The Moons of Saturn:
Much like the Jovian system, the Saturnian system is riddled with moons of all shapes and sizes. There are currently 62 recognized moons of Saturn, meaning that although there are technically billions of objects orbiting Saturn (the rings), only a few of them are large enough to be considered moons. Of these 62, only 53 have been named and only 13 of them have a diameter of larger than 50 (just over 31 miles) kilometers, so most of the objects orbiting Saturn are pretty puny and uninteresting. For the purposes of this blog, I am going to focus on 7 of those moons that are larger than 50 km, as they are by far the most interesting and the most explored. For your reading pleasure, here are bios of those 7 moons:
Titan - With a diameter of 3,200 miles, Titan is 200 miles wider than the planet Mercury, making it the second largest moon in the solar system.
The two largest moons in our Solar System pictured above next to Mercury.
Titan, apart from its size, is best known for being the only moon in our solar system with a thick, planet-like atmosphere. Before the Voyager missions, very little was known about the solar system, let alone Titan. However when Voyager first flew by, it captured this image below.
Titan!
This image was the first ever image of Titan taken by Voyager and for that matter was the first ever close up image of Titan ever taken. It was also the photograph to prove that the yellowish color of Titan was in fact, an atmosphere. This atmosphere is what makes Titan so interesting and is the reason why Titan is so far the most explored Moon in our Solar system besides our own.
First image of Titan taken by the Hubble Space Telescope (notice the thick atmosphere).
It wasn't until the Hubble Space telescope came around in 1990 that we finally got clear images of Titan and even then (as you can see) we were still unable to penetrate below Titan's thick atmosphere. Because of this lack of serious data, NASA and other space agencies collaborated to create what would be known as the Cassini-Huygens probe. This mission departed from Earth in 1997 and didn't arrive in the Saturnian system until 2005. However, when it did finally arrive, it gave us everything we asked for and more. The mission itself had two parts: The Cassini portion of the mission (which to this day is ongoing) was designed to get in orbit around Saturn and gather data from orbit. The Huygens portion of the mission was a probe that, upon arrival in the Saturnian system, would detach and descend into the atmosphere of Titan and land on the surface. While this mission was not designed to be a lengthy one like the Curiosity Rover on Mars, it was designed to send data and hopefully some images back to Earth.
The first image of a body in the outer Solar System taken from the surface. A serious scientific milestone.
Sure enough, after touching down successfully on Titan, the Huygens probe, during its 90 minutes of functionality, sent back the above image. While this is not the exact color of Titan's surface, it's about as close as we can get without actually being there ourselves. This was an amazing moment for NASA and honestly for the entire world; the first image taken from the surface of a body in the outer solar system, truly incredible. Cassini however, would be the main focus of the mission and to date has provided us with amazing images and data about Titan.
One of the first images of Titan's surface taken by Cassini. Cassini was the first time we had the opportunity to image the actual surface of Titan from orbit.
We now know intimate details about Titan, especially the surface. Titan's surface has an average temperature of about -290 degrees F, so cold in fact, that methane is a liquid. As a matter of fact, liquid methane shapes Titan's surface in amazing ways. Not only are there clouds of methane and methane rain, there are also entire lakes of liquid methane dotting the surface of Titan (in case you were wondering the black splotch on the image above is not a giant methane lake but more likely a desert like region).
The blue regions (not true color) have been darkened for emphasis. Anything blue is a concentration of liquid methane.
Here however, are images taken by Cassini of the liquid methane lakes on Titan. These lakes tend to be concentrated near the poles of Titan, however there are deposits of methane on the entire surface. There are numerous geologic features that on Earth would be shaped by water but on Titan are shaped by methane. These lakes are being closely studied by NASA and the Cassini team because they all believe that Titan is an excellent example of what planet Earth looked like about 4 billion years ago. Titan and Earth has similar chemical and physical make-ups and both have a thick atmosphere (Titan's is twice as thick as Earth's). Scientists believe that if we can understand what it is that makes Titan tick, we might be able to understand how our Earth transformed into the life-rich planet it has become today.
