The most interesting things in the Solar System don't have to be planets. Some of the greatest prospects for harboring life are in fact moons.
Moons are also very geologically diverse in ways that are truly unimaginable. If you only count the moons of the planets, there are 166 known moons in the Solar System. Here is the breakdown:
Mercury and Venus-0.
Some of these moons are only 8-10 miles across, and in some instances, 3 billion miles away from us orbiting Neptune. I must admit, while it's impressive we know about them, a cold lump of rock 3 billion miles away isn't that interesting.
That's why this is only a top 10 list and not a top 166 or top 100 list. There are a handful of moons that harbor secrets that are fascinating. Here are the ones that make the cut.
If the Batman character Two-Face had a favorite moon, it would definitely be Iapetus. This moon orbits Saturn and has a few very peculiar features about it.
Firstly, one half of the entire moon is black as coal, and the other half is as white as Arctic snow:
And no, I'm not just misunderstanding shadows. Apparently during the typical orbit of Iapetus, because it is "tidally locked" to Saturn, one hemisphere is exposed to ring debris and the other is not. The color difference also creates a temperature difference across the two faces, and so the surface material (primarily water-ice) migrates from one side to the other via sublimation.
Despite my poor attempt at an explanation, there is one other surface feature that no one can explain:
In the middle of moon there is a ridge that goes more than halfway around the moon and is a few times taller than Mt. Everest! See for yourself:
That ridge makes Iapetus totally look like a walnut or something. The feature is unique to Iapetus, and we honestly don't have a good clue why it's there.
According to Wired science, scientists recently discovered giant ice avalanches on Iapetus. If that wasn't cool enough, they apparently travel a lot farther than they should. This created speculation that the ice sheets ride on cushions of trapped air.
Is that Iapetus bidding for a higher spot on the countdown? Probably. Unfortunately for Iapetus though this list is final.
For a moon to be named Titan it has to be big. Titan is Saturn's second contribution to the countdown, and it boasts so impressive facts:
- If viewed side by side to Mercury, it would be larger
- Despite being larger, it is only 50% as massive
- Despite being less massive than Mercury, it's 80% more massive than our Moon
- It is so large that it noticeably affects the orbit of nearby moons
Size alone however does not make this countdown. Titan is really cool because it is like the baby version of Earth. If the Earth had baby pictures, they would look much like Titan. This is because its atmosphere is composed primarily of nitrogen and it has traces of methane (like us before the whole organic life thing came along).
Titan is the only other confirmed Solar System body to have lakes, rivers, deltas, and seas:
Before you get too excited, you have to realize that these lakes are probably mostly liquid methane. Still, most of the building blocks for life exist on Titan. Scientists can in no way rule out that there is something living there.
Oh and instead of a water cycle, Titan has a liquid methane cycle. I feel like that would be a photographer's dream to spend a day on Titan and photograph these events take place (and hopefully survive too).
I was recently reading how they found a river on Titan that was eerily similar to the Nile river here on Earth.
Uranus makes the countdown with its beloved moon Miranda. Miranda is definitely an oddball, and at one point in its history was probably the most geologically active moon in the Solar System. So now it looks like this:
Once again, scientists are puzzled about how this came to be. After all, the canyons on Miranda are often 12 times deeper than the Grand Canyon. Refresher:
12 times deeper than that. What's at the bottom of the Grand Canyon? Oh yeah, a river.
Scientists are fascinated yet troubled by the intense ridges. The most common theory involves cryovolcanoes. Not only does that sound cool, that's scientist slang for ice volcanoes. I would pay to see that eruption for sure.
Lastly, I couldn't resist. If you go mooning on Miranda, Ur-anus will take up most of the sky (It's the closest moon to the 7th planet)...
This is already Saturn's third contribution to this Top 10 list. The other planets need to step up their collective game, pronto.
Enceladus might not be a looker. He/She (name means children of a Titan) makes up for it in other areas though. Remember the cryovolcanoes I mentioned when I talked about Miranda? They've actually been observed on the poles of Enceladus in the act of erupting. The water that doesn't make it to space falls back to the ground as snow. Yes, a moon that resides in the same Solar System that you do has a weather pattern where it snows.
