Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers find gravitational wakes in Saturn’s rings

11.11.2005


A diagram of Saturn’s rings illustrating the paths taken by the star Omicron Ceti during four recent occulatations observed by the Cassini spacecraft. Bars at each path show the amount of light that filtered through the rings at points along the occultation. Inset boxes illustrate the orientation of gravitational wakes relative to the direction from the spacecraft to the star at select points in the A ring.


By watching a distant star as it passed behind Saturn’s outer rings, Cornell University astronomers on NASA’s Cassini-Huygens mission to Saturn have found the most direct evidence to date of patterns, called gravitational wakes, within the planet’s outer rings.

The patterns, thin, parallel striations like spokes on a pinwheel, have been theorized since the 1970s, but their small scale (just 100 meters -- 328 feet -- wide) makes them impossible to see even with the spacecraft’s high-resolution camera. The new evidence of their existence, says Phil Nicholson, Cornell professor of astronomy, gives scientists clues about how thick Saturn’s rings are and how their constituent bodies interact.

Nicholson presented his findings in September at the American Astronomical Society’s 37th Division for Planetary Sciences meeting in Cambridge, England.



Nicholson and postdoctoral researcher Matt Hedman used Cassini’s visual and infrared mapping spectrometer (VIMS) to take spectra of the star Omicron Ceti (also known as Mira) in quick succession during four three-hour intervals, or stellar occultations, during which the star passed behind Saturn’s A and B rings. (The A ring is the planet’s outermost visible ring; the B ring is closer to Saturn.) With the more than 100,000 spectra from each occultation, Nicholson and Hedman plotted the amount of near-infrared light that filtered through the rings. They then compared the optical depth -- the amount of light blocked by the ring material -- at several points throughout the occultation. In the comparison, they noticed an unexpected asymmetry: More light filtered through at points on the star’s way out of the occultation than at corresponding points equidistant from the planet on the star’s way in.

At first, Nicholson and Hedman considered whether the asymmetry could be explained by the spacecraft’s slight shift in vantage point over the occultation. But Nicholson pointed out that the distance between the spacecraft and the star is virtually infinite. Lines drawn between the two at either end of the occultation are for all practical purposes parallel -- so the angle between the ring plane and the line of sight between Cassini and the star doesn’t change significantly.

More likely, said Nicholson, is that the small chunks of water ice that comprise the rings are arranged in stripes radiating outward at a skewed angle, like spokes on a pinwheel. The so-called gravitational wakes form when the small objects’ gravitational attraction to each other competes with the tendency of tidal forces from Saturn to pull them apart.

"When the wakes are seen almost end on, the A ring appears at its most transparent," said Nicholson, "whereas when the wakes are seen from the side, the ring becomes almost opaque."

Though Cassini, which arrived at the giant planet in June 2004, can’t get close enough to see the wakes directly (the spacecraft was about 1.6 million kilometers away from Saturn when the occultations occurred), Nicholson has already heard from other Cassini researchers with independent observations supporting the existence of gravitational wakes.

"I suspect in the end that many Cassini instruments will be seeing the same kind of phenomenon," he said. Still, while he expected some evidence of the wakes, the spacecraft’s position during the occultations -- with only 3.5 degrees between the ring plane and the line of sight to the star -- made the effect striking.

"We were certainly surprised," he said. "We were not expecting it to be as obvious. At one level, it’s just kind of neat to us who study rings. For those of us in the business it’s nice to get direct evidence of the wakes."

On a more practical level, though, the finding gives scientists a new piece of information about the rings’ micro-structure and internal dynamics: specifically, how the ice chunks move as they are pulled toward each other and collide, and as Saturn’s tidal force shears them apart again.

It also gives researchers a tool for judging the overall thickness of Saturn’s rings. Throughout Cassini’s four-year mission, astronomers will collect data from dozens of similar experiments. Since each will be made from a different viewing angle, astronomers will then compare how marked the wakes’ effect is across the series. That information will allow them to estimate the rings’ thickness (their north-south span) -- which is thought to be as little as 10 meters -- 33 feet.

Using the wakes to estimate the rings’ thickness is similar to using sunlight to estimate the widths of slats on a set of vertical blinds. If the blinds are open and the sun is high in the sky, the blinds will let in nearly all the light. But as the sun sets to one side, the blinds -- in the same position -- will begin to block more and more light, because of their width. Similarly, if the rings are very thick, the spacecraft will continue to see the wakes’ effect from higher elevations; if they are very thin, evidence of the wakes will begin to diminish when the angle between Cassini’s line of sight and the ring plane is still quite small.

"This may be the best way of directly learning the thickness of the rings," Nicholson said.

Cassini’s VIMS team is led by Robert Brown at the University of Arizona’s Lunar and Planetary Laboratory. During Cassini’s Saturn tour, the spacecraft will complete 74 orbits of the planet, 45 flybys of the moon Titan and many flybys of Saturn’s other moons.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL.

Technical details: The observations were made on May 24, June 11, June 29 and Aug. 5, 2005, and the data shown here were obtained at a wavelength of 2.92 microns. At this wavelength the brightness of the icy rings themselves is at a minimum, permitting the star to be seen most clearly. The brightness of omicron Ceti was measured once every 80 milliseconds, during which time the star moved approximately 1.2 km across the rings. The apparent diameter of the star, as projected onto the ring plane, was about 4 km, so that each individual measurement represents an average over many individual wakes. For each occultation, between 106,000 and 192,000 individual spectra were recorded.

Credits: The VIMS instrument is operated by the University of Arizona. Data analysis by P.D. Nicholson, M.M. Hedman (Cornell University). Inset diagrams by Heikki Salo, Oulu University.

Lauren Gold | EurekAlert!
Further information:
http://www.news.cornell.edu/stories/Nov05/Nicholson.Cassini.lg.html
http://www.cornell.edu

More articles from Physics and Astronomy:

nachricht NASA's SDO sees partial eclipse in space
29.05.2017 | NASA/Goddard Space Flight Center

nachricht Strathclyde-led research develops world's highest gain high-power laser amplifier
29.05.2017 | University of Strathclyde

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: Strathclyde-led research develops world's highest gain high-power laser amplifier

The world's highest gain high power laser amplifier - by many orders of magnitude - has been developed in research led at the University of Strathclyde.

The researchers demonstrated the feasibility of using plasma to amplify short laser pulses of picojoule-level energy up to 100 millijoules, which is a 'gain'...

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

New insights into the ancestors of all complex life

29.05.2017 | Earth Sciences

New photocatalyst speeds up the conversion of carbon dioxide into chemical resources

29.05.2017 | Life Sciences

NASA's SDO sees partial eclipse in space

29.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>