Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


How long is a day on Saturn?


Measuring the rotation period of a rocky planet like the Earth is easy, but similar measurements for planets made of gas, such as Saturn, pose problems. Researchers from JPL, Imperial College London and UCLA present new results in this week’s Nature (4th May 2006) that may solve the mystery. Using the magnetometer instrument on Cassini, they have found a clear period in the magnetic field of the planet that they believe indicates a day of 10 hours and 47 minutes.

This is a whole 8 minutes slower than NASA Voyager results from the early 1980s, and slower than previous estimates from another Cassini instrument. The magnetometer results provide the best estimate of the Saturn day to date, because it can see deep inside Saturn.

Planets rotate around their “spin” axes as they orbit about the Sun. Rocky planets like the Earth and Mars have rotation periods that remain quite constant and are easy to measure because we can see the surfaces rotate.

Gaseous planets do not have a solid surface to track and are not as rigid as rocky planets. Thus, their periods may change more than those of rocky planets while being less easy to measure. Scientists have sought to use proxy measures such as the repetition rate of radio signals or the period of the rotation of the direction of the magnetic axis of the planet. However for Saturn this has proved difficult because previous missions could not detect a period in the magnetic field measurements and whilst radio data have shown a period – it has changed in the time between previous missions and Cassini.

Since the Voyager days scientists have been seeing changes in the period of radio observations. They knew that it was virtually impossible to slow down or speed up a mass as large as Saturn. As Cassini’s measurements of the rhythms of natural radio signals from the planet continued to vary, scientists began to realize these signals were probably not a direct measurement of the internal rotation rate. Suddenly the length of Saturn’s day became uncertain. Measurements of the magnetic field help scientists “see” deep inside Saturn and may have finally solved this puzzle.

Professor Michele Dougherty of Imperial College London, says “Making this measurement has been one of team’s most important science goals. Finding a period in the magnetic field rotation helps us to understand the internal structure of Saturn’s magnetic fields and from that, of Saturn itself, which will help us understand how the planet formed. After almost two years of collecting data, we are starting to get fascinating insights in Saturn, but we still have more questions than we do answers.”

According to Dr Giacomo Giampieri, a researcher at the Jet Propulsion Laboratory (NASA) and lead author of the paper, Saturn’s rotation posed a great challenge to scientists in the past. In fact, Saturn’s internal magnetic field is almost perfectly aligned with the rotation axis. To explain the consequences of this alignment, Giampieri says to consider a Compact Disc in a CD player.

“Imagine you want to check whether the CD is playing” Giampieri says “If your CD has a label it is easy to see at a glance that it is spinning very fast in the CD player. But if the CD has no label, you would not be able to tell whether the CD is moving or not because it would look static”. Giampieri explains that “Saturn’s magnetic field is similar to a blank CD: if you just look at it, it seems that it is not rotating at all.”

In the past, Pioneer 11 and two Voyager spacecraft encountered Saturn during brief fly-bys and collected data, but no clear periodic signals were found in their magnetic field data. In July 2004 the Cassini spacecraft was inserted into orbit about Saturn and it now has completed many orbits around the gaseous planet. Thanks to the extent of data collected over this extended period of time and the use of appropriate algorithms, a small but regular periodic signature in the magnetic field close to the planet has been detected, with a period of 10 hours 47 minutes and 6 seconds (plus or minus 40seconds). This discovery is like finding a small spot on a CD that allows you to measure how fast it is spinning.

The result is somewhat surprising. Giampieri explains “the period we found from the magnetic field measurements has remained constant since Cassini entered orbit almost 2 years ago, while radio measurements since the Voyager era have shown large variability. By monitoring the magnetic field over the rest of the mission, we will be able to solve this puzzle”.

The periodic signal of Saturn’s magnetic field does not fit simple models for planetary magnetic fields. Giampieri explains “Saturn’s periodic magnetic field differs from that found at Jupiter, which can be modelled as a dipole field tilted with respect to the rotation axis.” This study opens a new perspective on the internal structure and dynamics of Saturn, and how it affects the source of the magnetic field. “We now know that the internal rotation of Saturn and its connection to the external magnetic field is very complex. Our study is the first step in breaking the code” Giampieri says.

Julia Maddock | alfa
Further information:

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Seeking balanced networks: how neurons adjust their proteins during homeostatic scaling.

24.10.2016 | Life Sciences

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

More VideoLinks >>>