The fractured terrain of Dione portrays the youngest geologic component.The names of many craters and cliffs are taken from locations and humans in the Aeneid of Virgil. There are many crater impacts on the surface of Dione.Dione is one of Saturn’s moons, the planet with the largest number of moons, 82 to be precise. After discovering the moon in 1684, Giovanni Cassini, an Italian astronomer, named the moon after Greek mythology, Titaness Dione. It is also referred to as Saturn IV. Cassini referred to the four moons of Saturn as Sidera Lodoicea, meaning the stars of Louis, honoring King Louis XIV, King of France. He found Dione using the huge aerial telescope he set up on the Paris Observatory grounds. The name Dione for this moon was suggested by John Herschel, son of William Herschel. Dione orbits the planet Saturn around a semimajor axis that is 2% less compared to the axis of the Earth’s moon. The orbital period of Dione is 1/10th that of the Earth’s moon. The current orbital resonance followed by Dione is 1:2 mean motion with the Enceladus moon. This means that for every two orbits of Enceladus around Saturn, Dione completes one orbit. The resonance supports the orbital eccentricity in Dione with tidal heating. It also maintains the eccentricity in the Enceladus’ orbit, supplying a heat source for the extensive geological activity in Enceladus. This activity mostly shows up as geyser-like, cryovolcanic jets.Dione CompositionThe likely composition of Dione is the combination of equal parts by mass of water ice and silicate rock.The moon Dione is small with a mean radius of about 349 mi (562 km). The density of Dione is 1.48 times the density of liquid water, which suggests that around one-third is composed of a dense core, likely of silicate rock and the rest of it is of ice. At an average temperature of -304 F (-186 C), the ice in Dione’s core is pretty hard, behaving a lot like a rocky core. The E-ring of Saturn creates a constant heavy bombardment of very fine ice powder that is similar to smoke on Dione. This dust in E-ring eventually comes from Enceladus that has notable geyser activity.Although made of water ice, Dione is believed to have less ice coverage around its rocky core compared to the moon Rhea.There may be a subsurface ocean hiding under the surface of Dione.As per the research done by Belgium’s Royal Astronomical Society, the presence of Dione’s gravity (Cassini data) could be due to 60 mi (100 km) of the ocean below the surface.The ocean underneath Dione’s surface would have formed when this moon formed 4 billion years ago.Along with the age of the moon and its core, the close contact of rock and water would make it a great mating ground for the life of microbes. This interaction provides an energy source and key ingredients, important contents for life.Dione is not the only moon of Saturn to have an ocean, the icy Enceladus and smoggy Titan also have oceans.As per the gravity and shape observations, the rocky core is around 248.5 mi (400 km) in radius and the surrounding water ice’s radius is 99.4 mi (160 km).The investigation of Dione’s internal structure was done by combining the moon’s topographical and gravitational analysis, exhibiting a larger deviation from the hydrostatic equilibrium that suggests a certain compensation degree.Dione’s FeaturesFeatures of Dione are - heavily cratered areas with craters measuring 62 mi (100 km) across, lightly cratered plains, moderately cratered plains, and regions of tectonic fractures.The heavily cratered areas on Dione’s surface are usually on the trailing hemisphere. Technically, a leading hemisphere of a moon must be more heavily cratered, and hence, a recent force spun Dione around. It is calculated that small bodies that can create 22 mi (35 km) craters on Dione’s surface could have spun this moon around its position. However, how this moon spun a complete 180 degrees is still a mystery.The heavily cratered terrain of Dione is identical to that one of Saturn’s other moons, Rhea, and it also has similar albedo features.The origin of the bright streaks or wispy streaks on Dione was unknown for so many years.NASA’s Cassini spacecraft was able to provide close-up observations of Dione’s surface, revealing that the wispy features were huge ice cliffs. NASA sent one Cassini flyby towards Dione.It is believed that the ice cliffs on this moon’s surface were formed by tectonic forces caused within the moon.The fractured terrain on the surface, seen through Voyager pictures, display thin, bright wispy lines that are lengthy and frequently cut through Dione’s craters and plains.This wispy terrain was shown by NASA’s Cassini spacecraft flybys as bright canyon ice walls, likely caused due to subsidence cracking.The lightly cratered plains were located on the leading hemisphere, while the heavily