As the planet continues to cool and shrink, it spin is expected to rev up, just as a spinning ice skater speeds up when she pulls her arms in. Snellen’s team estimates that over hundreds of millions of years, the planet will increase its spin to 40 kilometres a second, giving it a sunset every three hours.

The measurement of the planet's spin is consistent with a trend seen in the Solar System: with the exception of Mercury and Venus, more massive planets tend to rotate faster. This may be because the more massive the planet, the more material it accretes, which imparts additional spin, during their final stages of formation. But the notion that rocky planets such as Earth have the same relationship between mass and rotation as gas giants like β Pictoris b and Jupiter is a puzzle, says Snellen, since the two types of planet pack material on in different ways.

Determining spin is the necessary first step in constructing weather maps of the atmospheres of young, Jupiter-size exoplanets, says Ian Crossfield of the Max Planck Institute for Astronomy in Heidelberg, Germany. Changes in the absorption spectra of a planet as it rotates may indicate the presence of clouds in its atmosphere, he explains. Earlier this year, he and his colleagues used this method to make the first weather map of a rotating brown dwarf3. His upcoming paper in Astronomy & Astrophysics4 assesses the ability to make similar maps for Jupiter-size planets, which will require the next generation of giant, ground-based telescopes.

Source and special thanks: Nature