Our solar system is made up of the Sun and its nine planets (eight really, since Pluto got the boot). The planets get so much attention that it’s easy to overlook the fact that there are a lot of other interesting things in our solar system - like moons. And a lot of them are just as interesting as the planets they orbit.
10. Ganymede - The Big One
At first glance, Ganymede looks a lot like Earth’s moon, but there is one huge difference: the size. Ganymede is the largest moon of Jupiter and, indeed, the entire solar system. It’s so big that it has its own magnetic field, something that no other moon does.
In fact, its size falls between the planets Mercury and Mars (8% larger than Mercury and 3/4 the size of Mars). If Ganymede were orbiting the Sun rather than Jupiter, it would be considered a planet, so it’s essentially a planet orbiting another planet. Or as Leonardo DiCaprio would call it, planet-ception.
9. Miranda - The Ugly One
We could make an inappropriate joke about how all the ugly moons orbit Uranus, but Miranda really is the ugly duckling of the solar system. At first glance, it looks like whoever was in charge of making the moons just threw together some leftover parts and sent them sailing around Uranus.
Miranda has some of the most varied landscapes in the solar system. Its sweeping patches of ridges and valleys, called coronae, can’t be found anywhere else in ours, and it has enormous canyons, some 12 times deeper than the Grand Canyon. If you dropped a rock off of the highest cliff on Miranda, it would take ten minutes to reach the ground below.
Scientists, as scientists are wont to do, love arguing about the reason for Miranda’s strange features. Some think that there was a large collision in the moon’s past that smashed it apart. Others think that meteorite strikes could have partially melted the surface and it hardened that way. Still others theorize that intergalactic space wombats strip-mined Miranda in their ever desperate search for space gold (citation needed). We may never really know.
What we do know is that Miranda is named after a Shakespearean character who never married, and no wonder. We seriously doubt this Miranda had a date for her senior prom either.
8. Callisto - The Most Cratered Object In The Solar System
Callisto, a moon of Jupiter, is the acne-plagued teenager of the solar system. Unlike most bodies of its size, Callisto has no geological activity to weather its surface (it’s the largest body in the solar system without any), so the craters pile up over the eons. The surface of Callisto is 4 billion years old, making it the oldest unchanged surface, and the most heavily cratered object in the solar system. The areas that are craters greatly outnumber the areas that are not.
There are so many craters on Callisto, that they’ve started to pile up on top of one another. There are even some places where there are concentric rings of craters within craters.
First planet-ception, now crater-ception. Jupiter must love its Leo DiCaprio movies.
[More information: 1. Callisto: Overview, 2. Callisto (moon).]
7. Dactyl - The Asteroid Moon
At only a mile wide, Dactyl is the smallest moon in the solar system. See the picture above? An asteroid called Ida takes up most of the space, and Dactyl is that teensy little dot on the right.
Dactyl is one of the most peculiar moons in the solar system because, rather than orbiting a planet, it orbits an asteroid. In Greek mythology, Ida was a mountain that was inhabited by creatures called Dactyls, so it makes sense that the asteroid’s sole “inhabitant” should bear that name.
Dactyl has answered a lot of questions about asteroids that were previously unknown. For example, it was possible to determine the mass and composition of Ida by studying Dactyl’s orbit. Also, before Dactyl’s discovery, astronomers thought that asteroids were just too small to have moons. Nope.
6. Epimetheus and Janus - The Moons That Narrowly Avoid Collision
Epimetheus and Janus are two moons of Saturn that share almost the same orbit, which is probably the result of them being the same moon a long time ago. But here’s the thing: every four years, they switch places in a near-collision.
The closest the moons come to one another is 6,200 miles, which may seem like a lot, but space is really, really big.
[More information: 1. Epimetheus: Overview, 2. Janus: Overview.]
5. Enceladus - The Ring-Bearer
Enceladus is one of the inner-most moons of Saturn. It is one of the most reflective bodies in the solar system, reflecting almost 100% of the light that hits it. It also has geyser plumes that spew ice and dust particles into space.
While the NASA probe Cassini was orbiting Saturn, it took this photo of those geysers:
And what’s even more astonishing: those geysers are the source of Saturn’s E-ring. The particles they spew out get caught in Saturn’s gravity and eventually constructed one of the rings over time. And it makes sense, since Enceladus is orbiting directly in the E-ring. In the below pic, Enceladus is the tiny, tiny black dot in the middle of the ring.
4. Triton - The One With Ice Volcanoes
Triton is the largest moon of Neptune. It’s also the only moon in the solar system that orbits its planet in the opposite direction of the planet’s rotation.
Triton is one of the only moons in our solar system that is volcanically active, but whereas volcanoes elsewhere spew out lava, Triton’s erupt liquid water and ammonia that freeze on contact with the frigid outer temperatures. To put that in layman’s terms: freaking ice volcanoes, OH MY GOD.
It is also very bright and reflects a lot of light because the surface is covered in ice – but not water ice. Triton is one of the coldest bodies in our solar system. You’ve heard of liquid nitrogen, right? That stuff that is incredibly cold? Triton is so cold that nitrogen freezes and creates that reflective layer of ice.
3. Europa - The One With Vast Oceans
Europa, another moon of Jupiter, has one of the smoothest surfaces in the solar system. That’s because the entire moon is a single ocean of water with an ice crust on the surface.
But just like the soft, gooey cheese hidden inside pizza crust, a liquid ocean of water exists beneath this icy shell due to tidal heating from Jupiter. And this ocean contains two to three times the amount of water on Earth.
And here’s the kicker: depending on the warmth of this ocean (which would come from Europa’s core and heating from Jupiter), it could potentially support life. And we’re not talking bacteria here. There is a legitimate possibility that Europa could support complex life.
[More information: 1. Europa: Overview, 2. Europa, Jupiter's Moon, Could Support Complex Life.]
2. Io - The Volcanic Hell World
Because of the enormous tidal friction from Jupiter, there is a lot of volcanic activity on Io. This moon is practically Mordor from the Lord of the Rings. In fact, the entire surface is covered with volcanoes. The eruptions are so frequent that Voyager took several photos which captured volcanoes mid-eruption (the dark red spots in the photo above). There are virtually no craters on Io because lava from the eruptions fills them and wipes the surface clean.
These volcanic eruptions can be seen from space:
And these eruptions have some kick to them too. Some rise as high as 190 miles and have half the velocity required to fling lava into space. Oh, and dibs on the band name “Space Lava.”
[More information: 1. Io: Overview, 2. Io (moon).]
1. Titan - Home Away From Home
Titan is, by far, the strangest moon in the solar system. It’s the only one with a dense atmosphere (one that is actually more dense than our own), and what lies beneath its thick clouds was a mystery for a very long time. Remarkably, Titan’s atmosphere is nitrogen-based, like Earth’s, but contains other gases such as methane. If the methane density is thick enough, it might rain liquid methane on Titan.
The existence of large, bright regions on its surface (that’s all we can really see through the clouds) imply that there are liquid seas on Titan’s surface which, given the type of rain, are probably methane as well. And because of the organic nature of most of these chemicals, it is possible that Titan too harbours life.
But far more exciting is the possibility of colonizing Titan in the future to harvest resources from Saturn. There will be many challenges involved, but everything necessary for human life is there: liquid water beneath the surface, gravity comparable to our own moon, and abundant fuel and fertilizer.
It may be a long way off, but Titan is one of our best chances for colonizing, strip mining, and polluting yet another body in the solar system.
[More information: 1. Titan: Overview, 2. Colonization of Titan.]
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