If that doesn't do it for you, it also has extensive water supply at or near the surface. This water is salty, a.k.a. the same composition of 70% of the surface of your planet. Whatever the water's activity is, it has also some mechanism to erase evidence of craters at the poles. In short, Enceladus might be one of the first places we look for alien life.
Also, Enceladus is a ring manufacturer. The debris and chemicals that it spouts off on a regular basis often find themselves contributing to the construction of the rings of Saturn.
#6 Umbriel and Oberon
Okay, I cheated. Shoot me. I chose to do two moons instead of one because Umbriel and Oberon would not have made the countdown by themselves. But together, they're quite interesting.
They also both orbit Uranus, and both have unique geological features.
Umbriel is the darkest of all Uranus's moons. What makes it famous though is the Wunda crater. This specific crater is located on the north pole of Umbriel, and it has a very bright ring-shaped floor that is about 20 km across.
We have literally no idea what this could be.
Your guess is as good as anybody's. With that in mind, my guess is that the Soviet Union tested a radioactive chicken ring WMD during the Cold War. When preliminary tests showed it was too powerful of a weapon, they shot it at Uranus.
Oberon is the most heavily cratered moon that orbits Uranus. It has peculiar craters as well: many of them in the leading hemisphere have an eerie dark substance at the bottom of them. Also, the trailing hemisphere is much less red than the leading hemisphere which makes Oberon have the two tone look that Iapetus (#10) does.
Io, Io, it's off to the most volcanically active solar system body we go.
Despite my poor attempt at song writing, I will have no trouble describing to you one of the craziest moons in our neighborhood.
- Mountains taller than Mt. Everest- Check
- Historical significance- Check
- 100% unique surface features- Check
So where do I start?
Well, the eruptions on Io are pretty intense. They can shoot out sulfur gas at a speed of 1,000 m/s, or about the speed of an M16 round. The gases have been observed to travel 300 miles high, which is about 1500 Eiffel towers stacked on top of each other.
Oh, and there are 330 ft. high waves on Io. But wait, you say, Io doesn't have water.
The waves are waves within the crust of the planet. Where our moon creates waves in our oceans, Jupiter creates waves in the crust of Io.
I'm going to try to put this in perspective. Have you heard of Krakatoa? It was a volcanic island that basically spontaneously combusted and killed 36,000 people in 1880. The tsunami waves caused by this explosion were slightly smaller than a large daily wave in the crust of Io. Imagine a tall wave of solid ground coming at you.
My conclusion is that Io is one moon that I will leave off the list of moons I want to visit (which is actually a pretty short list).
The historical significance? It was used in the first accurate measurement of the speed of light. Pretty cool.
In Greek mythology, Triton was a God of the Sea. He had a long eel-like appendage coming out of his torso instead of legs, and I've heard he was good with the ladies.
Anywho, if Triton were to visit the moon that bears his name, he would freeze. Immediately. Triton is a large moon of Neptune that is vastly larger than anything else that orbits Neptune. You can see this by this graph:
It is also the only "large moon" in the Solar System to rotate the wrong direction around its planet. Scientist think that since Triton doesn't walk like a Neptune moon, and it doesn't talk like a Neptune moon, it probably wasn't originally a moon of Neptune.
It is also colder than probably anything you've ever witnessed. A good standard for cryogenic cold on Earth is liquid nitrogen. The surface of Triton is solid nitrogen (a.k.a. frozen liquid nitrogen).
The volcanic activity on Triton involves molten lava spewing out at thousands of degrees. Just kidding, it's basically nitrogen (Earth's air) shooting out at freezing temperatures. The "lava" flows are water and ammonia. But for anything on Triton, that's really warm. Also, it's probably really beautiful.
Lastly, your ears might pop if you set foot on Triton (among other things). The atmosphere is 1/70,000th the pressure of Earth's atmosphere. That's thin.
#3 THE Moon
"Oh, baloney!" you might say. I look up into the sky and see this thing every night! It can't be that interesting!
Sure, I'm not going to give you a recap of the Apollo missions. However, there are some recent developments that might peak your interest.
The Moon has water
Bucketloads too. At least 158 billion gallons according to the NASA. That's about 15% of Lake Erie. That doesn't sound like much, but it could supply a moon base for hundreds of years. Also, it's near the surface. However, it seems almost impossible to harvest. A recent study showed the water probably originated on Earth.
