Give meaning to the impossible rotation of Saturn

[ad_1]

According to a new study, Saturn may be doing a small electromagnetic shimmy and a twist that has provoked attempts by scientists to determine the time it takes for the planet to rotate on its axis.

Discovering the duration of a day on any planet seems like a simple task: find a function on the planet and synchronize it when it runs once. Or, if it is a gaseous giant such as Jupiter, which has no solid surface feature, scientists can listen to periodic modulations of the intensity of radio signals created in the rotating magnetic field of the planet.

And then there is Saturn, who for decades defied any attempt to determine its exact rotation period. Now a new study at AGU Journal of Geophysical Research: Space Physics may have finally unveiled the gas giant's trick to hide its rotation, and provide the key to unveiling its secret.

The new research shows how seasonal changes on Saturn can be confusing to scientists trying to calculate their exact rotation period.

The rotation period of a planet is one of the fundamental facts of a planet, with its size, composition, orbital period and other facts that not only describe a planet but help to explain its behavior, history and even provide clues about his training.

Saturn Co.

Saturn transmits only low frequency radio signals that are blocked by the Earth's atmosphere, making it difficult to study Saturn's rotation from the surface of the Earth. On the other hand, Jupiter emits radio diagrams at higher frequencies, which allowed the radio astronomers to determine its period of rotation before the advent of the space age.

Only when spacecraft were sent to Saturn were scientists able to collect data on its rotation. Travelers 1 and 2 sent home the first indications of Saturn's rotation in 1980 and 1981. They detected a modulation of the radio intensity that suggested a rotation of the planet every 10 hours and 40 minutes.

"So this is called the rotation period," said Duane Pontius of Birmingham-Southern College, Alabama, and co-author of the new study.

When the Cassini Space Shuttle arrived in Saturn 23 years later to study the planet for 13 years, she found something amazing.

"Around 2004, we saw that the period had changed by 6 minutes, about 1%," said Pontius.

data-src = "https://scx2.b-cdn.net/" gfx / news / 2019/7-makingsenseo.jpg "data-sub-html =" A mechanical analog model of what could occur with the northern and southern hemispheres of Saturn's atmosphere and magnetospheric plasma to create misleading signals indicating the speed at which the planet is changing The brake is slowing the plasma when it moves away from the planet, in the same way that the arms of a rotating dancer move more slowly when They are extended only when they are held close to the body.Credit: EL Brooks, and others 2019 JGR: Space physics">

<img src = "https://scx1.b-cdn.net/csz/news/800/2019/7-makingenseo.jpg" alt = "Giving meaning to the impossible rotation of Saturn” title=”A mechanical analog model of what could happen with the northern and southern hemispheres of Saturn's atmosphere and the magnetospheric plasma to create misleading signals about the speed of rotation of the planet. The "brake" is the slowing of the plasma that moves away from the planet, in the same way that the arms of a rotating dancer move more slowly when they are extended than when they are held close to the body. Credit: E. L. Brooks, et al, 2019, JGR: Space physics“/>

But how does an entire planet change the speed of its rotation in 20 years? This is the kind of change that takes hundreds of millions of years. Even more mysterious, Cassini's detection of electromagnetic patterns suggesting that the planet's rotation was different in the northern and southern hemispheres.

"For a long time, I assumed something was wrong with the interpretation of the data," Pontius said. "It's just not possible."

Seasons of Saturn

To find out what was really going on, Pontius and his co-authors began by looking at how Saturn was different from his closest brother, Jupiter.

"What is Saturn missing from Jupiter, next to the obvious rings?" Pontius asked. The answer: the seasons. Saturn's axis is tilted about 27 degrees, like the 23-degree inclination of the Earth. Jupiter has virtually no inclination, barely 3 degrees.

The tilt means that the northern and southern hemispheres of Saturn receive different amounts of sunlight depending on the season. The different doses of ultraviolet light affect the polluted atoms – called plasma – located at the edge of Saturn's atmosphere.

According to the model proposed by Pontius and colleagues, the variations of UV from summer to summer in different hemispheres affect the plasma so that it creates more or less drag at altitudes where it meets the gaseous atmosphere of the planet.

This difference in drag slows down the atmosphere, which defines the period observed in the radio signals.

Change the plasma seasonally, and you change the period of radio broadcasts, which is seen on Saturn.

The new model provides a solution to the puzzle of the impossibility of changing the rotation periods of Saturn. It also shows that the periods observed are not the period of rotation of the core of Saturn, which remains unmeasured.

Pontius introduced the model earlier this year at a meeting of Saturn scientists and said he had been well received. Now, he hopes that other researchers will move on to the next step to refine the model by exploring how well it fits the 13 years of Saturn data collected by Cassini.

This story is reissued with the permission of AGU Blogs (http://blogs.agu.org), a community of blogs on Earth and Space Sciences, hosted by the American Geophysical Union. Read the original story here.