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Saturn’s Moon Wears the Weirdest Mountain Range in the Solar System

Of all the moons in the solar system, Iapetus has to be among the weirdest. Named after a spear-wielding Titan, the strange Saturnian satellite is less than half the size of Earth’s moon. But it’s a cluster of enigmas: Squished at its poles, the moon is walnut-shaped, has a face as black as coal and a bright white backside, and wears a big, spiky mountain range as a belt.

Even its orbit is weird: Iapetus is roughly three times farther from Saturn than its closest neighbor, Titan. And the path it takes around the planet is tilted, meaning it swings up and down as it orbits, rather than staying in the plane of Saturn’s rings like the rest of the “normal” satellites.

In other words, it’s kind of like the rebel of the Saturnian system, a moon who’d prefer to hang out behind the dumpster and cut class rather than play ball with the other kids.

Among the strangest of Iapetus’ unsolved mysteries is its super-chic, spiky mountain range. Running straight as an arrow along three-quarters of the moon’s equator, the thing is huge: Roughly 20 kilometers tall and up to 200 kilometers wide. (The peak of Mt. Everest, in comparison, rises only 8.85 kilometers above sea level.)

There’s nothing else like it in the solar system.

Close-up of the jagged ridge along Iapetus. (NASA/JPL/SSI)
Close-up of the jagged ridge along Iapetus. (NASA/JPL/SSI)

Scientists first spotted the ridge in 2004,  and since then, they’ve been trying to figure out how such a thing formed. Early theories suggested geologic activity within the moon itself – maybe something akin to Earth’s plate tectonics or volcanism had forced the ridge to rise up along the equator. But that didn’t make a lot of sense. The moon’s crust wasn’t spongy when the ridge formed, the evidence for active geology tepid.

Then, scientists thought maybe the ridge had formed as a result of the moon’s rotation period abruptly slowing down. Some early simulations suggest a day on the moon used to last for a mere 16 hours. Now, though, a day on Iapetus lasts 79 Earth-days – the same amount of time it takes the little guy to shuffle once around Saturn (the moon is tidally locked, meaning it’s plowing through space with the same face forward, always).

Maybe, teams said, a giant impact had knocked Iapetus into its current rotation state, and the resulting braking action caused the crust to buckle.

But most of these theories also predict other strange geologic features (which aren’t observed), or hinge upon the crust being a certain thickness (which it may not be).

In 2010, a new theory emerged. Perhaps the ridge is the remains of a former moon – a moon-moon, suggested Andrew Dombard of the University of Illinois at a meeting of the American Geophysical Union. Sometime during the evolution of the Saturnian system, he said, Iapetus may have had a little friend, roughly 100 kilometers in diameter. Whether the moon captured the moonlet, or the moonlet formed from the debris ejected by a giant impact (this is how Earth’s moon formed) isn’t known.

But eventually, that little friend wandered too close to cranky Iapetus and ended up being shredded by the planet’s gravity.

As the moonlet broke up, Dombard said, its pieces formed an ephemeral ring around Iapetus’ equator. The ring eventually rained down upon the satellite and deposited the giant ridge.

In 2011, another team suggested something similar, this time with a giant impact forming both a ring and a moonlet. The ring would go on to form the mountain range, while the moonlet would smash into Iapetus and create one of its many large impact basins.

Recent evidence, gleaned from the shape of the mountain ridge itself (steep and triangular), suggests that pieces falling from on high could make total sense. It’s kind of the same shape you get when you take a handful of sand and slowly sprinkle it into a pile.

Why the ridge only runs along three-quarters of the equator isn’t explained by this scenario, though.

In short, we still don’t know how Iapetus grew its monstrous mountains. But the idea of a moon with a moon, or a moon with a ring, is strangely compelling. Too bad Iapetus had to go and tear its little friend to bits.

The remains of a moonlet? (NASA/ESA/SSI)
The remains of a moonlet? (NASA/ESA/SSI)

85 thoughts on “Saturn’s Moon Wears the Weirdest Mountain Range in the Solar System

  1. Sorry, but you lost me after a few paragraphs Nadia.

    I’m afraid that the sentence “…it’s kind of like the rebel in the Saturnian system, a moon who’d prefer to hang out behind the dumpster and cut class rather than play ball with the other kids” just strikes me as very dumbed down and teenage. It’s not even easy to understand. What for example is a dumpster? It’s not a word we use in the UK and I’m sure other nations don’t use it.

    And “super-chic, spiky mountain range?” Come on!