The Moon had volcanoes at one point in its history
The Moon, like the Earth, is composed of different layers. The Moon's mantle was at one point very active. That means at one point during the Earth's history, an observer could have looked in the sky and seen a volcano erupting on the Moon. Yes, that was billions of years ago. Specifically, it is now believed eruptions occurred from 4.2 billion years ago to 1.2 billion years ago.
The Moon is composed of the same materials as Earth
Not just partially, either. Even the same titanium isotopes are found on both the Earth and the Moon, and that's significant. That's kind of like the same signature being on two different pieces of artwork. The Earth and the Moon probably came from the same place. The Moon has different concentrations (not isotopes) of Iron, but it is thought that these concentrations resemble the outer layers of the Earth.
Despite what you might hear, we aren't 100% sure how it formed
The prevailing theory was that a Mars sized body collided with Earth 4.5 billion years ago. The subsequent collision involved the incoming planet blowing incredible amounts of material into space, and most of this material stuck around because of the gravitational pull of Earth, and it eventually coalesced into the Moon. While we are pretty sure of the Moon's age, that prevailing theory still has some significant gaps in it (which mostly has come to light as of 2012).
What would the Earth be like without the moon?
Here is an article on that subject.
Is the moon landing a hoax?
12 people have stepped on the moon. If you need proof, there is an entire MythBusters episode devoted to testing to see if the landing was a hoax. That might not be enough for you, but it's definitely worth checking out. The biggest proof that I remember is that when one shines a powerful laser at the Apollo 15 landing site, and nowhere else on the moon, laser light bounces back and we can detect it. That's because NASA left a special kind of reflective mirror at that site.
We are nearing the end of the countdown as only two moons remain. They also happen to be two of my favorite looking moons. Ganymede, #2, is THE largest moon in the Solar System. So large, in fact, that it is larger than Mercury and Pluto. Also, it's 3/4 the size of Mars.
According to ancient Chinese astronomical records, Ganymede was discovered with the naked eye of a Chinese astronomer in 365 B.C. If so, he was the most astute person in history. Although this sounds like a tall tale, it would be possible to see Ganymede with the naked eye if the stars aligned (I just said that for pun).
It was re-discovered in 1610 by Galileo. This was a significant moment. At one point Galileo realized, holy stars Batman, not everything revolves around Earth. The Catholic Church has been on the defensive ever since.
Galileo was tortured and then put on house arrest for his discovery and defense of four Jupiter moons and the consequences of their orbits.
Luckily, today, we know even more about these moons and we don't have to worry as much about the pesky Inquisition.
Anyway, besides being pretty, Ganymede has some interesting features. It is the only moon in the Solar System to have a magnetosphere which makes it more like a planet and and also makes it sound more like it came out of X-men.
It also probably has a saltwater ocean under the surface, and it is one of the few places in the Solar System where you will find large concentrations of Oxygen. Not the Oxygen levels like you and I would prefer, but still, a decent amount.
Ganymede also, like the Earth, has tectonic activity and young surface features. It isn't obvious to scientists why some of the surface appears very young and some of it appears very old, but hey, at least we are sending more spacecraft its way in the next couple of decades.
Oceans, Oxygen, and plate tectonics. Let's go ahead and book a space trip. Probably our primary challenge, besides cosmic radiation, would be freezing temperatures. Somewhere on the order of -260 degrees Fahrenheit cold. On the other hand, microbial life might find it suiting...
Okay, numero uno. Europa fought valiantly for this spot, disgracing the other moons through competition and mockery.
Why number one? Probably because it is by far the best candidate to find life.
Okay, where do I start. It helps that it has a rocky core and metallic mantle similar to Earth. It helps that the atmosphere is mostly molecular Oxygen. The largest factor though is that it has a saltwater ocean deep enough to cover the entire surface of the moon. Unlike other planets, this ocean is not buried deep within the surface, and it doesn't have much else besides water. The ocean does have an ice layer on top, similar to the Arctic on Earth, but this ice has cracks that stretch for thousands of miles. Considering there is life below the ice in the Arctic and Antarctica, it wouldn't be much of a stretch to say that life could exist on Europa.
Here are some other polar sea creatures.
