Using data from the European Southern Observatory’s Very Large Telescope, astronomers have, for the first time ever, calculated the rotation rate of an exoplanet.

Beta Pictoris b has an equatorial rotation velocity of 100,000 km per hour. How fast is that? Jupiter’s equator has a velocity of about 47,000 km per hour, while Earth’s spins at only 1,700 km per hour. The exoplanet may be 16 times bigger and 3,000 times more massive than the Earth, but a day on the alien world only lasts eight hours.

“It is not known why some planets spin fast and others more slowly,” said co-author Remco de Kok, “but this first measurement of an exoplanet’s rotation shows that the trend seen in the Solar System, where the more massive planets spin faster, also holds true for exoplanets. This must be some universal consequence of the way planets form.”

The astronomers took advantage of a precise technique known as high-dispersion spectroscopy to split light into its basic colors. The principle of the Doppler effect allowed them to use the alteration in wavelength to detect the various parts of the planet traveling at varying speeds and in opposite directions relative to the observer. By deleting the effects of the much more luminous parent star they were able to draw out the rotation signal from the planet.

“We have measured the wavelengths of radiation emitted by the planet to a precision of one part in a hundred thousand, which makes the measurements sensitive to the Doppler effects that can reveal the velocity of emitting objects,” explained lead author Ignas Snellen. “Using this technique we find that different parts of the planet’s surface are moving towards or away from us at different speeds, which can only mean that the planet is rotating around its axis.”