Beta Pictoris b is the first alien planet to have its rotation speed successfully clocked by astronomers.
The eight-hour day of Beta Pictoris b, a gas giant roughly 10 times the size of Jupiter, is thanks to its quick rotational speed. The equator of Beta Pictoris b spins around the planet's axis at a rate of 62,000 mph, much faster than any other planet in our solar system.
By comparison, Jupiter's equator rotates at a rate of 29,000 mph, and Earth's equator spins at a speed of 1,060 mph.
"It is not known why some planets spin fast and others more slowly, 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," said study co-author Remco de Kok, an astronomer at the Leiden Observatory in the Netherlands. "This must be some universal consequence of the way planets form."
The planet in question orbits Beta Pictoris, a star which lies some 63 light-years from Earth and can be seen with the naked eye in the southern sky constellation Pictor, Latin for "The Painter’s Easel."
Because of the planet's exceptional rotation speed and gaseous state, it features an apparent oblong shape -- disproportionally wider at its center than toward its poles.
The astronomers used a analysis technique called "high-dispersion spectroscopy" sourced with readings from the European Southern Observatory's Very Large Telescope.
"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."