Since the Europa ocean is believed to be in constant motion, it is believed to be relatively warm (it has to be if it's liquid water). Also, the surface ice moves relative to the rocky surface underneath due to the water movement. That's like an eggshell rotating around the yolk. Every 12,000 years it is believed to complete one rotation.
So, I have to admit, we aren't sure that all this is the case. We do have evidence of icebergs and lakes, but right now we simply can't draw scientific conclusions. We're pretty sure there is about twice as much saltwater on Europa as there is on Earth.
You can help find out though by lobbying for space exploration. If you've made it this far in the article, you're probably fairly interested in the possibilities. I, for one, would love to send a cryobot like this one to explore the waters of Europa during my lifetime:
me on April 29, 2019:
Luke on April 29, 2019:
Thanos is my dad ;)
Robert Sacchi on July 05, 2015:
Thank you. You make a great case for all of the moons on your list. Did you consider making a top 10 list of heavenly bodies in our solar system?
Arun Dev from United Countries of the World on June 29, 2015:
This hub was nice to read.
Greensleeves Hubs from Essex, UK on June 10, 2013:
cydro; when I was a kid all sensible scientists seemed to know that moons were barren lumps of rock which all looked pretty much like our Moon. Now we know we don't have to be sensible because the moons aren't - many of them are freaky, weird and bizarre.
I like your humorous style of presentation and I like your selections, all of which I can pretty much agree with. I'm not necessarily 100% with you on the order though - I think I might have put Titan and Io at No1 and No2. What else do you want from Titan? Palm trees around the poisonous lakes? Water voles nesting in the methane riverbanks?? I guess though, the moment life is discovered in the oceans of Europa or Enceladus, then all else will pale into insignificance. I agree - probes should be dispatched to Europa as soon as it is practical to do so. One last point - Like it or not you may have to revise your list eventually - in several tens of millions of years time, Triton is expected to crash into the surface of Neptune.
Excellent lighthearted page to encourage interest in the moons of the Solar System which will hopefully attract some younger enthusiasts to the subject. Voted up.
Blake Atkinson (author) from Kentucky on April 10, 2013:
Thank you Mr. Swan! This is probably my favorite hub I've ever done. I really hope we send probes to these places soon.
Thomas Swan from New Zealand on April 06, 2013:
I must say, I like your concise and humorous writing style. This is a great hub, full of fascinating facts. Standing on Miranda and seeing Uranus reflected in the Sun would be a sight to behold! Saturn certainly seems like a fertile region of the solar system too... plenty of water, shame it's all so cold! I suppose we'll be using that water one day when we colonize those moons. My pick would be Miranda, though Europa would be pretty close!
Erika on March 01, 2013:
What an awesome article! I love researching space and this is one thing that would come in handy. I have always been most interested in Titan.
Blake Atkinson (author) from Kentucky on July 28, 2012:
Thanks cryptid and Reynold. That novel sounds interesting I'll have to check it out!
Reynold Jay from Saginaw, Michigan on July 26, 2012:
You have the makings of a book for children here too. I was a science teacher for Special ed kids and we never got to the moons and all this was new to me. I wonder if a science movie along this line has been done too. This had to be a lot of work to put this together and arrive at the moons in the order you selected. From your article,here and there , it is apparent you are more than a casual observer, as I often contemplate things we discover in space and try to make some sense of it. The Galileo story is imortant for everyone to know and it is good you told it so succinctly. Well done as always and little wonder I am probably your biggest fan. IF you ever get around to reding fiction, I would bet you would love my novel "Seeds from Heaven" Which deals with science and religion. RJ
Luther Urswick from USA on July 26, 2012:
What an amazing, well-written Hub. I immediately thought of Europa when I saw the title, but I learned a lot here, especially about our own moon. Great job!
Blake Atkinson (author) from Kentucky on July 25, 2012:
Thanks guys for the encouragement. I really appreciate it.
gingerka from Colorado on July 25, 2012:
Your article has interesting information and GREAT pictures. Thanks
Rui Carreira from Torres Novas on July 25, 2012:
This is an outstanding article... Great nugget and I sincerely congratulate you on this!
I voted it up and interesting! Keep producing content like this and you will get far!
point2make on July 25, 2012:
I liked your choices. The moons of our Solar System are varied and a most interesting lot. Your hub was informative, enjoyable and well done. Thanks for the lesson......I enjoyed it. Voted up.