The Enceladus moon is one of the more interesting and promising companions to Saturn. It is known as an inner moon, and it is here that we will start this guide.
What is an inner Moon?
An inner moon is also referred to as an inner natural satellite.
When astronomical bodies such as moons and satellites orbit a planet they do so in one of two directions, known as:
- Prograde/direct motion – is an orbit in the same direction as the rotation of the primary object
- Retrograde motion – is an orbit in the opposite direction as the rotation of the primary or central object
An inner moon, or inner natural satellite, follows a prograde low inclination orbit, inwards of the outer and larger satellites orbiting the parent body.
These inner satellites/moons differ from other satellites as they are located closer to their parent astronomical body. They are usually smaller with a low density, and take a shorter time to orbit their Planet than regular satellites.
The Four Giant Planets
Each giant Planet has inner moons orbiting them.
There are 30 inner moons/satellites currently identified with these 4 Planets. They were formed at the same time as their Planet.
They are small and difficult to see by naked eye from Earth as they suffer from glare from their Planet.
The inner moons of Saturn have been observed by the NASA Cassini mission and discovered that they are constantly having small particles from Saturn’s rings falling onto them, ranging from ice particles to ice grains.
The inner moons are all different differing in size, characteristics and shape. Their organic molecules content determines their color.
Generally the innermost moons contain iron and red organic molecules and material are redder in color that the outer ones.
The outermost ‘inner icy moons’, are blue in color because they have an icy crust and icy surface due to the ice and water vapor from the liquid plumes that come out of the Enceladus Moon itself.
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, only 7 are major moons.
The 7 major moons of Saturn are:
Let’s take a look at Saturn’s Moon Enceladus
Saturn’s Moon Enceladus, also the name of a Giant from Greek Mythology, is the 6th largest Moon of the 7 major moons of Saturn, although it is considered a small moon and is only around 10% of the size of Titan (the largest of the seven)
Enceladus was one of the moons of Saturn discovered in 1789 by the German-born English Astronomer William Herschel using a 40 foot reflector telescope. Following his death in 1822, his son John Herschel continued his observations and astronomical work.
Frank Postberg, and his colleagues from the University of Heidelberg in Germany have continued to examine the dramatic features of Saturn’s moon Enceladus, since NASA’s Cassini spacecraft mission shared its images from its close flyby in 2005.
Postberg interprets the plume sprays of water ice and water vapor that eject from the hydrothermal vents on the south polar region of this moon. He identified large fragments of complex organic molecules in the ejected ice. These hydrothermal vents on the moon are similar to the hydrothermal sites situated on the bottom of Earth’s global ocean.
FACT: Enceladus moon has a massive subsurface ocean. Its hydrothermal vents blend material from the porous core and water from this subsurface ocean and eject it into Space as water vapor and ice grains.
The combination of complex organic molecules, hydrothermal activity and liquid water could be a cocktail that could support life on a moon.
How were the inner moons of Saturn discovered?
Saturn’s moon Enceladus and the other moons of Saturn have been observed and photographed in detail over the years by NASA spacecraftflybys 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.
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 simulations attempting to investigate and even sample the complex organics and hydrothermal activity of the ocean world.
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.
The most likely candidates for further investigation are Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, especially as it is thought that life could exist in a warm water interior ocean like the Enceladus Ocean.
The success of these space missions requires years of planning and research before launch. A recent study in the Icarus scientific journal addressed the composition of these planetary surfaces 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
Could Enceladus support life forms?
The NASA Cassini spacecraft scientific research institute, at the South West Research Institute (SwRI), is based in San Antonio, California. It has been developing geochemical models to investigate evidence of complex organic molecules in Enceladus.
The South West Research Institute geochemical model has discovered carbon dioxide (CO2), in Enceladus may be controlled by chemical reactions on its seafloor.
The modeling of chemical processes within the subsurface ocean in Enceladus indicates the possibility that a diversity of microbes could possibly be supported in these conditions.
During the Cassini mission ending in 2017, samples of the plume of ice grains and water vapor from the geysers on the icy surface of the moon of Enceladus were captured. In a scientific paper published in the Icarus scientific journal, by Christine Ray, lead author investigated other energy sources via the Cassini mission
The plume samples revealed molecular hydrogen, meaning there is free energy in the Enceladus Ocean, which could be a food source for microbes.
On Earth there are 2 types of microbes:
- Aerobic (oxygen breathing) – consume energy in organic matter, oxygen and glucose, and produces carbon dioxide and water
- Anaerobic – metabolize hydrogen producing methane. Hydrogen is a source of chemical energy enabling the anaerobic microbes to survive in the Earth’s oceans near hydrothermal vents on the seafloor
FACT: Hydrothermal vents occur when seawater drips down through fissures in the ocean crust, near tectonic plates. The seawater is heated with volcano magma, resurfacing to form these vents.