Obviously, Titan still has a wealth of information that it has yet to reveal to us, but NASA's Cassini mission (which orbits the Saturnian system) has been extended until 2017, at which time it will fall into Saturn and eventually be crushed by the massive pressure. Until that time though, let us hope that we continue to get amazing images of the Saturnian system just like the one below.
Titan imaged in three wavelengths by Cassini (natural color, near infrared, and true infrared)
Despite the fact that we know more about Titan than just about any other Moon in the Solar System, there are still 6 more moons I want to discuss.
Rhea -
Rhea taken by Cassini
Rhea is the second largest moon of Saturn and the ninth largest moon in the solar system, however with a diameter of only 949 miles, it is just over 1/3 the size of Titan. Rhea is just about the most boring moon/body in the Solar System. With no geologic activity, no atmosphere, no water of any kind, and no truly unique geologic features, Rhea is just another giant rock floating in space. NASA has no plans to visit it and it one of the least imaged moons of the Cassini mission. The only thing to look forward to on Rhea would be the sensation of being on a body that doesn't rotate. Rhea is tidally locked to Saturn and thus always has the same side facing Saturn and the same side facing away. How awesome it would be to freeze to death on the dark side before coming over to the light side and...freezing to death.
In case you were wondering, here is the size comparison for Earth, our Moon, and Rhea.
On to the next moon!
Iapetus -
Iapetus as imaged by Cassini
Iapetus is the third largest moon of Saturn. With a diameter of 912 miles, it is only slightly smaller than Rhea. Iapetus, unlike Rhea, actually has some very interesting features that make it far superior to Rhea; kind of like a twin that got more nutrients in the womb.
To start, Iapetus is composed of nearly 3/4 water ice, giving it a density barely thicker than liquid water. Despite being nearly the same size as Rhea, it is only about half as massive. Because of Iapetus' composition, its surface is quite dynamic and has one of the most unique features in the solar system. One glance at the photo above, shows that some parts of the surface are black, reflecting almost 0 light. While other parts, because they are water ice, reflect an enormous amount of light out into space. In the image above, you can also see the largest crater on Iapetus, which is just under 400 miles across. However, the most insane feature of Iapetus, one that completely blows my mind, is shown on the image below.
Notice the ridge that runs along the equator and how some parts of the surface are much brighter than others.
Dione (pronounced die-oh-nee) -
Dione as imaged by Cassini
Dione is Saturn's fourth largest Moon and has a diameter of 698 miles. This moon marks the beginning of the extreme drop off in size for Saturn's moons as Dione is a full 250 miles narrower than Rhea. Dione, much like Iapetus, is majorly composed of water ice, which provides us with some very interesting geologic features. Notice in the image above, the white wispy formations that seem to streak across Dione's surface. These white streaks are collapsing ice and rock as Saturn exudes its enormous gravitational forces onto Dione. Besides these streaks on the surface, Dione is pretty dull and doesn't have all that much going on personally. However because Dione is close to Enceladus and Saturn's rings, it is pretty much constantly bombarded by ice particles which, due to the extreme cold of the Saturnian system (-290 degree F), are harder than rock. So, next time you travel to Dione, be sure to bring some form of protection from the hail storms of death.
Dione orbiting close to the rings of Saturn
Tethys -
Tethys as imaged by Cassini
Tethys has a diameter of 660 miles, making it Saturn's fifth largest moon. Tethys is one of the most interesting moons in the Saturnian system because of its incredible geologic features. To start, Tethys is less dense than water, therefore scientists believe Tethys to be composed almost entirely of water ice with trace amounts of silicate rock. Tethys' composition has helped to create two of the largest geologic features in the solar system. The first of these features is known as the Odysseus Crater and can be seen in the image above. The Odysseus Crater is over 250 miles across, making it one of the largest in the solar system. The asteroid that made this crater, under normal circumstances, would have destroyed Tethys.
