Saturn’s Auroras & Enceladus
By: Dayton Smith, Elizabeth Erker, Kayli Rusnak, Keyara Greyeyes, Shelby Cheveldayoff, and Brendan Checkosis
Introduction and background
Saturn is the sixth planet from the sun and is considered a gas giant. It is the second largest planet in our solar system and also the least dense. Saturn is surrounded by 52 confirmed moons with 29 additional moons awaiting confirmation.1 Saturn’s rings are comprised of comets, asteroids, or broken rock particles.2 Interesting enough, Saturn does have auroras like Earth that do occur on the southern pole of the planet, which will be analyzed further in this paper.
Little was known about Saturn before 1979. Analyzing the space crafts that made the discoveries of Saturn will be considered within this research paper and the contributions the spacecrafts have made to what we know about Saturn. It was determined that the auroras were not visible to the naked eye, images of Saturn’s auroras is credited to the images and data the spacecrafts were able to receive. It would be determined that one of Saturn’s moons would determine the auroras composition.
Enceladus, one of Saturn’s many moons, will be analyzed because of its electronic effect on Saturn’s auroras: proton activity from Enceledes injected into Saturn’s atmosphere.3 Saturn’s magnetic field is unique in the sense that it is a product of the planets surroundings which causes the Auroras, which Enceledes effects the atmosphere in its entirety. Also, much of the motivation of the proceeding research will have to do with uncovering Saturn’s auroric function in relation to the planet and the planets unique relationship with Enceledes. Therefore, the Auroras functions will be analyzed in regard to the information humans have received from spacecrafts sent into orbit and how the auroras functions are determined by the planets atmospheric function in relation to Enceledus.
Discovery of Saturn’s Auroras
Pioneer & Voyager
The spacecraft Pioneer 11 first discovered the auroras on Saturn in 1979 when far-ultraviolet brightening was observed on Saturn’s poles.4
In the early 1980’s Voyager 1 and 2 did flybys of Saturn, and found ultraviolet emissions of hydrogen at mid-latitudes that are similar to auroras and at polar latitudes found actual auroras.5
The Hubble Telescope obtained images of the auroras for the first time in 1994.6 In order to view and photograph the auroras the Hubble telescope uses the Space Telescope Imaging Spectrograph, which uses spectroscopy.7 The instrument is able to detect ultraviolet light due to how sensitive it is to a wide range of wavelengths of light.7
Cassini was the next spacecraft to give more information on the auroras of Saturn. Cassini was launched in 1997 and became the first spacecraft to orbit Saturn in 2004.8
The Cassini spacecraft has many instruments including Composite Infrared Spectrometer, Imaging Science Subsystem, Magnetospheric Imaging Instrument and Ultraviolet Imaging Spectrograph which all contribute to our new understanding of how the auroras work on Saturn.9
The composite infrared spectrometer captures infrared light and splits it into its different wavelengths, this is used to measure temperature and the composition of what something is made of.9
The Imaging Science Subsytem is made up of a wide angle camera and a narrow angle camera, these cameras were sensitive enough to capture some ultraviolet and infrared light.9
Using three sensors the Magnetospheric imaging instrument detects charged particles of Saturn’s magnetosphere, this instrument was used to observe how Saturn’s magnetosphere interacts with solar winds, the atmosphere, its rings and moons.9
Creation of Auroras
The creation Auroras themselves begins when the electromagnetic fields on the sun get tangled and they explode. This causes the sun’s surface to heat up and create sunspots, where the surface bubbles and releases charged gas called solarwinds.10 When these solar winds reach earth some of them interact with our planets atmosphere and the gases within which creates the auroras.11 This light is because the photons from the sun have high energy and are absorbed by the electrons in our atmospheric gases which cause the electrons to enter an energized state. Eventually the electron returns to its ground state and releases the photon, the photon is related to with the corresponding wavelength of the energy it expelled and creates the lights in the colours we recognize as the Aurora Borealis and the Aurora Australis (Aurora at the southern pole).
This means that other planets also have the ability to have auroras, such as Jupiter, although the process is slightly different. On Jupiter it is believed to be caused by Jupiter’s large electric potential due to its size is causing particles to be accelerated and creating colours when entering Jupiter’s atmosphere. Saturn also has its own unique interactions to cause its aurora.
