By Will Dunham
WASHINGTON, April 30 (Reuters) - Are you the type of person who gets dizzy just watching a merry-go-round go round and round? If so, don't plan a visit to the planet known as Beta Pictoris b. The thing spins like mad.
Scientists said on Wednesday that for the first time, they have measured the spin of a planet outside our solar system - a large gas planet located a relatively close 63 light years from Earth.
They determined that the planet spins faster than any in our solar system, with a rotational velocity at its equator of about 56,000 miles per hour (almost 100,000 kph).
Jupiter, a large gas planet that has the quickest spin in our solar system, whirls at about 29,000 miles per hour (47,000 kph) while Earth spins at about 1,000 miles per hour (1,700 kph). A day on Beta Pictoris b lasts only eight hours, compared to 10 hours for Jupiter and 24 hours for Earth.
Scientists have spotted about 1,800 planets beyond our solar system, but very little is known about these distant worlds including the basics like what they are made of and how they travel around their stars.
Beta Pictoris b is one of the better understood of these planets. It is one of only about a dozen that have been directly observed rather than found using indirect detection methods in which scientists can only see the planet's influence on the host star.
"Only if we know more about other planets - like temperatures, atmosphere and rotation - can we tell how unique our home in the universe really is," said one of the researchers, Bernhard Brandl, an astronomy professor at the University of Leiden in the Netherlands.
Beta Pictoris b is big, hot and young. It is about 3,000 times more massive than Earth and seven times more massive than Jupiter, our solar system's largest planet. It is only about 20 million years old, compared to about 4.5 billion years for Earth, and is still hot from its formation, the scientists said.
Its host star, Beta Pictoris, is approximately twice as massive and 10 times as luminous as our Sun.
The head-spinning speed at which Beta Pictoris b whirls, the scientists said, lends support to the notion that a planet's rotational velocity is closely related to its size: the bigger, the faster.
"Yes, the relation between mass and spin velocity was already known in our solar system," said University of Leiden astronomy professor Ignas Snellen, another of the researchers.
"We now extend it to a more massive planet to see that the relation still holds. We need to observe more planets to confirm this is really a universal law," Snellen added.
The technique the scientists used to measure the planet's spin was based on the Doppler effect, the well-known phenomenon people notice when they hear a change in the pitch of an ambulance siren when the vehicle whizzes by.
"When we observe a rotating planet, the light from one half, which is approaching us, has a slightly different frequency, or color, than the other half, which is receding from us. The relative difference in color, or frequency, between the two halves is a measure of the spin-rotation velocity," Brandl said.
Beta Pictoris b is located in the southern constellation of Pictor and was discovered about six years ago. It orbits eight times farther from its host star than Earth orbits the Sun.
The scientists are hoping in the future to make a global map of it including possible cloud patterns and storms.
The research was published in the journal Nature. (Reporting by Will Dunham)
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