Here is an image of Tethys. On the left is the true color and on the right is an infrared image. Notice just how large the Odysseus Crater is (it is nearly 2/5 the diameter of Tethys).
However, scientists believe that early on in its life, Tethys was a bit warmer and thus squishier (due to all of the liquid water) and was able to absorb the bulk of the impact. This lucky break may have also contributed to the second geologic feature of note on Tethys, the Ithaca Chasma.
The lines you see are just part of the Chasma.
The Ithaca Chasma extends for 1200 miles across the surface of Tethys, nearly 3/4 of the circumference of Tethys, and is about 60 miles wide and 3 miles deep. Scientists have two possible theories as to the origins of this chasma. They believe that, as it is mostly on the opposite side of the Odysseus Crater, the impact formed from said asteroid might have formed the chasma. The other theory is that, as Tethys was much softer and had a lot more fluid in its early life, that as it froze and expanded, it literally tore itself apart. Both of these theories are valid explanation and we may in fact never know exactly what caused the Ithaca Chasma to form. Tethys, a tiny moon around Saturn, has some of the largest geolgic features in the solar system, very cool.Enceladus -
Enceladus as imaged by Cassini (blue color is only to show certain geologic features. not true color)
Enceladus is one of the most exciting moons in the solar system. With a diameter of about 310 miles it isn't even a tenth the diameter of Titan. However, scientists believe that underneath the surface of Enceladus lies an ocean of liquid water. Several questions come up when presented with this fact, such as, how can there be water when its' so cold? Or, how can we look below the surface and tell that there is water? All of these questions, while difficult, have relatively simple answers.
Jets of water shooting out of Enceladus.
As you can see from the above image, water has been imaged shooting out of Enceladus into space. Enceladus is one of only three bodies in the solar system where any kind of volcano or geyser has been witnessed erupting. Water is able to remain a liquid below the surface because Enceladus is very close to Saturn, about 110,000 miles away. While this might seem very far away, dont forget that our moon is 236,000 miles from Earth, so in fact, Enceladus is twice a close to its host planet as our moon is to us. This proximity to Saturn not only heats up Enceladus but it also squishes it and squeezes it as it orbits, breaking up much of the sub-surface ice. We can actually see this process going on beneath the surface because of the way the surface is cracked and jagged in parts.
Note the many cracks on the surface. The colored portion is an infrared image taken by Cassini. This proves that not far below the surface, there are warm spots where liquid water almost certainly exists.
The surface of Enceladus is one of the most reflective natural sources ever observed in the universe. It reflects nearly 100% of the light that it absorbs from the Sun and other sources, pointing again to its water ice and liquid water composition. This liquid water has NASA very interested in the possibility that life could exist below the surface of Enceladus. In 2011, scientists from NASA said that besides the Earth, Enceladus is becoming the greatest candidate for extraterrestrial life in the Solar System. As of right now, there are plans for a 2020 mission to Enceladus to see whether or not the Moon does in fact support life. I am seriously giddy with excitement.
Mimas -
Mimas with Herschel crater visible.
Finally we come to the last moon in this blog, Saturn's moon Mimas. Mimas has a diameter of 246 miles, making it quite a puny moon. However, Mimas has two things about it that are absolutely awesome. The first is that Mimas is the smallest body ever observed to have self-gravitationally become a sphere. When bodies become massive enough, they gravitationally collapse on themselves, turning into sphere like shapes. Mimas appears to be about as small as a body can get while still being able to collapse into a sphere. This fact however doesn't even come close to being the best thing about Mimas.
Mimas and The Death Star
This, is the best thing about Mimas. It looks uncannily like the Death Star from Star Wars. The really cool thing is that when Star Wars first came out, we didn't have this detailed of an image of Mimas so there is no way this similarity is intentional. Something about that makes me really happy, unless of course Mimas is in fact the death star. In which case we should probably find a way to take down its shields and blow it up.
Thanks so much for reading this blog on the Moons of Saturn! This is why I love space.
