AN OVERVIEW OF SATURN’S RINGS

Created by: Angela Patron, Brandi Strieb, Megan McDonald, Allysia Bolt & Sam Whiting

April 2018

Introduction

While the most obvious observation about Saturn may be the fact that it is surrounded by rings, it is important to understand the background of the rings to help fully understand this phenomenon. Diving deeper into the “how” of what we know about Saturn and its rings, also gives us the opportunity to explore the vast layers of science behind our discoveries. By developing a better understanding of the importance of Saturn’s rings, what is already known about these rings, their composition and the research that led us to this conclusion, we can develop a better appreciation of the planet as a whole. When determining what the rings of Saturn are made of, as well as how we know this, we must look at the history of the rings, their composition, the science that led us to this conclusion, the impact these rings have on Saturn, as well as where we are looking to in the future
 

Figure 1. Saturn during Equinox 2008

(Image Credit: https://www.nasa.gov/images/content/365640main_PIA11141_full.jpg )

History

When did we notice the rings of Saturn and what were they first thought to be?
The Discovery of Saturn
The discovery of Saturn holds a significant place in history since the prehistoric era. Saturn is the furthest planet from Earth that is still visible with the naked eye, making its presence in the solar system known since people first investigated the sky.
 
1610: Galileo’s Discoveries
Saturn’s rings however, would not be discovered until 1610 when Galileo Galilei first pointed a telescope towards our sixth planet.1 While Galileo observed Saturn’s rings in 1610 with his 20x magnification telescope,2 he falsely identified the rings as ‘appendages’ or two moons flanking either side of the planet.3 Galileo’s observations of these unknown objects around Saturn became more perplexing as he continued his observations and found the objects to have disappeared a year after his initial discovery. Today, we know that what Galileo was observing over his years of observation was not the disappearance and reappearance of these rings, but what is referred to as the ring plane crossing. The ring plane crossing can be further explained by the tilt of Saturn’s equator and the planet’s rotation around the sun.4

Figure 2. Galileo Galilei. Oil Painting by Justus Sustermans.

(Image Credit: https://commons.wikimedia.org/wiki/File%3AJustus_Sustermans_-_Portrait_of_Galileo_Galilei%2C_1636.jpg)

 
1655: Christiaan Huygens
Dutch astronomer Chrisitaan Huygens, armed with a more powerful telescope than his predecessor Galileo, was able to better observe Saturn. He was able to postulate that the objects surrounding Saturn were a single object, which he explained as being a thin ring.5

1675: Giovanni Cassini
A few decades after Huygens’ discovery, an Italian-French astronomer Giovanni Domenico Cassini expanded on the previous findings. He was able to utilize new advances in telescopes that aided in his discovery of a gap that splits the rings into two sections.8 This addition furthered the field’s understanding that Saturn’s rings were not a single mass, but rather an entire system.

Figure 3. Gian Domenic Cassini

(Image Credit: https://commons.wikimedia.org/wiki/File:B00F_yWCYAEBbIz.png#/media/File:B00F_yWCYAEBbIz.png )

 
1787: Pierre de Laplace
The technology during this period was advancing rapidly which made for a trove of new discoveries. Late 18th century astronomer Pierre de Laplace observed that Saturn’s ring system was comprised of many solid rings, rather than just two rings.7

1856: James Maxwell
Influential physicist James Maxwell furthered this research and discovered that Saturn’s rings were not rings of solid mass, but rather rings composed of various particles.7

Figure 4. James Clerk Maxwell

(Image Credit: https://commons.wikimedia.org/wiki/File%3APSM_V17_D008_James_Clerk_Maxwell.jpg  )

 

Composition

What are the rings of Saturn – What are they made of?
 
Early Theories of Composition
The knowledge we have today of Saturn has not always been so. Early astronomers such as Galileo first developed theories which have either been proved wrong or altered and developed further. When Galileo first seen the rings in 1610 through a telescope, he described them as two arm-like ears sticking out from the planet.17 Later, in 1656 astronomer Christiaan Huygens discovered that the ears were not ears after all but actually circle around the planet in a ring.14 His theory was that Saturn had a solid, thin, flat ring surrounding Saturn.5 New theories have since developed from the early astronomers Galileo and Huygens discoveries.
 
Later Theories
From the theory of a single ring surrounding the planet developed the theory of there actually being multiple rings. French astronomer Jean Chapelain surmised that the rings were made up of small particles orbiting around Saturn, and later the Scottish physicist James Clerk Maxwell confirmed this theory and stated that the particles had to be small or they would be pulled in by Saturn’s gravity until they collided into the planet.17 These astronomers theorized that the rings were created when comets or asteroids collided, shattering into pieces and spreading around the planet.17 Another theory suggests that the rings are composed of debris that failed to clump into moons because of the gravitational pull of Saturn continuously moving the debris around, or possibly the storms and lightning that Saturn produces.16

What research led us to know what the rings are composed of today?
 
