Hi everyone. As you know, last time we took a look at 10 things you wanted to know about Uranus. This time, I thought it would be a great idea to consider some of the things you might find interesting about a tiny little place that’s been in the news recently. Enceladus.
Enceladus is the 6th largest satellite of Saturn. Despite the fact that she reflects almost all of the sunlight that strikes her, very little was known about this tiny moon until the early 1980’s when the Voyager probes passed close by.
2.How big is Enceladus?
With a diameter of only 500 km (210 miles) Enceladus is very small. (Only a tenth the size of Titan, Saturn’s largest moon).
3. So how was Enceladus discovered?
Enceladus was discovered in 1789 by Frederick William Herschell on August 28th 1789. He had spotted this moon a few years before with a smaller telescope, but, due to the fact that Saturn creates a very bright backdrop, failed to recognize she was there.
NOTE: Another factor that may have masked her discovery is the fact that Enceladus orbits within the densest part of the diffuse E band of Saturn’s ring system. (Interestingly, scientist think there may be an association between the two, and it is possible Enceladus is the source material for that ring)
4.What is Enceladus composed of?
This little moon has one or two surprises. Because of her tiny size, she was once thought to be comprised of ice. However, more recent findings show her to be denser and possessing a greater gravity than she should. We now understand Enceladus to have a silicate/nickel core surrounded by a much larger mantle of water ice. However, because of a mysterious internal heat source, she is also blessed with subsurface oceans (see point 5) AND – she has an atmosphere – comprised of 91% water vapor, 4% nitrogen, 3.2% carbon dioxide, and 1.7% methane.
5.Any other cool facts?
Oh yes! In 2005, NASA’s Cassini spacecraft espied geysers of ice and water vapour erupting from Enceladus’s South Pole. It has been suspected for some time that several of the bigger moons of the outer gas giants might harbour water – In frozen or liquid form. Europa, for example, an ice-sheathed moon of Jupiter is also known to possess a subterranean ocean. The detection on the geyser on Enceladus only aroused their suspicions further. Therefore, the Cassini project was tasked, amongst other things, to take a closer look.
Cassini arrived in orbit around Saturn in 2004. (It will stay there until September 2017, when it will be instructed to dive headlong into the giant planet’s thick atmosphere, and collect invaluable data as it dies.) In the meantime, Cassini has been busy. On April 3rd this year, researchers announced their discovery of a deep watery ocean on Enceladus, very similar to the one beneath Europa. Such a finding elevates Enceladus into the premier category of ‘must visit’ places for life-harboring locations in our solar system.
6.That must mean the surface is rather interesting?
Very true. Despite its small size, Enceladus has what is termed, a wide ranging surface, with evidence of old, heavily cratered regions and much younger, tectonically deformed terrain. (Smooth plains and harsh ridge-like formations). And of course, we see a lot of cryovolcanic venting due to internal heat.
7.So where does the heat come from?
Before the Cassini missions, very little was known about Enceladus’s internal structure. But, from what we can determine now, it looks as if this little moon is rich in radionuclides. (An atom with an unstable nucleus generated during the formation of Saturn) The action of radionuclides on her interior have melted part of her core, creating magma chambers that flex under the strain of Saturn’s gravitational tides.
BUT: That’s only part of the story. Flexing would only produce 1.1 gigawatts of energy. The southern polar terrain produces 4.7 gigawatts, suggesting thermal equilibrium. Scientists are unable to explain why such heat exists.
8.But what is cryovolcanism?
In a nutshell, we’re talking about volcanoes that erupt volatiles such as water, ammonia and methane instead of heated rock. (Collectively referred to as cryomagma). These substances are usually in the form of liquids, but can also occur in vapor form). In Enceladus’s case, her eruptions create winter wonderlands of falling snow. (But – sadly – even Santa would find this place too cold to live).
9.The South Polar Region is thought to be particularly distinctive. Why?
Images taken by Cassini revealed a distinctive, tectonically deformed region surrounding the South Pole area, reaching as far north as 60⁰ in the southern latitude. The area has few sizeable impact craters, suggesting that it is the youngest surface on the moon. Near the center of this region are four fractures bounded on either side by ridges called the ‘tiger stripes’.
These fractures appear to be the youngest features in this region and are surrounded by course-grained mint green water ice. Results from the visual and infrared spectrometer (VIMS) instrument suggest this green colored material is chemically distinct from the rest of the surface of Enceladus. Interestingly, VIMS also detected simple carbon-containing organic compounds in the tiger stripes, chemistry not found anywhere else on this tiny moon.
10.Does the discovery of water mean Enceladus will play a part in future projects?
It certainly looks that way. Scientists are in agreement that we desperately need to take a closer look at both Enceladus and Europa.
For example, Jonathan Lunine of Cornell University has stated, “I don’t know which of the two is going to be more likely to have life. It might be both; it could be neither. I think what this discovery tells us is that we just need to be more aggressive in getting the next generation of spacecraft both to Europa and to the Saturn system once the Cassini mission is over.”
Ah, but wouldn’t Enceladus be difficult to get to and even more difficult to salvage specimens from? Well, yes and no. Yes – it’s a long-long way away. However, once there, obtaining samples would be much simpler than trying to obtain the same materials from Europa. Why? Because Enceladus’ geysers actually blast their reactive materials hundreds of miles out into space. So, if it can be proved those ejectiles actually originate in the subsurface oceans, then in effect, we can collect samples from orbit! Ta-dah!
(Obviously, scientists can’t be sure of the source of the material in the plumes at the moment, but, by the time a craft is dispatched, we’re sure they will.) In fact, Cassini has already completed some homework on this subject, by using its mass spectrometer. So far, the results are encouraging, as it has detected a range of salts and other organic compounds that represent the carbon-based building blocks of life.
However, we have to remember that Cassini’s mass spectrometer can only detect relatively light organic compounds. Therefore, follow-up missions will have to employ more advanced and much more sensitive detectors.
Whatever the outcome, it looks like our very own solar system will continue to be a place of wonder and mystery for some time to come.
Next time, we’ll take a closer look at the other Moon mentioned in this report, Europa, and see what’s new there.
Until then – have a great day