Fixed above Saturn’s north pole is something as beguiling as Jupiter’s Great Red Spot: a hexagonal storm kept in place by a peculiar jet stream. Now, planetary scientists say that the rotation of the hexagon could most accurately reflect the length of Saturn’s short-lived day: 10 hours, 39 minutes, and 23 seconds. Like the other gas giants, Saturn lacks a solid surface that can be used to measure its rotation period; surficial atmospheric features at the equator move faster than at the poles. Many planetary scientists use magnetic-field radio emissions as a way to calculate the rotation period, because those emissions are assumed to originate from deep within the planet’s interior, where the rotation period is more constant. At Saturn, however, this technique has proved to be problematic: Those emissions differ by about 15 minutes between the northern and southern hemisphere. The hexagon could be the key to a more constant rotation rate. Publishing in Geophysical Research Letters, researchers combined images from the Cassini spacecraft spanning 5.5 years and found that the hexagon’s rotation period barely changed. They suggest that the storm, which could extend hundreds of kilometers below the surface, is intimately coupled with the interior, and therefore a good marker for the planet’s true rotation period.