The Saturnian Moon of Enceladus has an impact on many of the other moons of Saturn as its geysers spew water ice, and ice particles, which cover the surfaces of other neighboring moon. The Dione moon is one such moon affected by the icy ejection from Enceladus.
Saturn’s Moons and Rings:
Saturn is the second largest Planet in our solar system, after Jupiter, and the 6th furthest from the Sun.
It is probably mostly recognized as the large Red Planet with rings – Saturn’s Rings. There are 14 sub-divisions of its rings with the widest ring, the B ring, measuring 25,500 km.
There is not just one moon of Saturn, it has a total of 62 moons in orbit around it and most are fairly small with a low density. Of the 62 moons orbiting Saturn and of those 53 are named and of those 24 are regular satellites with a prograde orbit.
The 24 regular satellites include the 7 major moons, another 4 smaller moons that exist in a Trojan orbit with the bigger moons, 2 co-orbital moons that guard Saturn’s F Ring. The others are located around the other Rings such as the G Ring between Mimas and Enceladus and E-Ring where the Dione Moon is located.
The 7 major moons closest to Saturn are:
FACT: Many Space objects have been named after the Titans but just who were the Titans? In Greek Mythology the Titans were the race of immortals that ruled the universe, before the rise of Olympians, with Cronus as King, and Rhea as Queen. Cronus (or Kronus) was the father of Zeus.
Let’s take a look at Saturn’s Moon Dione
Saturn’s Moon Dione is an icy moon and one of the many Planets and Moons named after a Giant from Greek Mythology or Roman Mythology. Dione is a mid-sized moon and ranks as the 4th largest of the 7 major Saturnian moons, and is around 20% of the size of Titan (the largest of the seven)
It is the 15th largest moon overall in the Solar System, with a diameter of 697 miles (1,122Km), and at this size it is more massive than the combined size of all the other known moons that are smaller that it.
Who discovered Dione and the other icy moons of Saturn?
The Moon Dione, Saturn IV, was one of the 4 moons of Saturn discovered in 1684 by the Italian-French mathematician and astronomer Giovanni Cassini:
- Dione, Rhea, Iapetus and Tethys
Giovanni Cassini also compiled solar tables and data about the moons of Jupiter and used those calculations to more accurately measure the circumference of Planet Earth. He also attempted to measure the size of the Solar System by comparing distances between Mars and Earth.
In 1669, King Louis XIV of France appointed Cassini as Director of The Paris Observatory and to serve as his court astronomer/astrologer.
Cassini continued to balance his interest in mathematics and astronomy and in 1684 he discovered a pair of moons orbiting Saturn – they were named Iapetus and Rhea. He then discovered another 2 moons of Saturn and called them Tethys and Dione in honor of the Titans.
He collectively named these 4 moons ‘Sidera Lodoicea’, meaning the ‘Stars of Louis’, in recognition of his King and employer, King Louis XIV of France.
Neighboring ice moons Mimas and Enceladus were discovered by William Herschel in 1789, and his son John Herschel continued his good work.
It was John Herschel, in 1847, who suggested the Moons of Saturn should be named after Titans, or family of Cronus from Greek mythology (known as Saturn in Roman Mythology).
It was NASA’s Cassini spacecraft mission that brought us images in graphic detail of these moons from its close flybys of these ice moons in 2005
Dione has a low density, suggests it is composed of water ice like its neighboring moons, Rhea and Tethys, however Dione has a higher density than Rhea (which is the largest inner moon but geologically dead), but has a lower density than Enceladus.
How were these inner moons of Saturn discovered?
Saturn’s moon Dione, also known as Saturn IV, and the other inner moons of Saturn have been observed and photographed in detail over the years by NASA spacecraftflybys missions by ‘Voyager’, (Voyager 1, Voyager 2), and NASA’s Cassini spacecraft.
FACT: E.E. Barnard discovered the very first inner moon/satellite in 1892. It orbits the Planet Jupiter and is called Amalthea.
