How can the rotational speed of a whole planet alter in 20 years? That kind of shift takes hundreds of millions of years to occur.
The Cassini Mission's discovery of electromagnetic signals that showed that Saturn rotates differently in its northern and southern hemispheres was even more puzzling. “For a long time, I assumed there was something wrong with the data interpretation,” said astrophysicist Duane Pontius. “It’s just not possible.”
Revealing the gas giant's rotational concealment technique
Saturn has resisted efforts to determine its precise rotation period for many years. Recent research published in the Journal of Geophysical Research: Space Physics of the American Geophysical Union may have finally discovered the gas giant's trick for concealing its rotation and provided the solution to revealing its secret.
The latest study demonstrates how Saturn's seasonal variations could be complicating scientists' efforts to determine the planet's precise rotation cycle.
Finding a feature on the planet and timing it as it completes one rotation seems to be the simple method for determining the duration of a day on any planet. Alternatively, if the object is a gas giant like Jupiter, which lacks any obvious surface characteristics, researchers may keep an eye out for regular variations in the strength of radio waves produced by the planet's revolving magnetic field.
One of the basic facts about a planet is its rotation period. Other fundamental facts about a planet include its size, composition, orbital period, and other features that not only characterize it but also aid in explaining its behavior, history, and even its formation.
Cassini Discovers Something Astonishing
It is difficult to see Saturn's rotation from the surface of the Earth because Saturn only produces low-frequency radio signals that are obstructed by the atmosphere. Prior to the space age's full development, radio astronomers were able to determine Jupiter's rotation period thanks to its higher frequency radio emission.
Science wasn't able to gather information on Saturn's spin until spacecraft were deployed there. In 1980 and 1981, Voyagers 1 and 2 sent the first indications of Saturn's rotation to Earth. A change in radio strength they discovered indicated that the planet spins once every 10 hours, 40 minutes.
“So that was what was called the rotation period,” said Pontius of Birmingham-Southern College in Alabama and a co-author of the new study.
23 years later, the Cassini mission, which would spend 13 years studying Saturn, made an astounding discovery. “In about 2004 we saw the period had changed by 6 minutes, about 1 percent,” Pontius said.
The Plasma “Brake”
Saturn's upper atmosphere contains plasma, which is ionized gas linked to the planet's magnetic fields. The lowest layers of the atmosphere lose angular momentum as the charged particles that make up the plasma travel upward along the magnetic field lines.
Plasma slows down when it travels away from the globe via a process known as "magnetic braking," similar to how a spinning dancer's arms move more slowly when they are extended than when they are kept close to the body. Our Sun was once spinning roughly five times faster than it is now, but it has now slowed down as a result of billions of years of magnetic braking.
Saturn's age cannot be explained by a consistent 1% variation in rotation rate every ten years, however. The apparent variations in Saturn's rotation rate must also be caused by some other activity.
The Seasons
Pontius and his co-authors began their investigation into the situation by examining how Saturn differs from its nearest brother, Jupiter.
“What does Saturn have that Jupiter lacks, besides the obvious rings?” Pontius enquired. Seasons are the solution. Similar to Earth's 23-degree tilt, Saturn's axis is slanted by around 27 degrees. Only 3 degrees of tilt may be found on Jupiter.
Due to its tilt, Saturn's northern and southern hemispheres receive varying quantities of solar radiation depending on the time of year. The plasma at the outer edge of Saturn's atmosphere is impacted by the various UV light dosages.
The hypothesis put up by Pontius and his colleagues state that the plasma is affected by the differences in UV from summer to winter in the various hemispheres, causing it to produce more or less drag at the altitudes where it hits the planet's gaseous atmosphere.
The atmosphere slows down due to the difference in drag, which determines the period in the radio transmissions. On Saturn, the radio emissions are seen to shift in duration as the plasma changes seasonally.
The new model offers an answer to the riddle of Saturn's seemingly irrational fluctuating rotation periods. It also demonstrates that the rotation period of Saturn's core, which is yet unknown, is not represented by the recorded periods.
Reference(s): DailyGalaxy