For decades, scientists have been struggling to determine how long exactly does a Saturn day last. While measuring how long it takes for a full axis rotation may be easy in case of solid planets like Mars or Earth, things get a bit trickier when it comes to the gas giant. However, a group of Israeli scientists claims to have come with the exact measurement.
Gas giants like Saturn lack a solid surface feature than can be easier tracked to determine to determine the length of a day. Saturn’s surface is covered instead by a thick layer of clouds, continuously on the move, so any visual measurement has to be ruled out first.
Resorting to chemistry doesn’t help much either. Different speeds were registered for the rotations of hydrogen and helium elements, so keeping track of the properties of the different types of gas forming Saturn is not a solution.
Planetary scientists from the Tel Aviv University in Israel, led by Dr. Ravit Helled, claim to have found the right approach to solve the dilemma. The calculations they made relied instead on studying Saturn’s specific gravitational field and the planet’s unique feature of having a shorter east-west axis than the north-south axis.
Precise day measurement is tough business
When Voyager 2 visited Saturn in 1981, the scientific world was convinced the planet had a rotation period of 10 hours and 39 minutes, according to measurements the probe made. But NASA’s Cassini spacecraft, who reached Saturn some thirty years later, sent home different numbers, initially estimating it took the planet 8 minutes longer to make a full rotation on its axis.
What really puzzled the scientists is that each time Cassini took a new measurement, the numbers were different. It quickly became obvious that the method employed by both Voyager and Cassini, which involved focusing on Saturn’s radio radiation, was not to be trusted. “It was then understood that Saturn’s rotation period could not be inferred from the fluctuations in radio radiation measurements linked to Saturn’s magnetic field, and was in fact still unknown,” Dr. Helled explained.
Scientists then tried to come up with a third theory to find out how long a day lasts on Saturn, but the gas giant didn’t like this one either. For some planets, their magnetic field’s axis tends to tilt when compared to the planet’s spin axis, and measuring the difference can give the answer. But in the case of Saturn, the two line up perfectly, and no deduction can be made.
Dr. Helled and her team took a more mathematical approach and believe they have found the right answer. “We came up with an answer based on the shape and gravitational field of the planet. We were able to look at the big picture, and harness the physical properties of the planet to determine its rotational period,” the Israeli scientist explained.
By studying Saturn’s gravity field, Dr. Helled finally came with a result. Her report was published online on Wednesday, in Nature Science Journal, and claims Saturn makes a complete spin 10 hours and 32 minutes and 45 seconds, with a margin of error of 46 seconds. Still, it’s over 6 minutes longer than what Voyager came up with thirty years ago.
How long do 6 minutes really mean? Well, for a planet the size of Saturn, it’s a big difference. According to planetary scientist Andrew Ingersoll, with the California Institute of Technology in Pasadena, a six minute difference actually means the planet’s atmosphere must spin 400 kilometers per hour faster that initially estimated.
While the discovery is not really earth-shattering news for the scientific community, it certainly helps by settling a decade long debate.
Image Source: Sciencemag
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