As previously mentioned, Galileo was the first astronomer to view Saturn through a telescope around 400 years ago.8 Upon gazing at the planet Saturn, he discovered what he thought to be two “moons” surrounding the planet. These moons turned out to be the rings as we know them today.

Figure 5. Galileo’s initial drawing of Saturn

(Image Credit: www.myastrologybook.com)

Although it was impressive that Galileo was able to discover the rings of Saturn, he was unable to figure out what the rings are made of. In fact, it took another 342 years for humans to be able to test the composition of Saturn’s rings. This was accomplished by G.P. Kuiper in 1952, who used ground-based near-infrared spectroscopy to determine that the rings of Saturn are made up of (or at least covered by) H2O in the form of frost or ice.9 Spectroscopy is the process of determining the makeup of an object by the intensity of different wavelengths that the object absorbs or emits.10 By using spectroscopy, scientists can determine what elements are present in an object.

Figure 6. Labelled Diagram of Saturn

(Image Credit: https://commons.wikimedia.org/wiki/File:Saturn_diagram.svg#/media/File:Saturn_diagram.svg )

Later, in the 1970s and 80s, the first microwave observations of the rings were conducted.11 A microwave observation conducted by Grossman (1990) supported Kuiper’s findings, and even suggested that the rings are made up of almost pure ice with silicate material making up around 1% of the ring’s composition.12 These findings were further supported by the Voyager radio occultation experiment which was performed by Tyler et al. (1983) during the Voyager expeditions.13 The Voyager expeditions refer to a set of twin shuttles that were launched in 1977 to explore the outer planets of our solar system. While the Voyager 1 was passing close to Saturn, G.L. Tyler et al. performed an experiment in which they measured the radio occultation of Saturn’s rings by firing radio signals from the Voyager 1 spacecraft close to earth which travelled through the rings of Saturn to be received by the 64-m-diameter parabolic antenna at the NASA Deep Space Network receiving site near Madrid, Spain.13 They then were able to measure the amount of signal that was cut off by Saturn’s rings and extrapolate information regarding the composition of the rings. The experiment performed by Tyler et al.13 further confirmed the findings of Kuiper that the rings are made up of almost entirely ice.

Figure 7. Cosmic Radio Occultation

(Image Credit: https://www.flickr.com/photos/noaasatellites/29206052983 )

The Composition of Saturn’s Rings
Through these observations and theories, scientists have discovered that in fact the rings of Saturn are composed of particles and debris.17  The debris comes from broken up pieces of comets, asteroids, and dead moons. the particles are made up of ice, dust/mud, and rock.
Along with being able to determine the composition of the rings, scientists have made numerous observations of the rings regarding their size, temperature, placement, and their unique traits. The following list depicts these observations:
Size
*        Particle size varies from the size of a grain of sand to the size of a mountain.14
*        The rings are thin at approximately 33 feet think, reaching up to 2 miles (3km) in some spots.15
*        The rings extend out to 175,000 miles (282,000) from the plant.15
*        The inner moons of Saturn effect the shape of the rings by orbiting between them and dividing them, constraining their width.15
Temperature
*        The Cassini spacecraft took the temperature of the rings on the unlit side and resulted in -264.1° and -333.4° Fahrenheit. (-163° to -203° Celsius).15
Placement
*        The rings are all relatively close to one another with the exception of the Cassini Gap between ring A and ring B that extends 2,920 miles.15
Spokes (unique trait)
*        A unique feature of the rings that essentially look like lines that orbit with the rings called spokes.15
*        One theory is Icy particles above the rings surface via electrostatic charge.15
*        Another theory is that they are electrically charged sheets of dust-sized particles from meteors impacting the rings.5
*        Scientists also speculated that they could be electron beans from Saturn’s lightning.5
*        They are temporary, can form and disappear over a few hours, and discovered by the Cassini mission in 2005.15

Figure 9. Particles above the rings viewed from Cassini on September 22, 2009.

(Image Credit: https://www.nasa.gov/images/content/402560main_cassini20091113-226.jpg )

 

The Names of the Rings

There are in fact seven rings around Saturn, each were given a lettered name in order of their discovery not the order from the planet.15 The order from closest to the planet to farthest is as follows15:
*        D, C, B, A, F, G and E ring

Figure 8. GIF of Saturn’s rings were named in the order they were discovered.

(Image Credit: http://www.jpl.nasa.gov/images/cassini/20161122/rings_diagram_discovery_order.gif)

The Impact

How does the knowledge regarding the rings of Saturn impact our knowledge of Saturn?