In 1966 the Saturnian moons – Janus and Epimetheus – were first observed. They are interesting as they share the same orbit, which initially caused come confusion. Could there really be two moons in the same field?
We are grateful to NASA for its variety of inner moon images, which helped clarify the positions and movement of these Saturnian moons.
NASA’s Cassini Spacecraft has brought us close up images of moon surfaces created by possible tectonic and liquid water eruption activity, forming unusual water ice surfaces that sometimes hide a very different composition ranging from a rocky core to global oceans.
Future missions by NASA and Planetary Science institutes
Future NASA missions and planetary science research over the next 20 years is likely to target the Ocean Worlds of the Solar System.
This could be through a combination of robotic missions and laboratory simulation attempting to investigate and even sample the complex organics, surface features, and cratering of the ocean world.
What did they discover close up on Dione?
Dione’s surface is an intriguing moon to study, as it has a mix of terrain. It displays fairly old heavily cratered terrain with an extensive network of lineaments and troughs.
The indents and fracturing, causing ice cliffs, on the surface of Dione are more prominent in the trailing hemisphere than in the leading hemisphere.
There is much evidence of fractures on Dione’s surface in the trailing hemisphere, in fact there are several intersecting sets of fractures and they are described as ‘Wispy Terrain”. This unusual cratering suggests that the Moon Dione had some sort of previous global tectonic activity. The lasting result was a collection of tectonic fractures, fault lines and cratering markings on the surface of this moon.
Dione has an atmosphere composed of oxygen ions. Bodies like the Space Science Institute (SSI) and the Planetary Science Institute (PSI) in the meantime will attempt to simulate activity on and beneath the surface of these moons.
Plenty Of Targets
Several moons are popular for further investigation, especially Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, especially as it is thought that life could exist in a warm liquid water interior ocean.
The success of these NASA space missions requires years of planning and research before launch. A recent study in the Icarus scientific journal addressed the composition of planetary surface features and how through simulation based on remote photo polar metric observations, it can appear real before it happens.
The study’s lead author, Robert M. Nelson is a senior scientist the Planetary Science Institute (PSI) and scientists from JPI and Caltech were a co-author of the study. The success of these missions may be affected by the very low-density surfaces, which warns that these icy surfaces may be too soft to land on.
Cassini spacecraft research missions
As some of the inner moons of Saturn are not visible by naked eye we rely on observations from various Nasa spacecraft missions for details.
The close proximity of Dione to Saturn and its rings makes it difficult to spot from Earth, even though it is a bright object in the Solar System.
It was Pioneer 11 that carried out the first flyby of Saturn in 1979 and then Voyager completed another flyby. This provided further detailed photos of the Planet Saturn’s orbiters such as Saturn’s Moon Dione.
NASA has been instrumental in completing several successful missions into Space to observe the Planet Saturn, Saturn’s rings and Saturn’s moons.
Images have been captured and shared by the Cassini Spacecraft missions, JPL and the Space Science Institute (SSI)
FACT: NASA aims to explore, discover and expand our knowledge for the benefit of mankind. As well as facilitating spacecraft missions, via Voyager 1 and Voyager 2 and the Cassini Spacecraft missions, it also has a National Laboratory in Space.
Cassini last passed the Moon Dione at a close up distance of 295 miles (474 km) in 2015 and captured some fairly detailed images, through JPL, of this icy pockmarked surface. In 2011 it passed even closer to Dione at a distance of 60 miles (100 km).
What does this Saturn Moon Dione look like?
The Surface Features of Dione
Saturn’s Moon Dione is a small icy moon. Its surface is constantly being bombarded with fine ice powder from Saturn’s E-Ring. This dust originates from the geysers, on the Saturnian Moon Enceladus, that spew water ice out at speed and the ice particles cover several other Saturnian Moons. There is no geological activity on Dione.
FACT: Geological activity is the movement of tectonic plates beneath the surface of a Planet or Moon. For geological activity to occur an energy source, namely heat is required. It is the heat that causes the tectonic plates to shift.
