Astronomers studying the speed at which Saturn spins - not an easy task considering the impenetrable gaseous atmosphere covering the planet - say the figure quoted in textbooks needs to be rewritten.

Saturn's "days" - the period of one rotation - are about 6 minutes shorter than what you'll find in current textbooks about our solar system, they say.

While 6 minutes may not seem like a big change, it will cause scientists to drastically change how they think about how winds in the ringed planet's atmosphere blow, says Ravit Helled, a planetary scientist at Tel Aviv University in Israel.

"We used to think that we knew the rotation period," considered a basic property of any planet, she says.

There was never complete agreement, she notes; the Voyager spacecraft that flew past Saturn in the early 1980s measured it as 10 hours and 39 minutes, while the Cassini spacecraft, which went into orbit around the planet in 2004, came up with a figure of 10 hours and 47 minutes.

"Since then, there has been this big open question concerning Saturn's rotation period," says Helled. "In the last few years, there have been different theoretical attempts to pin down an answer."

Helled's team of researchers used Saturn's magnetic field to deduce its spin rate, reporting in the journal Nature a result of 10 hours, 32 minutes and 45 seconds, at least 6 minutes faster than the Voyager measurement.

Those 6 minutes make a big difference, planetary scientists say, since it means Saturn's equator at the level of the atmosphere is spinning 250 miles faster that what the Voyager figure implies, which also affects wind speeds in the atmosphere.

The Voyager figure suggested most winds were blowing in just one direction, while the new result is evidence of around half the winds blowing west and the other half blowing east,  "which seems a little more sensible," says Andrew Ingersoll at the California Institute of Technology in Pasadena, who was not part of the study.

In addition to new insights into the planet's atmosphere and its winds, the new measurements will help scientists understand how the heavy elements in its interior, such as water and rocks, are affected by the speed of the planet's rotation, Helled says.

"The rotation period of a giant planet is a fundamental physical property, and its value affects many aspects of the physics of these planets, including their interior structure and atmospheric dynamics," she says.