Measuring Saturn’s Speedy Rotation

How do we measure the rotation speed of a planet? Exactly as you would expect.  Watch the surface, look for markable features, and time how long it takes until those features pass the same point again in the future.  But how can we possibly nail down this information when the planet has little to no visible surface features.  Gas giant planets are great examples of this.  Jupiter is a bit easier since it has plenty of storms and separated cloud layers along the planet’s rotation axis, but the other three are much tougher.  Aside from hard-to-spot features, gas giants also sport different rotation speeds that vary with latitude.  A new method for measuring Saturn’s speed has been determined, and it gives us extra information important to our understanding.

Credit: NASA/JPL

In the past, astronomers have looked at fluctuations in radio radiation measurements resulting from the magnetic field of gas giants such as Saturn, but for Saturn this has resulted in different rotation speeds over a history of measurements.  The new method, from Tel Aviv University researcher Dr. Ravit Helled, utilizes a statistical work-up based on properties we already have figured out, such as Saturn’s gravitational field and shape.  By applying known properties to the equations to constrain the results, Dr.Helled’s team was able to narrow down the rotation period of the planet that matched the majority of solutions to the equations.

To test their solution, they applied the same equations to Jupiter, and found that their result matched the accepted and verified results for Jupiter.  It looks like everything is working perfectly.

The best part about Dr. Helled’s method is that the results give insights into other important properties of Saturn.  “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,” said Dr. Helled. “We were determined to make as few assumptions as possible to get the rotational period. If you improve your measurement of Saturn’s gravitational field, you narrow the error margin.”

The team hopes to apply their new method to Uranus and Neptune in the future, in order to better understand the gas giants that guard our outer solar system.

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