The driving force behind the geological activity on a moon is still somewhat unclear, other than it certainly involves a heat source. Dione is one of Saturn’s icy moons, with a mixed and cratered terrain surface containing several impact craters, some are as big as 250km in diameter.
Unusually, the trailing hemisphere in Dione is more heavily cratered than the leading hemisphere, and has an intersection of fractured areas known as the Wispy Terrain, or wisps.
An alternative theory on the cratering on Dione
Two Scientists, Shoemaker and Wolfe had a different opinion and suggested a cratering model for a tidally locked moon (in the opposite direction), with its greatest amount of craters on the leading hemisphere and much less on the trailing hemisphere.
It is ice cliffs that form the wispy terrain
The Dione moon also has some smoother areas on its surface with low impact cratering that suggests this area may have been resurfaced at some point in the past due to tectonic activity.
Brightness and Color – the Albedo Scale
FACT: Albedo is the measure of the diffuse reflection of solar radiation, out of the total solar radiation. The Albedo scale in visible light ranges from:
- 0 – a low albedo representing a black colored object like charcoal
- 1 – a high albedo representing a white colored object like snow or ice particles
Ocean surfaces and forests have low albedo, whereas an area of desert has a high albedo.
The Dione Moon is uniformly bright with a visual albedo of 0.998
Cratering and Fissures
The surface of Dione has several different types of terrain:
- Wispy areas on the trailing side, which are actually ice cliffs
- Shiny ice in a Criss-cross pattern, formed from darker material falling off the ice cliffs
- A very thin wispy oxygen atmosphere, equivalent to oxygen found around 300 miles above
How does a Moon get its name?
Giovanni Domenico Cassini discovered and named the icy moon Dione. This moon like many other inner moons of Saturn was named after a Titaness from Greek Mythology.
The name Dione means goddess and there are 4 characters named Dione from Greek Mythology, and aptly one is the daughter of Oceanus and Tethys (the name of a neighboring moon of Saturn)
It was Giovanni Domenico Cassini, in 1675, who discovered that ‘the Ring of Saturn’ was not one single ring, but rather it was several smaller rings.
The rings are named from A to G, in the order in which they were discovered and are not solid rings but are composed of ice particles and water ice, with gaps in between them. The distance between the gaps is not equal in each ring they vary considerably.
The closest ring to Planet Saturn is the D Ring, then C Ring,B Ring, followed by A Ring and then F Ring, and finally the two fainter Rings G and E Ring. Saturn’s E Ring is the outermost ring of the major rings.
The Moon Dione orbits within the densest area of Saturn’s E Ring, close to neighboring moons Tethys and Enceladus.
The Cassini Division
The largest gap between the rings is the gap between the ‘B ring’ and the ‘A ring’, with a distance of approximately 4,800 km in between them. This gap is known as the ‘Cassini Division’.
Physical Characteristics of the Dione Moon
Position in Space
Dione is the 4th largest moon that orbits the Planet Saturn
Saturn IV ‘s orbital distance from Saturn is 234,500 miles (377,400 km). This is roughly the same distance from Planet Earth to its only moon.
The moon Dione has a mass of around two thirds water ice and its densest part is its rocky core, which is likely to be composed of silicate rock. It has large ice cliffs formed by fractures in the ice and many ice craters on the surface too.
The icy surface of Dione is similar to Tethys has a temperature of around -187 degrees Centigrade (-307 degrees Fahrenheit).
This image of the reflective and bright surface of this icy moon Dione has been captured many times by NASAs Cassini Spacecraft, and reported back to their scientists at the Southwest research Institute (SwRI).
Like many of its neighboring moons of Saturn it is also bombarded by ice particles spewing forcefully and travelling in their direction from the geysers on the icy active moon Enceladus.
The Dione Moon is 3rd largest of the inner moons orbiting Saturn and the 15th largest in the whole Solar System with a radius of 348.8 miles (561.4km)
Dione is a very bright and reflective moon as its surface is primarily covered in water ice and this becomes reflective when sunlight makes contact. Most of the larger moons (also known as satellites) of Saturn keep one side facing Saturn as they rotate within their orbital period.
