Enceladus Research Paper

Enceladus, the sixth largest of more than 62 moons that orbit Saturn, however of the 62 Enceladus is one of the most prominent and most varied moons to cycle the planet. Unlike most moons Enceladus is a very bright body, reflecting almost 100 percent of the light that that strikes its surface (making it one of the brightest objects in the solar system). With that being said, it still cannot be seen with the naked eye and must be viewed from a rather large telescope. This is due to the fact that it is small in comparison to the planet itself and that it can easily be outshined by the rings it resides in.
Enceladus was first observed by William Herschel on August 28, 1789 when turned his 1.2 meter telescope to the ringed planet Saturn. Herschel managed to avoid a large amount of the glare from the rings and get a much clearer view of Enceladus by observing it during Saturn’s equinox (Redd, 2013. "Enceladus: Saturns Tiny, Shiny Moon "). Herschel initially named the moon “Saturn II” which stuck with it until 1847 when William Herschel’s son, John Herschel, published a report which suggested that the moons be named after the various titans from Greek mythology (seeing as they were orbiting Saturn or Cronus and the children of Cronus where the titans in Greek myth) (Blunck, Solar system moons discovery and mythology, 2010). According to Greek mythology Enceladus was the primary adversary of Athena in the battle between the titans and the gods and at some point in the great battle Athena had injured Enceladus, thus causing him to flee the battle. However Athena threw the island of Sicily at Enceladus, thus burying him alive. It was thought afterwards that the earthquakes and volcanic eruptions on the island where caused by the titan rolling in pain under the mountain and that the volcanic material spewing out was from the titans breath ("Enceladus" greekmythology.com). We will see later why this name was coincidentally ideal for this moon in particular.
After Herschel’s initial discovery, the moon itself was not revisited/studied until almost 193 years later. September 1st 1979 we got a slight glimpse of the moon with the aid of the pioneer spacecraft, though not much except more curiosity was gained from this look. It was not until both voyager 1 and voyager 2 flew by and snapped pictures of Saturn’s moons in the 1980s that our curiosity was rekindled about the moons (and of course Saturn itself) and we began new missions to study them (NASA, 2004. "Voyager - Images - Saturn Images").
In the 1980s both the voyager 1 and voyager 2 space crafts where launched, and on their journey throughout our solar system they managed to capture a few photos of Enceladus (See figure 1).

Even with only a few photos, these managed showcased the various surface features, as well as the potential composition of the moon, which would later inspire further missions to study the moon more in depth.
In 2005 the Cassini space craft was the next to study the moon, now armed with more advanced technology and with a specific requirement to look at the moon. The Cassini craft was able to show us a closer and much clearer look at Enceladus allowing us to see its varied surface composition in picture and inferred imaging, as well as the features that make this moon stand out specifically (Weichman, "Discovering Enceladus").
From just these few missions alone we have gathered a great deal of information about Enceladus, including its surface composition, the conditions on and possibly below the surface, as well as the more interesting characteristics that the moon embodies. The surface of Enceladus is made completely of water ice, hence the reason why it reflects so much of the light that interacts with it; this makes it one of the brightest objects currently in our solar system. Its surface is also varied in multiple places with about 5 different types of terrain. In some areas of the moon we can see heavy cratered areas, more so in the eastern and northeastern areas. Other areas we can see that there are large valleys and ridges and large fissures that line some areas. In the western region of the moon we can see a much smoother region that looks nearly untouched, even by craters (See Figure 2) (Seasky.org, "Enceladus, moon of Saturn"). This varied landscape suggests that Enceladus is quite geologically active and shifts its surface quite frequently (thus ridding itself of any surface blemishes in some areas). This leads us to believe that there is a liquid interior to the moon, whether it is entire lakes or small pockets is currently unknown, but it is clear that they are large enough to cause crustal deformations as well as shift the surface.