When  Saturn’s  rings  were  discovered  almost  400  years  ago,  the  phenomenon shocked scientists. 400 years later, even though we know what these many rings are made of, we still don’t know for certain when they appeared or what caused them to form. Two decades ago NASA’s  spacecraft  Cassini,  began  its  exploration  journey.  In 2017 Cassini returned with some remarkable data. The pictures received from the spacecraft gave great insight into these appealingly changing rings. In 1980 the Voyager spacecraft was sent into space first and sent back pictures of Saturn’s rings. 25  years  later,  one  ring  seemed  to  have  changed,  moving  roughly  200 kilometers inward and became slightly less bright. This discovery gave us the ability to note that the rings are changing, and that we still have much more to discover regarding Saturn, its rings, and other planets.19

The passing of time not only gives us the ability  to study deeper  into  what  we already know, but also gives us the ability to improve technologies that will lead us into future discoveries. If Saturn’s rings are obviously changing over time, then there is a great possibility that other planets are also changing. There could also be other parts of this planet that could
be changing, if we assume that the rings are in fact debris from the planet itself and  these rings are  changing,  then in  turn  the planet itself could be changing. While  Cassini’s  trip  just  recently  ended  after  two  decades  in  space, there are many discoveries that could still be made from the results of this trip. It is also important  to  note  that  Saturn’s  rings  stay  where  they  are  through gravitational forces. However, this gravity is also what pulls pieces into the rings, continuously adding to them. If surrounding particles are able to fall into the rings, then what does this mean for the atmosphere as a whole? Was the solar system once more widely spread out? Were there other smaller planets, or even moons, that Saturn pulled into itself? This idea opens up a wide variety of questions that we still have yet to answer, as well as leads us to question the pull of other planets. Perhaps  there  was  more  to  the  solar  system  at  one  point  than  we  know.18

While the knowledge we have about Saturn and its rings is vast already, the new expedition Cassini tells  us  there  is  much  more  to  learn  about  the  planet  and  the  rings themselves. The gravitational pull of the rings, as well as the new developments found from Cassini leads us into even further possibilities about not only Saturn, but it opens possibilities for new knowledge about other planets that we can find with our ever-developing technology.

Present and Future Research

Where is science and research at now in terms of Saturn’s rings- what is expected for the future? 
 
Science and research is constantly evolving to higher levels of knowledge. Ongoing research is vital to drive innovation and theories to evolve around the solar system for future generations to gain knowledge from. Currently, the research growing around the topic of Saturn and its peculiar rings is comprised of the long-term Cassini project. On October 15, 1997, NASA sent the Cassini spacecraft into orbit to further research the planet Saturn. In July of 2018 the Cassini spacecraft was extended its mission until 2010, and in 2010 for another 7 years. On September 15, 2017, it ended its mission by diving into Saturn’s atmosphere22. The Cassini spacecraft went through the small gap between the deepest visible D-ring and passed through the outer parts of the planet’s atmosphere. Most planetary atmospheres contain a layer that is ionized by incoming solar radiation, referred to as the ionosphere.21 The data collected on site found that Saturn’s ionosphere is very inconstant and interacts with the inner rings of the planet. Figure 10 shows the detailed equipment diagram of the Cassini project.

Figure 10. Labelled Cassini Diagram

(Image Credit: https://commons.wikimedia.org/wiki/File:Cassini-Diagram-No-5.png )

The Langmuir probe is a tool attached to the Cassini, which was created at the Swedish Institute of Space Physics in Uppsala.20 It was used to measure density, temperature, velocity, and particles’ energy, giving a rough estimate of what the gas in the atmosphere consists of.  Strong variations in density showed that the electrically charged part of Saturn’s ionosphere has a strong connection to the rings consisting of ice particles. The ice particles within the rings are therefore also electrically charged. Jan-Erik Wahlund at the Swedish Institute of Space Physics in Uppsala hypothesizes that the small ice particles in the D-ring exhaust electrons from the ionosphere.20 Because of the coupling, electrical flows of gas to and from the rings, along the magnetic field of Saturn, cause the greatest variations in density. This research has also made it recognized that the Saturn A and B-rings protect it from the sun’s EUV radiation and stop the atmosphere in the southern hemisphere from being charged.21 Researchers have observed the decreases in ionization within areas shaded from the Sun by the rings which may lead to future innovative research questions regarding the rings of Saturn.

The following video gives a brief explanation of the Cassini probe dive into Saturn:

https://www.youtube.com/watch?v=W8GhOMrHMkw

Conclusion

By beginning with the history of the rings, their composition, the science to this conclusion, as well as the impact of the rings and where we are headed with our knowledge, we are now able to better grasp the importance of not only what the rings are made of, but how we came to know this. Placing focus on such questions, and such science, gives us the ability to not only know the simple answer to our questions, but also to know the “how do we know” behind this great phenomenon. Knowing this gives us a greater knowledge base for Saturn and other planets, and their equally vast and extraordinary phenomenon’s as well as insight into how they may also work.

Works Cited

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