The average orbit distance from Dione to the center of Saturn is around 200,000km. The orbital period takes the equivalent of 2.7 Earth days (64.8 hours approximately to orbit once round Saturn)
FACT: The orbital inclination of a moon is the angle at which it orbits its parent planet in relation to the orbital plane.
The orbital inclination of Dione is about 0.02 degrees. Like many other Moons, it is tidally locked which means the same side always faces its parent planet.
Dione has two co-orbital moons, also referred to as Trojan moons, they are called Helene and Polydeuces and orbit close to the Lagrange Points (or lagrangian Points) of Dione.
The Lagrange points for Helene and Polydeuces orbit are L4 and L5, or 60 degrees ahead and 60 degrees behind Dione.
FACT: The Langrangian Points are special places in the Universe where the forces of gravity are balanced. They are sometimes also referred to as the liberation points or L-Points.
FACT: Eccentricity is the measure of the deviation of the Earth’s orbit from a circular object, using the scale where 0 is a circular orbit, anything from 0 to1, is elliptical to highly elliptical orbit (HEO), and 1 and over is parabolic.
For Dione its orbital eccentricity of orbit is 0.0022, which means it has a close to circular type prograde orbit around Saturn. This is the round shape we usually associate with a Moon.
Dione has an equatorial circumference of 3529 km.
The Dione moon is about one third of the size of Planet Earth, and is the 15th largest moon in the Solar System. Dione is one of the better known inner moons of Saturn and with a diameter of around 697 miles (1122 kilometers).
Many of our images showing the detail of the surface, shape and possible density of Dione is thanks to the efforts of the NASA Cassini spacecraft, travelling quite close to Dione on its 2005 flyby mission.
This is an icy moon, that’s associated with wispy terrain and mysterious cratering patterns.
The surface of Dione looks like it has been cracked and pitted. The surface is mainly covered with fresh ice particles, which makes it highly reflective due to light bouncing off it.
Dione is one of the brightest of all of the Saturnian moons as it reflects the Sun’s light. The appearance of this moon when captured by NASA looks like it has craters, huge ice cliffs, large canyons and ridges. It is believed that these large bright ice cliffs were not formed by early cryovolcanoes activity.
NASA’s Cassini-Huygens spacecraft during its flybys in 2005 has captured the best ever detailed images of many different moons during the same mission. It captured the incredible wispy terrain of Dione in a flyby approach this to within an altitude distance of 500 km, above the surface of this satellite (moon).
Dione was confirmed as the third largest icy moon after Iapetus and Rhea. The surface of Dione and other Saturnian moons is a mix of ice and impurities, although some display a hint of color. The Cassini-Huygens spacecraft mission confirmed streaked terrain, supporting the earlier sighting of inter-connected tectonic fractures on Dione’s trailing hemisphere.
This moon has a low density measuring a density of 1.476g/centimeters cubed (1.48 times that of water, and water which is 1gm/cm3) meaning it is almost completely composed of water ice with a dense core. If it were located closer to the Sun it would melt.
Observations of the surface of Dione show areas that are heavily occupied by impact craters. The cratering distribution, and sizes, and density suggest a geologic age of around 4 billion years.
Dione remains as a circular shape and has a normal prograde orbiting behavior
Notable Features of Dione Moon
Dione is an icy moon with a wispy surface and has one of the brightest surfaces of all bodies in the Solar System. It is the fourth furthest large moon from the Planet Saturn.
Perhaps its most notable feature is its large impact cratering and bright streaks
Dione orbits Saturn within the densest part of the E Ring, the outermost of Saturn’s rings in a prograde/direct motion direction following in the direction of the rotation of Saturn.
It orbits at a distance of 234,500 miles (377,400 km) from the center of Saturn, at an average speed of 36100.40 km/h.
This orbit of Saturn takes around 64.8 hours and during this time it is facing the direction of its parent Planet the whole time. The orbit position is described as being tidally locked to the Planet.