The conditions on the moon itself are quite surprising as well as the temperature on the surface. According to the data collected by the Cassini spacecraft, Enceladus does have somewhat of an atmosphere and somewhat of an obscure magnetic field. While measuring the passing of a star behind Enceladus, the Cassini craft observed that the star was dimmed before going completely behind the moon, this suggested that there was some kind of atmosphere (made of mostly water vapor) around the moon (Hamilton, "Saturn's Moon Enceladus"). After further study it was found that the small atmosphere is not consistent throughout the entire moon, only the areas near the southern part of the moon are the most consistent as this is where the largest amount of heat and water vapor are located (more on that later). Cassini also measured the presence of an obscure magnetic field around Enceladus utilizing an instrument known as a magnetometer. The instrument detected a bending of the magnetic field around the moon, this was because of electrical currents that where generated by the interactions between the magnetosphere of Saturn and particles in the atmosphere of Enceladus (Hamilton, "Enceladus Atmosphere"). In Figure 3 we can see that the magnetic field bends more at the South Pole than at other areas around the moon, this is once again due to the larger increase in temperature and expelling of materials at that location.
Due to the large amount of light that is reflected from the moon the surface temperature of the moon is extremely cold, measuring at about -330 degrees Fahrenheit. There is however one other area of Enceladus where temperatures differ, this is at the south pole where there is a large increase in temperature ranging from -305 to -261 degrees Fahrenheit (see Figure 4 for temperature map) (Hamilton, "Enceladus Temperature Map"). This brings us to the area itself. The Cassini spacecraft found that at the southern pole is a “hotspot” of sorts; this area consists of four large fissures that have been dubbed the “Tiger Stripes”.
These stripes frequently vent materials out of the planet and up into the atmosphere. This is where the coincidences with the naming of the moon become even more apparent and quite funny when you consider that although those viewing Enceladus in the 1700s and 1800s where able to tell that the moon existed, they had barely any way of discerning detailed surface features let alone seismic and volcanic activities, such as the vents. These vents are known as ice volcanos, ice geysers, or cryovolcanos, which are capable of shooting material out at around 800 miles per hour (Davis , "Solar System Exploration"). This is fast enough for the material to break free of the moons pull and into the ring of Saturn that it is in, though some of the material does fall back onto the surface (Figure 5 and 6 for tiger stripes and ice volcano).
These two prominent features of Enceladus have lead scientists to draw several conclusions, first off that the planet does experience a great deal of tidal forces which cause it to heat up underneath (suggesting liquid water of some sort underneath). These gravitational forces cause the “Tiger Stripes to frequently open and close which then contributes to the pressure build up and the eventual release of water (which then freezes nearly the instant it gets to the surface). Enceladus is thought to be a large contributor to the icy material in Saturn’s E-ring as the materials in there are smaller particles and are mostly ice in composition. This also suggests that the material semi renews itself, with some of the material shot out from Enceladus coming back to the surface and with Enceladus traveling in the E-ring (causing some of the particles to then re-connect with the surface) (CAIN, 2009. "Saturn's Icy Moon of Enceladus").
But how can this liquid water exist underneath the surface of the moon, shouldn’t it still be too cold for liquid water to form even with the tidal forces contribution to heat? The Cassini craft also managed to detect various other chemicals present in the atmosphere and the areas with a high amount of vapor. One of these chemicals was ammonia which is thought to act as a type of antifreeze that is keeping the water from freezing under the surface (Redd, 2013. "Enceladus: Saturns Tiny, Shiny Moon "). It also detected several other complex chemicals which could suggest that it is suitable for hosting life of some sort under the surface.
Thanks to the voyager spacecrafts we know that Enceladus is only about 313 miles in diameter (1/25th earths size, earth being 7,917 miles in diameter), which can fit comfortably within the Gulf of Mexico (See Figure 7 for size comparison).

