Some of you may remember a post I did awhile back declaring Europa to be my favorite moon. It’s a beautiful and mysterious world, a world that may have an incredible secret hidden beneath its icy crust. Europa frequently tops the list of most likely places where we might find alien life.
But as I’ve learned more about the Solar System, I’ve developed a deeper affection for another moon, one of Europa’s neighbors, a world that is neither beautiful nor likely to support life. I’m talking about Io.
Io is the innermost of Jupiter’s four big moons (Io, Europa, Ganymede, and Callisto). As such, it gets pushed and pulled around pretty hard. Between Jupiter’s enormous gravity and the combined gravitational forces of the other three Galilean moons, it’s enough pushing and pulling to make anyone queasy. And Io is a notoriously queasy planetoid.
Due to tidal forces, Io’s sulfur-rich interior is constantly boiling and churning. And Io keeps literally spewing out its guts, making it the most volcanically active object in the whole Solar System.
Like Venus, my favorite planet, Io is a great chemistry professor, especially when it comes to sulfur chemistry. Io’s also a pretty decent physics professor. While most of the sulfur from Io’s volcanic eruptions settles back onto the moon’s surface, plenty of it escapes into space. The result: crazy dangerous games of particle physics in the vicinity of Jupiter.
Io’s ionized sulfur has a lot to do with controlling the intense radio emissions coming from Jupiter. It’s also a major factor contributing to Jupiter’s insanely dangerous (to both humans and our technology) radiation environment. We recently learned that Jupiter has a third magnetic pole, located near the planet’s equator; while I haven’t read anything yet to back me up on this, I have a feeling Io is somehow responsible for that.
And lastly, Io’s ionized sulfur is partially (mainly?) responsible for the magnificent auroras that have been observed on Jupiter. And that’s my favorite bit about my favorite moon. I love the idea that Io—the ugliest ugly duckling in the Solar System—plays such a crucial role in creating something beautiful.
But of course picking a favorite anything is a purely subjective thing. Do you have a favorite moon? If so, what is it? Please share in the comments below!
Planet Pailly 
I’ve always liked Ganymede. Not entirely sure why! Probably the sheer size. I’ve thought for a long time it had potential for something in fiction. I have a page of notes about different worlds and moons in my fictional universe and put this for Ganymede…
Ganymede
One of the moons of Jupiter and in fact the largest moon in the Sol system, Ganymede is home to many industrial production facilities and spaceports specialising in bulk shipping. In an attempt to clean up the environment and reduce pollution levels much of Earth’s production and recycling was moved offworld to Ganymede. Earth is still home to many shipwrights and factories responsible for things the Central Earth Union deems important, but Ganymede is now responsible for the manufacture of clothing, tooling, chemical products and billions of everyday items.
‘Made on Ganymede’.
Many Merchant Fraternities that do not keep their business headquarters on Bellefonte instead maintain facilities on Ganymede.
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I think Ganymede and Callisto are prime targets for future colonization. Io is probably too hazardous, and I think Europa would probably get some sort of “national park” status in the future, especially if we do find life there.
I love the amount of thought you’ve put into your fictional universe. Are you using Ganymede as a setting for a specific story, or is this more of a world-building thing?
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That detail was more for world-building, possibly to be mentioned as a throwaway background fact. It won’t make it in as a setting (at least not in my current project but I hope to build a universe I can set many stories in).
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Cool! I want to do something similar with my work. Have a universe that can support lots of different stories, I mean.
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Being a fan of abstract art, I don’t find Io so ugly. Just a little bit 🙂
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That’s a nice way of thinking about it!
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2 Things. 1. Europa, Ganymede, and Callisto don’t look like they could hold Io so I guess 3.0 billion years later, Jupiter would win the gravitational tug-of-war. I don’t know how Callisto, Ganymede, and Europa are able to make such a strong gravity.
2. I once told you that Ganymede is my favorite moon and I told you why, but Ganymede has a downside. It’s downside is that Ganymede is too close too Europa, probably the second closest moon to Europa so maybe phobos would be my favorite moon in 2019.
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Wow, you must really hate Europa.
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As you might expect from our previous discusssions, my favorite is Saturn’s moon Iapetus. I talk about the view from Iapetus here: https://bkellysky.wordpress.com/2011/07/01/see-saturns-rings-from-saturns-moons/
But Io is cool. I love how the eruptions were discovered by a sharp-eyed engineer who was enhancing the photos of Io to look for background stars for navigation purposes!
Of course, I would rank our moon higher, just because from my perch here on Earth, I can see more detail on it than any other body in the solar system.
bob k
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The Moon is rather conveniently located for us Earth-based astronomers. I didn’t know that about Io. I thought the volcanoes weren’t discovered until Voyager 1 got there.
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Right- that was navigation for voyager, voyager 1 I think
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Oh okay. Yeah that makes sense.
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I’m sort of partial to Earth’s Moon, but I bet that doesn’t count. =) When you think about all the little subtle effects it has on us, light, migration patterns, etc as well as the cultural references to the Moon as representation of a night deity, and tides, weather… Earth and humankind would be very different without it!!
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I’d say the Moon counts. And you’re right, humanity would be very different without it. It’s possible humanity wouldn’t exist at all if not for the Moon’s gravity helping to stabilize Earth’s tilt!
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Triton is my favourite moon. I just find it pretty cool that it orbits retrograde around Neptune
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Triton is really awesome. And NASA may be sending a mission there in the next few years!
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That would be great if NASA goes ahead with that idea, would love to learn more about Triton along with my 2 fave planets
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Even thoughTriton is the moon that I like the most, I gotta admit I’ve gained a sorta fondness for Io, there’s just something about it that interests me 🤔
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Same. There’s really no place else in the Solar System quite like Io. Triton’s a pretty special moon too, though, with it’s retrograde orbit and cantaloupe terrain.
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