The escape velocity
The escape velocity of a space object is the speed it needs to be travelling at in order to break away from the gravity of its main object (for example Saturn).
Basically the larger the object the faster it has to travel to break free. For Dione, the escape velocity is 0.51 km/hr.
Orbital resonance occurs when orbiting astronomical bodies (usually a pair) bring regular, periodic gravitational influence to each other.
The mass of Dione is estimated at 1,095,745,430,185,280,000.000 kg, less than 1% of Planet Earth
It is believed that around 2/3 of Dione is water ice, and it also has a rocky core. It is not certain if Dione has an ocean beneath its surface, but it is assumed. Dione is so cold that its ice is as hard as rock.
Dione is estimated to be a few billion years old, up to 4.5 billion years of age, possible as old as the moon of Planet Earth.
The Geography of this Moon
The Moons of Saturn are grouped according to their proximity to Saturn, their orbit and size. This moon is unusual as it has an icy surface covered in a terrain of wisps, ice cliffs and craters, of all shapes and sized and not uniform at all.
It is bright reflecting sunlight on its icy surface. It thought to have different types of terrain:
- Densely cratered old terrain, lightly cratered plains, and areas of tectonic features, troughs and lineaments suggesting previous global tectonic activity
It is the largest innermost moon to Saturn.
Dione has huge craters on the surface, some are estimated to be around 62 miles wide (100km). The surface features for Dione are fascinating for scientists as the more craters are found on the trailing hemisphere (backside of this moon) than the leading hemisphere (front side of this moon.
The opposite is normal for moons and the front side/leading hemisphere would normally storm through space debris and take the impact of travelling objects.
The only explanation is that perhaps during some impact on this moon Dione was spun around. However for it to be spun around exactly 180 degrees poses a mystery!
Observations – what’s close, what’s passing by, what’s changing?
The Moons of Saturn are all quite different, in size and shape depending on their own gravity. Dione is tidally locked with its parent Planet Saturn and therefore the same side always faces Saturn during orbit.
- Saturn is sometimes referred to as ‘The Jewel of the Solar System’.
- The low temperature at the point where Saturn is in the Solar nebula suggests that water ice was the main solid component from which all these moon were formed.
- It is believed that Saturn and Jupiter are relatives, as they are very similar in their atmospheric composition
- Planetary Science is fascinated in the idea of finding alien life on another planet or moon. So where there is a confirmed water source and atmosphere we are particularly interested in any investigations
- Saturn has a number of moons not yet officially confirmed as moons.
- Earth passes through the Saturn ring plane approximately every 13 to 15 years
- The Dione moon is only around 1/3 of the size of Planet Earth
- The name Dione is also made famous by the novelist Homer in his book “The Iliad’”
- Saturn has 56 confirmed Moons and many more not yet confirmed as Moons. For this reason Saturn is sometimes referred to as the ‘Moon King”
- The JPL imaging operations center is based at SSI (the Space Science Institute) in Colorado, USA
- The Cassini-Huygens Mission is a joint collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ISA)
- NASA’s Cassini spacecraft was in the Saturnian system from 2004 to 2017
- The naming of Astronomical Bodies is now strictly controlled by the International Astronomical Union (IAU)
- Dione Moon: By NASA – Public Domain, https://commons.wikimedia.org/w/index.php?curid=92817828
- cassini space craft: By NASA/JPL – Public Domain, https://commons.wikimedia.org/w/index.php?curid=626636
- Dione Surface: By NASA/JPL-Caltech/Space Science Institute – Public Domain, https://commons.wikimedia.org/w/index.php?curid=42637809
- saturns ring: By NASA / JPL-Caltech / Space Science Institute – Public Domain, https://commons.wikimedia.org/w/index.php?curid=29592312
- cassini division: https://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/cassini_division.html
- giovanni domenico cassini: Public Domain, https://commons.wikimedia.org/w/index.php?curid=44215
- Four Giants: https://www.worldatlas.com/r/w960-q80/upload/30/a0/3b/shutterstock-1029243295.jpg