It was initially thought that Enceladus only had a density that was slightly greater than that of water, however a closer flyby by Cassini in 2012 indicated that the density was something closer to 30% that of earths. This suggests that it might have a considerably large and rocky core ("Enceladus", cseligman.com). With this new information it is thought that the core might also be a contributing factor to the heat produced in Enceladus, via radioactive decay of some heavy atoms.
Being such a small world it is no surprise that the gravity of Enceladus is only 1.1% that of earths and only 1/16th of our moons gravity. This being said the escape velocity required is also quite low, at about 353 miles per hour (earths is 25,000 miles per hour, and as we know it requires us to go to great lengths just to merely lift off, generally requiring multiple rockets in the process), which means that even something like an old WW2 plane could escape the gravitational pull of Enceladus (Redd, 2013. "Enceladus: Saturns Tiny, Shiny Moon "). This might be made even easier when Enceladus is being pulled on by Saturn and one of the other moons that are closer to Enceladus, as the alternate gravity pulling you away would possibly reduce the effort required to leave (even if just by a little bit).
As mentioned before, the moon Enceladus is located within Saturn’s E-ring at about 148 miles from Saturn itself (Figure 8). Enceladus’ orbits at a velocity of about 28,265 miles per hour, which means that it takes the moon around 33 hours to make a full orbit around the planet (our own moon orbits at 2,288 mph and takes around 27 days to orbit earth at a distance of about 238,900 miles) (Clarke, "Understanding Enceladus"). Since it is a moon of Saturn it is worth noting that it takes the same amount of time to orbit the sun as Saturn does which is about 29 years (this almost makes it a solar system within a solar system if you consider Saturn to be the sun in relation to its moons). Much like our own moon (and many others) Enceladus is tidally locked in its orbit, meaning that it takes Enceladus the same amount of time to rotate on its own axis as it does to orbit around Saturn (Russell, 2009. "Enceladus"). This means that one side is always facing Saturn while another is always facing away. Unlike our moon however, Enceladus does not have an elliptical orbit around Saturn and therefor would not appear to get any larger or smaller if viewed from a stable surface on Saturn.
With all the data we know thus far about Enceladus, with its potentially rocky core, its subsurface oceans, and its variety of heated areas, it is no surprise that more data is being gathered on this moon to show support for potential life. A recent article (published May 7th, 2015) by space.com states that scientists have uncovered more data about the oceans underneath the icy surface of Enceladus. In this study they found not only that the oceans underneath are salty (with a balance much like our own oceans), but also are host to a variety of other potential chemicals due to the rocky core under the ocean. By studying the ice and gasses that have been released from Enceladus they have been able to develop a model that estimates the saltiness and PH levels of the oceans. In their model they determined that the oceans where relatively basic, having a PH balance of about 11 to 12, (as stated before equivalent to ammonia) which is tolerable for some organisms that live on our own planet. In their study they also found that the oceans where full of a chemical known as Sodium Carbonate, which is also found on our planet in what are known as “Soda lakes” which are host to shrimp and other microbes (Wall, 2015 "Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life"). The interactions of the water and the rocky core are speculated to produce these high PH levels which also results in the production of molecular hydrogen. This hydrogen can then be used as a potential source of chemical energy for any developing life forms underneath, thus eliminating the need for sunlight (making the potential life forms gain energy from chemosynthesis rather than photosynthesis). As Christopher Glein states in the article “"Molecular hydrogen can both drive the formation of organic compounds like amino acids that may lead to the origin of life, and serve as food for microbial life such as methane-producing organisms” (Wall, 2015 "Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life").
With these new findings and what we already know, Enceladus is looking more and more promising for hosting life than ever before which is why there are a few projects in the works currently that are designed to explore and gather more data on Enceladus, in the hopes that we can find more definitive proof of life in our universe. As it is the Cassini space craft was originally going to be decommissioned in 2008, however it proved even more useful and is still going today. A project known as Enceladus Explored was launched in 2012 by the German Aerospace Center, this project will attempt to melt through the icy crust and dive into the oceans below to get better samples of the water when it is in its liquid state, thus providing us with a more accurate reading than we already have (2012, "Searching for life in the depths of Enceladus" DLR Portal). In addition to this there are other potential “Discovery” missions planned by NASA (one which is a sample and return mission and another which is titled JET: Journey to Enceladus and Titan) as well as a host of other ambitious upcoming projects to study the mysteries of the icy moon ( Kane, 2014. "Discovery Missions for an Icy Moon with Active Plumes").
Enceladus is like an ever varying story, going from myth to adventure to a now ongoing treasure hunt for our extraterrestrial brethren. From its ever varied surface to its explosive jets and to the mysteries that lie beneath it seems funny to think that this moon we are now so interested in and holds so much potential was once not even know about, and all that people knew of any Enceladus was from the Greek myths and legends. I will defiantly be interested to see what future missions and data holds for this shiny diamond in our solar system as it truly is one of those great treasures in our own backyard, and the best part is we’ve only just started digging around!

References

Redd, N. (2013, April 5). Enceladus: Saturns Tiny, Shiny Moon. Retrieved from http://www.space.com/20543-enceladus-saturn-s-tiny-shiny-moon.html

Blunck, J. (2010). Discovering and Naming the Satellites. In Solar system moons discovery and mythology (p. 56). Dordrecht: Springer.

Enceladus. (n.d.). Retrieved from http://www.greekmythology.com/Myths/Gigantes/Enceladus/enceladus.html

Voyager - Images - Saturn Images. (2004, December 6). Retrieved from http://voyager.jpl.nasa.gov/image/saturn.html

Weichman, J. (n.d.). Discovering Enceladus. Retrieved from http://discoveringenceladus.com/basics.html

Enceladus, moon of Saturn. (n.d.). Retrieved from http://www.seasky.org/solar-system/saturn-enceladus.html

Hamilton, C. (n.d.). Saturn's Moon Enceladus. Retrieved from http://solarviews.com/eng/enceladus.htm

Hamilton, C. (n.d.). Enceladus Atmosphere. Retrieved from http://solarviews.com/cap/pia/PIA06430.htm

Hamilton, C. (n.d.). Enceladus Temperature Map. Retrieved from http://solarviews.com/cap/pia/PIA06432.htm

Davis, P. (n.d.). Solar System Exploration. Retrieved from http://solarsystem.nasa.gov/planets/enceladus/indepth

CAIN, F. (2009, December 28). Saturn's Icy Moon of Enceladus. Retrieved from http://www.universetoday.com/48796/enceladus/

Enceladus. (n.d.). Retrieved from http://cseligman.com/text/moons/enceladus.htm

Clarke, A. (n.d.). Understanding Enceladus. Retrieved from http://hagablog.co.uk/demos/enceladus/enceladusthemoon/

Russell, R. (2009, January 22). Enceladus. Retrieved from http://www.windows2universe.org/saturn/moons/enceladus.html&edu=high

Wall, M. (2015, May 7). Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life. Retrieved from http://www.space.com/29334-enceladus-ocean-energy-source-life.html

(2012, February 22). Searching for life in the depths of Enceladus. Retrieved from http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-2751/#/gallery/4874

Kane, V. (2014, March 4). Discovery Missions for an Icy Moon with Active Plumes. Retrieved from http://www.planetary.org/blogs/guest-blogs/van-kane/20140402-discovery-missions-for-an-icy-moon-with-plumes.html?referrer=https://www.google.com/