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 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.
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"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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