The auroras occur at the poles of planets because that where the magnetic field tends to be the weakest this is helped as the earth’s magnetic field deflects the particles around the planet until they eventually reach the poles.12
With the recent information obtained from the cassini probe there is now much more information about known about the Aurora borealis on Saturn. Firstly, it is only visible as only ultraviolet light.13 Interestingly Saturn’s Aurora is different from both Jupiter’s and Earth’s, as Saturn’s is very variable in size (can become extremely large) and can pass in only 45 minutes. It is believed that Saturn’s aurora is caused in main part by the planets solar winds interacting with its atmosphere. It also seems that Saturn moon Enceladus has an effect on it’s aurora, a connection which will be the main focus of our project.
How do auroras on Saturn work?
Saturn’s aurora light shows are similar to those found on Earth in some ways, but they also differ quite a bit. These spectacular light shows are caused by an energetic solar wind that sweeps over the planet, much like it does on Earth.15 However, unlike on Earth, Saturn’s auroras can be seen only in ultraviolet light, and therefore are visible only from space using instruments sensitive to ultraviolet radiation.15 That is where the Cassini spacecraft became a very valuable tool for astronomers, which allowed them to view images of the auroras. The images reveal ripples and overall patterns that evolve slowly, appearing generally fixed in our view and independent of planet rotation.15 These variations indicate that the auroras are primarily shaped and powered by a tug-of-war between Saturn’s magnetic field and the flow of charged particles from the sun.15 On Saturn the auroras are approximately centered in between the combined poles.16 Astronomers discovered some subtle differences between the northern and southern auroras, which reveal important information about Saturn’s magnetic field.17 The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn’s magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south.17 Auroral displays are spurred when charged particles in space interact with a planet’s magnetosphere and stream into the upper atmosphere.18 Collisions with atoms and molecules produce flashes of radiant energy in the form of light.18 When Saturn’s auroras become brighter and thus more powerful, the ring of energy encircling the pole shrinks in diameter.18 At Saturn, unlike either of the other two planets, auroras become brighter on the day-night boundary of the planet which is also where magnetic storms increase in intensity.18 At certain times, Saturn’s auroral ring is more like a spiral, its ends not connected as the magnetic storm circles the pole.18 Hubble images show that auroras sometimes stay still as the planet rotates beneath, like on Earth, but also show that the auroras sometimes move along with Saturn as it spins on its axis, like on Jupiter.18 This difference suggests that Saturn’s auroras are driven in an unexpected manner by the Sun’s magnetic field and the solar wind, not by the direction of the solar wind’s magnetic field.18 In comparison to the auroras that people see on Earth, Saturn’s turn out to be quite different.
Saturn’s Auroras and The Moon Enceladus
With the recent finds from the Cassini space probe, scientists have found that the relationship between Saturn and its moon Enceladus is similar to the “electrical circuit” observed between Jupiter and three of its moons, specifically Io.19
How Does it Work?
Electrons move back and forth between Enceladus’s poles in various cycles, and the auroras are created when the electrons hit Saturn’s magnetic field. The process of creating the aurora is comparable to that which exists on Earth at high latitudes; the movements of fast-passed charged particles from the solar wind are bent by the Earth’s magnetic field and emit the lights we know as the Auroras.20 The fields formed by Jupiter and Saturn, envelop the orbits of the planets, and the process called electrodynamics coupling takes ions directly from the satellites, completing what is essentially an electrical circuit. The origin behind the aurora of Jupiter is thought to be sulfur from the volcanic activity of its moon Io, separated into electrons and ions by sunlight. However the alleged origin of electrons on Saturn’s moon Enceladus is “cryovolcanism”-volcanic activity that shoots up fluids and salty ice in the case of Enceladus.19 In comparison to Jupiter’s moon Io, the aurora footprint of Enceladus varies in brightness by about a factor of three.20 When observing Saturn there is no single substantial excretion of the plasma sheet at the location on Enceladus, but we see large variations in brightness. In contrast we know the emissions are caused by the “rocking of the magnetospheric plasma sheet as the magnetic dipole moment is inclined with respect to the spin axis.” 20 If we use that logic the variation observed on Saturn could reflect variations of Plume activity, which is the up welling of abnormally hot rock within a planet’s mantle or inner core. Therefore, the observed large scale variability is likely caused by cryovolcanism from Enceladus’ south polar vents, suggesting that plume activity was particularly high during August 2008.20
Click the following link to visually see the electric circuit:
The two images provided in the link above, were captured by Cassini’s ultraviolet imaging spectrograph on Aug. 26, 2008, separated by intervals of 80 minutes. It was observed that the auroral footprint change according to movement that aligned with the position of Enceladus. In this picture, the colors represent how bright the extreme ultraviolet emissions are. The lowest emission areas are in black/blue.21 The brightest emission areas are in yellow/white. In the brightest image the aurora footprint is observed with an ultraviolet light intensity of about 1.6 kilorayleighs which is comparable to the barely visible ultraviolet auroras observed on Earth without a telescope.21
How Saturn’s Aurorae differs from other planets
The Aurora’s on Earth are what we know the best. But in the constant observation and research done on the planets, we have discovered that there are Aurora’s not only on Earth, but on all the planets – aside from Mercury. In this section Saturn’s auroras are the main focus;
Saturn’s auroras can most easily be seen in ultraviolet light because Saturn’s atmosphere is more hydrogenic rather than oxygenic. The visibility of the auroras on Saturn depends on the solar winds and the rapid rotation of the planet. They last only about 11 hours.22 And the auroras can reach heights of more than 1,200 km. The main aurora on Saturn is caused by the solar wind, and the aurora changes dramatically as the wind varies. Saturn’s unique auroral features tell us there is something different about the planets magnetosphere and the way it interacts with other factors like the solar winds, the planet’s rotation, the atmosphere and the moons.