    I’m afraid your style of writing is very poor and I certainly don’t think it’s professional. I’m even wondering whether you’re a youngster on work experience? Your writing style does give that ‘texting to my friends’ type of approach. It certainly doesn’t reflect well on an august and respected journal like National Geographic.

  2. Did someone say moon moon? http://knowyourmeme.com/memes/moon-moon

    Now I’m imagining Iapetus being circled by some derpy little friend who can’t even figure out how to moon properly.

    (P.S. to the previous commenter: This is a free-access science blog with casual posts about fun science stuff, not a heavily-edited copy of an “august” journal; a blog isn’t necessarily any less blog-y just because it is hosted on NatGeo’s website. If you don’t like this author’s casual writing style, just pick another blog until you find one that appeals… or stick to your actual science journals.)

  3. “Dumbster” is common to US and Australia. So other nations do use it. If you don’t know the word – google it or yahoo it (usually works for me). After all UK English and US English have numerous differences.

    As for the language and style used, I can’t really comment: I’m not competent in this field. But I did understand what it’s about and learned new things and in the end that’s what is important for me.

    Great article, by the way.

  4. Lighten up Andrew. It is a science related blog, not a science journal. A dry and technical writing style is going to fail in a mission to make science more accessible to the masses. As for word choices like “dumpster,” it is a widely understood noun in the USA and can be looked up. There are many nouns in English that are not common among the many English speaking cultures – it is interesting to discover the differences.
    To Nadia: Keep up the good work. I like the colorful language and metaphors in the many science blogs I read. Those that keep it dry and technical (or full of jargon) can be off-putting to even an intelligent, science educated nerd like me.

  5. wow, andrew, the world doesn’t revolve around england. perhaps you should start your own UK Geographic…

  6. Nadia, don’t mind cranky Andrew’s little rant. An interesting piece and nothing wrong with color commentary to bring some humor to the subject. Don’t let the sourpusses get you down.

  7. ^^^Don’t listen to Andrew, Nadia. I enjoyed the article immensely.
    Andrew, not everybody likes to sound pretentious, and some people like to have a giggle when reading.

    I never even thought about moons having satellites of their own, and I find that fascinating. I would love to see a video modeling some of these theories to the ridge.

  8. @Andrew

    The word “dumpster” is just another term for a large garbage bin and is quite commonly used here in North America.

  9. Completely disagree, Andrew. You are being a curmudgeon.

    Nadia’s writing style is fresh and modern. It’s a similar tone to many of the popular online magazines; Slate, Salon, Huffington Post.

    There’s nothing wrong with Nadia’s style, but there’s something very wrong with your literary tastes.

  10. After reading through the article, which I enjoyed, it occurred to me that the mountain range could have been formed while passing through an outer debris field [ring] early on when it was first captured by the planet. That long line makes me think of a probability curve when looking at the profile of the mountains.

  11. Andrew, dumpster is used in America. The sentence pretty much is just stating colorfully that the moon is a bit of an outcast that doesn’t follow the social norms, if that helps.

  12. I’m English and I know what a dumpster is. I love the idea of the moon having “a little friend”. Sounds so cute!

  13. Interesting article. I will say Andrew has a right to his opinion, I’m sure Nadia can take the criticism. I will be honest I kind of thought the same thing when I read that dumpster line. But other than that it was fascinating to learn about Saturn’s quirky little moon.

  14. It’s wonderful to be able to a get a peek at the controversies and consequent studies that are being generated as we explore space. The editorial position that National Geographic values is making science very accessible to those of us who aren’t scientists but who have a lot of curiosity about new discoveries, many of which would be hopelessly obscured by the very technical language and formulae in published studies. This article is a case in point. Thank You National Geographic and its writers.

  15. I love the solar system and I love the moons and other celestial bodies close to our planet, and I love the article, it is interesting and gives me a topic to talk about with my friends when looking at the stars in a clear summer night. That’s very nice of Nadia to share her Iapetus Article with us! I am also grateful 🙂

  16. Great article Nadia, not boring or too starched collar. I enjoyed it and learned something new. Please don’t let people like Andrew get under your skin. As you can see we all enjoyed your commentary. There is always one rotten apple in the barrel and in this case it’s Andrew. Keep up the great work.

  17. Andrew, you have made possibly the most British comment ever. A dumpster is like a skip, btw (sorry, I don’t mean to offend you with my initializations…) by the way.

  18. What is so difficult to understand?
    Just use your imagination if its blurry and it’ll make perfect sense.

  19. Comments like those posted by Andrew always say so much more about those who post them than those they are aimed at. Such is our digital age.