There is evidence of hydrothermal vents on the moon Enceladus, and chemical reactions associated with the chemical disequilibrium between reductant and oxidant compounds in the ocean and rocky core. These conditions could support life and hydrothermal activity.
What does this Saturn Moon look like?
As some of the inner moons of Saturn are not visible by naked eye we rely on observations from various Nasa missions for details. The close proximity of Enceladus to Saturn and its rings makes it difficult to spot from Earth, even though it is one of the brightest 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 and Saturn’s Moon Enceladus.
NASA has been instrumental in completing several successful missions into Space to observe the Planet Saturn, Saturn’s rings and Saturn’s moons.
FACT: NASA aims to explore, discover and expand our knowledge for the benefit of mankind. As well as facilitating spacecraft missions, via Voyager and the Cassini mission Spacecraft, it also has a National Laboratory in Space.
Saturn’s Moon Enceladus is a spherical icy moon and when it rotates gravity causes an equator bulge.
Enceladus is a spherical icy moon with a variety of markings on its surface.
- Northern latitudes have heavily cratered markings
- Middle and Southern latitudes have wrinkles and fracture markings, and the Southern polar region is active
How does a Moon get its name?
It is believed that John Herschel, son of the discoverer, astronomer William Herschel named the first 7 Moons of Saturn after mythological figures associated with the Roman Titian of time, Saturn.
Saturn is named as Cronus, the leader of the Titans and the youngest of the first generation of Titans in Greek Mythology.
He gave this inner moon of Saturn the name ‘Enceladus’.
Enceladus is named after the son of Uranus and Earth (Gaia) from Greek Mythology.
The other regular satellites (moons) associated with Saturn are also traditionally named after the characters in the Titan generation or other characters associated with 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 have 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 C Ring, then B Ring, followed by A Ring. The Saturn’s E Ring is the outermost ring of the major rings.
The Moon Enceladus orbits within the densest area of Saturn’s E Ring.
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 kilometers in between them.
This gap is known as the ‘Cassini Division’.
Physical Characteristics of the Enceladus Moon
A cross section of the moon Enceladus would show a rocky core in the center, then a global ocean and an ice crust on the surface
The icy surface of Enceladus has a temperature of around -198 degrees Centigrade (-324 degrees Fahrenheit), with an icy crust.
This image of the reflective surface of this ice shell of Enceladus has been captured many times by NASAs Cassini Spacecraft, and reported back to their scientists at the Southwest research Institute (SwRI).
Enceladus is sometimes referred to as being an icy world, as is the moon Europa.
The Enceladus Moon is 6th largest of the moons orbiting Saturn and has a radius of 155 miles (252km)
Enceladus is a very bright 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. In the case of Enceladus this is its south polar region.
The average orbit distance from Enceladus to the center of Saturn is 238,000km, and its orbital period takes the equivalent of 1.37 – 1.9 Earth days (32.9 hours approximately to orbit round Saturn)
At this speed it is possible to witness its movement over the course of one night of observation.
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 is parabolic.
For Enceladus its eccentricity of orbit is 0.0047, meaning it is closer to an elliptical orbit.
This is more of a distorted oval shape than the round shape we usually associate with a Moon.
This shape and form of Enceladus is caused by the pull and compression of Saturn’s gravity. This creates heat in the interior of this moon and as a result facilitates geological activity on its icy surface area. Enceladus has a surface gravity of 0.113, and the Planet Earth has a surface gravity of 1.
As it orbits Saturn it creates a spray of ice particles, which form a circle around Saturn known as Saturn’s E Ring.
Enceladus has a surface area of 789,648.27 square kilometers with an Equatorial circumference of Enceladus is 1584 km.
Enceladus is one of the better known inner moons of Saturn and with a diameter of around 310 miles (500 kilometers).
Enceladus Moon is only around 10% of the size of Planet Saturn’s biggest Moon, Titan, and around 1/7 of the diameter of Earth’s Moon.
Many of our images showing the detail of the surface, shape and possible density of Enceladus is thanks to the efforts of the NASA Cassini spacecraft, travelling quite close to Enceladus on its 2005 flyby mission
This is an icy moon, that’s shiny and patterned.
The surface of Enceladus looks like it has been painted giving it a reflective ice shell appearance. The surface is mainly covered with fresh ice particles, which makes it highly reflective due to light bouncing off it.
Enceladus is the most reflective of all of the Saturnian moons as it reflects about 99% of the Sun’s light (even the bright Planet Venus only reflects 65% of the Sun’s light). The appearance of this moon as captured by NASA looks like it has tiger stripe indents on one side and older formed craters on the other side. It is estimated that this ice crust could be as deep as 12 – 15 miles.
Enceladus is known for spewing fountains of water ice out of its surface, from cryovolcanoes near the South Pole We now know that surface of Enceladus is geologically active.
