Cassini finds Saturn sends mixed signals

Mar 23, 2011 By Jia-Rui Cook
This unique image from NASA/ESA's Hubble Space Telescope from early 2009 features Saturn with the rings edge-on and both poles in view, offering a stunning double view of its fluttering auroras. Credit: NASA/ESA/STScI/University of Leicester. Image credit: NASA/ESA/STScI/University of Leicester

(PhysOrg.com) -- Like a petulant adolescent, Saturn is sending out mixed signals.

Recent data from NASA's show that the variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres. Moreover, the northern and southern rotational variations also appear to change with the Saturnian seasons, and the hemispheres have actually swapped rates. These two radio waves, converted to the human audio range, can be heard in a new video:

This video is not supported by your browser at this time.
Saturn is sending out mixed signals in recent data from NASA's Cassini spacecraft and the NASA/ESA Hubble Space Telescope. (NASA)

"These data just go to show how weird Saturn is," said Don Gurnett, Cassini's radio and plasma wave science instrument team lead and professor of physics at the University of Iowa, Iowa City. "We thought we understood these radio wave patterns at gas giants, since Jupiter was so straightforward. Without Cassini's long stay, scientists wouldn't have understood that the radio emissions from Saturn are so different."

Saturn emits radio waves known as Saturn Kilometric Radiation, or SKR for short. To Cassini, they sound a bit like bursts of a spinning air raid siren, since the radio waves vary with each rotation of the planet. This kind of radio wave pattern had been previously used at Jupiter to measure the planet's rotation rate, but at Saturn, as is the case with teenagers, the situation turned out to be much more complicated.

When NASA's visited Saturn in the early 1980s, the radiation emissions indicated the length of Saturn's day was about 10.66 hours. But as its clocking continued by a flyby of the joint ESA-NASA Ulysses spacecraft and Cassini, the radio burst varied by seconds to minutes. A paper in in 2009 analyzing Cassini data showed that the Saturn Kilometric Radiation was not even a solo, but a duet, with two singers out of sync. Radio waves emanating from near the north pole had a period of around 10.6 hours; radio waves near the south pole had a period of around 10.8 hours.

A new paper led by Gurnett that was published in Geophysical Research Letters in December 2010 shows that, in recent Cassini data, the southern and northern SKR periods crossed over around March 2010, about seven months after equinox, when the sun shines directly over a planet's equator. The southern SKR period decreased from about 10.8 hours on Jan. 1, 2008 and crossed with the northern SKR period around March 1, 2010, at around 10.67 hours. The northern period increased from about 10.58 hours to that convergence point.

Seeing this kind of crossover led the Cassini scientists to go back into data from previous Saturnian visits. With a new eye, they saw that NASA's Voyager data taken in 1980, about a year after Saturn's 1979 equinox, showed different warbles from Saturn's northern and southern poles. They also saw a similar kind of effect in the Ulysses radio data between 1993 and 2000. The northern and southern periods detected by Ulysses converged and crossed over around August 1996, about nine months after the previous Saturnian equinox.

Cassini scientists don't think the differences in the radio wave periods had to do with hemispheres actually rotating at different rates, but more likely came from variations in high-altitude winds in the northern and southern hemispheres. Two other papers involving Cassini investigators were published in December, with results complementary to the radio and plasma wave science instrument -- one by Jon Nichols, University of Leicester, U.K., in the same issue of Geophysical Research Letters, and the other led by David Andrews, also of University of Leicester, in the Journal of Geophysical Research.

In the Nichols paper, data from the NASA/ESA Hubble Space Telescope showed the northern and southern auroras on Saturn wobbled back and forth in latitude in a pattern matching the radio wave variations, from January to March 2009, just before equinox. The radio signal and aurora data are complementary because they are both related to the behavior of the magnetic bubble around Saturn, known as the magnetosphere. The paper by Andrews, a Cassini magnetometer team associate, showed that from mid-2004 to mid-2009, Saturn's magnetic field over the two poles wobbled at the same separate periods as the and the aurora.

"The rain of electrons into the atmosphere that produces the auroras also produces the radio emissions and affects the magnetic field, so scientists think that all these variations we see are related to the sun's changing influence on the planet," said Stanley Cowley, a co-author on both papers, co-investigator on Cassini's magnetometer instrument, and professor at the University of Leicester.

As the sun continues to climb towards the north pole of , Gurnett's group has continued to see the crossover trend in radio signals through Jan. 1, 2011. The period of the southern radio signals continued to decrease to about 10.54 hours, while the period of the northern radio signals increased to 10.71 hours.

"These papers are important in helping to explain the complicated dance between the sun and Saturn's magnetic bubble, something normally invisible to the human eye and imperceptible to the human ear," said Marcia Burton, a Cassini fields and particles scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who was not involved in the work. "Cassini will continue to keep an eye on these changes."

Explore further: European Data Relay System on track

Related Stories

Discovery of Saturn's auroral heartbeat

Aug 04, 2010

(PhysOrg.com) -- An international team of scientists led by Dr Jonathan Nichols of the University of Leicester has discovered that Saturn’s aurora, an ethereal ultraviolet glow which illuminates Saturn’s ...

Researchers present Cassini findings at Saturn

Dec 17, 2004

NASA's Cassini spacecraft approached Saturn last July, it found evidence that lightning on Saturn is roughly one million times stronger than lightning on Earth. That's just one of several Cassini findings that University ...

Cassini Sees Lightening on Saturn

Apr 14, 2010

(PhysOrg.com) -- NASA's Cassini spacecraft has captured images of lightning on Saturn. The images have allowed scientists to create the first movie showing lightning flashing on another planet.

Recommended for you

Cassini sees sunny seas on Titan

8 hours ago

(Phys.org) —As it soared past Saturn's large moon Titan recently, NASA's Cassini spacecraft caught a glimpse of bright sunlight reflecting off hydrocarbon seas.

Is space tourism safe or do civilians risk health effects?

12 hours ago

Several companies are developing spacecraft designed to take ordinary citizens, not astronauts, on short trips into space. "Space tourism" and short periods of weightlessness appear to be safe for most individuals ...

An unmanned rocket exploded. So what?

14 hours ago

Sputnik was launched more than 50 years ago. Since then we have seen missions launched to Mercury, Mars and to all the planets within the solar system. We have sent a dozen men to the moon and many more to ...

NASA image: Sunrise from the International Space Station

15 hours ago

NASA astronaut Reid Wiseman posted this image of a sunrise, captured from the International Space Station, to social media on Oct. 29, 2014. Wiseman wrote, "Not every day is easy. Yesterday was a tough one. ...

Copernicus operations secured until 2021

16 hours ago

In a landmark agreement for Europe's Copernicus programme, the European Commission and ESA have signed an Agreement of over €3 billion to manage and implement the Copernicus 'space component' between 2014 ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.