cratered plains were on the trailing hemisphere.The trailing hemisphere is very unique and has more dark material from the leading hemisphere on both Dione and Rhea.Dione has linear virgae that are evidently at lower latitudes and run parallel to the moon’s equator, which is also the feature recognized on the moon Rhea.The virgae are brighter than all the features around them and superimpose other characteristics like craters and ridges, meaning they are comparatively young.The origin of these lines has been proposed to be exogenic, due to the placement of the material along the surface by the material’s low-velocity impacts that are sourced from closely approaching comets, co-orbital moons, or Saturn’s rings.On December 13, 2004, the close-up images revealed the bright ice cliffs.Some geological features of Dione are classified as Dorsa (or ridges), Chasmata (canyons or chasms), craters, fossae (or long narrow depressions), and catenae (or crater chains).Dione Distance From EarthDione is at a distance of 234,500 mi (377,400 km) from our Earth.Giovanni Cassini discovered a wispy oxygen atmosphere around Dione. It is extremely thin and for every 0.67 cubic in (11 cubic cm), there is one oxygen ion. It is similar to conditions 250 mi (400 km) above our planet. Like several moons, including ours, Dione is a tidally locked satellite and the same side faces the parent planet. Dione is almost 11.3 times smaller than our Earth. Hence, our Earth’s mass surface area, radius, volume, and density are way higher than this icy moon.Voyager I was the first spacecraft to visit Dione in 1980. The trailing side’s wispy features were revealed by Voyager I.There are currently no missions towards the moon Dione, however, Dione’s surface nature, liquid water, and geological history make this moon suitable for future research.NASA scientists announced in 2013 that they received evidence through the Cassini spacecraft indicating that this moon of Saturn is way more active than they first realized.The difference in colors between trailing (more red and dark) and leading hemisphere (brighter) is because the leading side picks up material from the E-ring of Saturn that is fed by cryovolcanic emissions by Enceladus.The radiation from the magnetosphere of Saturn interacts with the trailing hemisphere of Dione, resulting in a darker and redder appearance of organic elements on the ice surface.Many astronomers believe that the moon Rhea may have been tidally locked with the planet Saturn in opposite orientation since most craters on Dione’s surface are situated on the trailing hemisphere.Dione is more spherical and has a thicker crust compared to its sister moon Enceladus.Dione is almost 20% the size of Ganymede, the largest moon in the Solar System.Dione (Moon) Orbital Period and AgeDione is orbiting around Saturn at 2.7 Earth days and its geologic age is around 4 billion years.In Greek Mythology, the name Dione is frequently described as Tethys and Oceanus’ daughter and resembles Gaia, the Earth Goddess. Dione consists of a trojan or two co-orbital with smaller moons of planet Saturn, Polydeuces, and Helene. They are situated within the Lagrangian points of Dione L5 and L5, that is 60 degrees beyond and ahead of Dione, respectively. In 1982, Stephen P. Synnot reported the leading co-orbital moon that was 12 degrees ahead of Helene. The geologic age of this moon was indicated by the distribution of sizes and density of impact craters.This interaction between other moons of Saturn and Dione influences the moons’ orbits.The eccentricity of the orbit of Dione is 0.0022.The history of cratering patterns and high albedo of the leading hemisphere shows that this moon has not changed its orientation for billions of years.Like Callisto or Jupiter IV, craters of Dione do not have high-relief features that are present on Mercury and Moon, which is likely due to the sagging of weakened ice crust over a period of time.Dione is Saturn’s fourth-largest moon. Dione also has interactions with Saturn’s larger moons, Enceladus and Mimas.The instruments within the unmanned Cassini probe that flew across the Dione moon on April 7, 2021, observed a slim layer of oxygen ions present around the moon.The molecular oxygen ion layer was so thin that astronomers considered it an exosphere instead of a tenuous atmosphere.The instruments in the Cassini could not determine the presence of water in the oxygen ion layer because of high background levels. However, it looks like the highly charged particles from powerful radiation belts of the planet are able to split the water within the ice into oxygen and hydrogen.Like our planet’s moon, Dione is also phase-locked with its parent planet Saturn and one side of the moon’s surface always faces Saturn.
The fractured terrain of Dione portrays the youngest geologic component.