Saturn’s auroras are similar (but not the same) to the auroras of Jupiter, Uranus and Neptune (which are other gas giants) because they all have a main source of hydrogen, which makes them hardly visible to the human eye, if even visible at all. These lights are most easily seen with Ultraviolet light because of the hydrogen composition of them. The auroras on Saturn are very different from Earth because of the composition of them. Earth’s are visible because of the oxygen in the atmosphere, which is also why they glow green. Earths Auroras can range from 100km to 500km in height.23 The Aurora’s on Saturn are very different from Venus‘ auroras, because Venus doesn’t have a magnetic field that can play a role in the auroras, the auroras on Venus are sourced from a magnetotail which is carried by the solar winds from the Suns magnetic field.24 These auroras are only visible when the solar flares’ charged particles were directed directly at the planet. Excited oxygen atoms are assumed to be the cause of the flares of green light in Venus’ atmosphere.25 Again the auroras on Mars are very different from Saturn’s because while electrons typically cause auroras, Mars’ auroras are powered by protons. The sun ejects protons at speeds of up to two million miles per hour in the Solar winds. Observation showed astronomers that when the light would brighten in Mars’ atmosphere, there was an enhanced number of protons in the solar winds. There was trouble with this observation though because two questions remained – how did these protons get past the “bow shock” (a boundary where the solar wind is rapidly slowed so it can be diverted around the Martian space environment)? And how did Protons cause such a strong light, since atoms technically need electrons to do so? The protons did so by stealing the electrons from the hydrogen clouds surrounding the planet which transformed them into neutral atoms and this is how they got across the bow shock. When these high-speed atoms hit the atmosphere, they would give off ultraviolet light. The Auroras on Mars can happen anywhere in the atmosphere unlike Auroras on Earth or more importantly – Saturn. It is thought to be possible to view these lights from the surface of mars by the human eye because even though the atmosphere is primarily CO2, excited oxygen atoms in the atmosphere would cause green lights.26
Much of what we know about Saturn should be credited to the images we have obtained from the devices that were sent into orbit. It was determined that all planets in our solar system have auroras, with the exception of Mercury. Because the auroras were undetectable to the human eye for which visuals had to obtained via spectroscopy: detecting ultraviolet light. These images would give mankind there first look at how Saturn’s magnetosphere interacts with solar winds, atmosphere, physical properties,and Enceledes in particular.
It is determined that Saturn does have Auroras like other planets but the physical properties are distinct from the other planets. Once the images had been obtained it was determined that Saturn’s auroras had distinct features, like the other planets. Saturn’s auroras differed in size and quantity on both north and south poles. What was most interesting for this groups motivation in terms of research was the vast majority of moons the planet has surround and Enceladus in particular. Enceladus can be considered an active moon. It interacts with Saturn for the creation of the Auroras. Hence, the cryovolcanism on Enceladus causes electron discharge from the poles of the moon to the atmosphere of the planet then to the poles of the Saturn creating auroras.
It’s worth noting again that most of the planets in our solar system do have Auroras in the northern and southern poles. On Earth, auroras are visible because they reside in an oxygen atmosphere which gives a green like appearance in the sky. Saturn’s auroras appear invisible due to them being in a hydrogen rich atmosphere. The images and data collected from the spacecrafts that were sent into orbit should be fully credited for the information on Saturn and for what we know about Enceladus’ contribution on Saturn’s auroras and its functions.
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