoplanets — worlds orbiting alien stars. Some of them are scorching rocky spheres, tidally locked with one side forever facing their star. There, rock melts into oceans of liquid lava. How does this lava move? The answer matters: by tracking heat flow, astronomers infer the presence of atmospheres using the transit method — when a planet passes in front of its star and slightly dims it.
New simulations compare this ocean to a pot of boiling soup. The stellar wind is a giant spoon, stirring the lava at monstrous speeds up to 360 kilometers per hour. Yet, counterintuitively, the hottest spot right under the star doesn't budge an inch. The reason lies in the shape of the 'pot' itself: the planet's rocky basin prevents heat from spreading sideways.
This finding upends previous thinking. Scientists used to treat a shifted hot spot as a telltale sign of winds or currents. Now it's clear: if JWST detects a shift, the culprit isn't lava but a thick atmosphere or clouds. That means the telescope can more accurately filter out dead planets from those worth a closer look.
Lava flows on such planets can reach 360 kilometers per hour — faster than any ocean current on Earth.
Mustafar from 'Star Wars' is the cinematic go-to for a lava planet.