Gravity & Geological Activity
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.
It is thanks to the gravitational pull of Saturn that Enceladus has incredibly hot geysers regularly spewing liquid water, and water ice, thousands of km out of the surface. These ice particles spew from active fissures that resemble the pattern of tiger stripes and are seen on the south pole of Enceladus. The plumes contain salt, which suggests that this water may have a liquid water ocean source under its icy crust.
It is not certain if this Enceladus Ocean is a subsurface ocean or a deep liquid ocean with an actual ocean floor or sea floor. Ice and liquid water are ingredients required to support alien life forms, so who knows! The driving force behind the geological activity is still somewhat unclear, other than it certainly involves a heat source.
NASA’s Cassini-Huygens spacecraft during its flybys in 2005 has captured detailed images of Enceladus. This flyby approached this moon to within a distance of 170 km. The spewing hot geysers of Enceladus are one of its most popular features of this white icy moon. These geysers can be observed spewing liquid water and dust and are at their most active when Enceladus is at its furthest point from Saturn.
The surface of Enceladus and other Saturnian moons is a mix of ice and impurities.
This moon has a density of 161 g/ centimeters cubed
Enceladus remains as a spherical shape due to its gravity and is the smaller object in our solar system existing under such gravitational formation.
Most of the features of Enceladus are typical of tectonic activity such as geological activity within this moon. The different terrains of Enceladus include fractures, grooves ,deep canyons and steep cliffs
Notable Features of the Enceladus Moon
Enceladus is an icy moon and has the whitest and most reflective surface of all bodies in the Solar System.
Perhaps its most notable feature is its tiger stripe markings on the South Pole side
The Cassini spacecraft made an unusual discovery in its 2010 mission without an explanation. It appears that Mimas has a thermal anomaly where the regions that are heated by the Sun actually have the coldest surface temperatures.
Enceladus orbits Saturn within the densest part of the E Ring, the outermost of Saturn’s rings in a prograde/direct motion direction following in thedirection of the rotation of Saturn. It orbits at a distance of 147,886miles (238,000 kilometers) from the center of Saturn.
This orbit of Saturn takes less than 24 hours and during this time it is facing the direction of the Sun the whole time. This 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 Enceladus, the escape velocity is 861km/hour.
Orbital resonance occurs when orbiting astronomical bodies (usually a pair) bring regular, periodic gravitational influence to each other.
The mass of Enceladus is higher than first imagines it is now estimated at 107,944,591,230,692,000,000 kg. It has a mass of around 680 times less than Earth’s Moon It is believed that Enceladus has a rock fraction of over 50% making it the most Silicate-rich object in the Solar System.
Enceladus is estimated to be around 5 billion years of age.
The Geography of this Moon
This moon is unusual as it is almost entirely composed of ice, its covered in craters and fractured terrains, of all shapes and sized and not uniform at all. It is bright reflecting sunlight on its icy surface. It thought to have five different types of terrain:
- Cratered terrain, ridged terrain, young smooth terrain, linear cracks and scarps were
It is the innermost moon of Saturn.
Enceladus has a slight wobble as it orbits Saturn, this waver occurs in most other moons. This perceived movement (an oscillation in its orbit) when viewed from Earth is known as the Moon Liberation.
The moon liberation effect changes our perspective when we look at the moon and it appears to change its shape before our eyes.
This liberation leaves scientists thinking that the inner part of Enceladus is not uniform. It is therefore indicates that Enceladus a has liquid ocean, and a rocky core.
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.
Saturn’s main ring system is linked with a group of small moons – Pan and Daphne orbit within the A Ring, and Pandora and Prometheus, orbit just outside the F Ring.
- Saturn is sometimes referred to as ‘The Jewel of the Solar System’.
- 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 is the least dense and flattest planet in the Solar System
- Earth passes through the Saturn ring plane approximately every 13 to 15 years
- The Enceladus moon is only around one seventh of the size of Planet Earth
- Enceladus is said to have a pattern like tiger stripes on its south pole surface
- Saturn has 56 confirmed Moons and the other 3 Moons, often associated with Saturn,are not yet confirmed as Moons, and for this reason Saturn is sometimes referred to as the ‘Moon King”
- The Planet Saturn is tilted
- 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 the first flyby mission to study Enceladus in detail
- Bubbles of gas rise up through the Enceladus Ocean to the surface, which could transport organic material from the depths.
- cassini space craft: By NASA/JPL – Public Domain, https://commons.wikimedia.org/w/index.php?curid=626636
- 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
- saturn’s moon enceladus: Public Domain, https://commons.wikimedia.org/w/index.php?curid=44644158
- Athena and enceladus: By Oltos? (Louvre), circle of Psiax (Mertens) – Marie-Lan Nguyen (2007). https://commons.wikimedia.org/w/index.php?curid=2707926