  20. On behalf of the good people of the UK: I know what a dumpster is; Nadia’s writing is elegant, evocative, and refreshing; and we’re not all condescending pillocks.

  21. I looks like something that has been molded, thus suggesting that it may have been 2 separate entities. It also suggests that the cores of the originating objects were very attractive and had flexible outer skins. The impact of their combination leads to the altered path, but also making it a possible that heating occurred during impact and that the impact was not “high speed”.

  22. Also note, it also can explain why the ridge only circumnavigates 3/4 of the satellite, since trajectory comes into play with all aforementioned events.

  23. There are inconsistencies between your article and that in Wikipedia. The Wikipedia article states the ridge is 1300 km long on a moon whose diameter at the equator is 1492 km. This calculates to 28% of the circumference of the moon. The Wikipedia article does mention short segments of ridge and individual peaks elsewhere along the equator. It also mentioned incomplete photo coverage of the moon so some parts of the possible ridge may lack coverage.

    Looking at the first image in your article, the 28% of circumference is reasonably compatible as the ridge continuity breaks up near the center of the photo and I can’t follow it into the crater at right. Perhaps your greater length includes the parts that include isolated peaks and shorter segments.

    The profile of the ridge on the closeup where it is projected against the black of space shows a side slope around 27º to 35º, allowing for the slightly off-equatorial view. This is compatible with a granular material as you suggest in your ring-hypothesis for origin of the ridge if the material properties of ice at that temperature are similar to those of sand. The limited lengths of the ridge segments might mean the orbiting ring was composed of several small loosely aggregated bodies that had a skimming collision at slow relative velocity so they formed the ridges rather than having enough energy to splatter their particles after impact. The Wikipedia article mentioned an area of three closely spaced parallel ridges. Perhaps a loosely aggregated satellite broke up due to gravitation effects (like the comet that hit Jupiter) and the ridges were formed by the disintegration of the pieces on a single pass. The gaps in the ridge being simple between where the individual pieces struck. This avoids the problem of how a ring that gradually built up the ridge would have gaps. It does not explain the solitary peaks, however so this cannot be a complete explanation. Lacking access to the actual photos, my speculations are poorly founded.

  24. As an experienced physicist (in general), I do agreee that this mountain range looks like the outcome of the collapse of an old ring of debris. This idea should be contrasted with the frequency of impacts over the moon, as the number of craters seems to be quite regular over all the surface, including the mountain range. Good article. You got a new follower 😉

  25. It is surprising to note how meaningless fillers such as like, kind of, I don’t know etc. have become acceptable in colloquial American English. It is not a very promising trend to be introduced in written English as well. The information in the article was interesting, though.

  26. finally something I can read to my 8 and 13 year old grand kids without having to explain half the words. I really enjoyed it

  27. Who cares about grammar. The important thing is the shape of the moon, the size, the orbit and the possibility of a moon orbiting another moon. I have my own opinion as to how it was formed. I haven’t worked out all the details, but am getting close. Thank you for the thought provoking article.

  28. Glad we could all keep this on subject. i usually don’t comment, however I’m rather confused still. its not the article or how it was written that bothers me, its how this moon is able to travel in a different direction than the rest, and why one side is always dark and how was thd debris sprinkled in a line on the equator only?

    But if were gonna keep this article off subject, it har really inspired me to paint a titan nutcracker half black half white wielding a spear accompanied by his midget squire

  29. A sort of gigantic additive manufacturing technique ? Could this ring been sort of 3d printed…with debris… Love this blog please continue !!!! Don’t mind the form… It’s te content that matters. 🙂

  30. I think the writer’s enthusiasm really came through in the article and although informal styles are not for everyone I thought it was despite that very well written.

  31. Good to see a gradual swing to the moon being the winner on the day. I just love learning about these things being discovered, seen as quirky at first but perhaps in the fullness of time become common place and ordinary. Here a mini moon Iapetus possibly commited infanticide on its own micro/proto moon. Planets with moons with moons, reminds me of the debate when I was a child about whether the earth was unique. Without any evidence beyond a rudimentary understanding of the solar system and moons orbiting planets it seemed reasonable to me that what we observed was ordinary, that planets orbited stars. In my opinion I thought it would be more difficult to find stars that don’t have satellites rather than stars that do. Keep me enthralled, keep these articles comming, in any prose you choose. OK one caveat, please refrain from saying really, such as in really hot etc.

  32. Well I’m from the UK and I know what a dumpster is, we do have them here too, I guess Andrew has led a very sheltered life raised on Encyclopaedia Britannica.

    I found the article refreshing and liked the analogy myself I can just imagine Iapetus wearing a leather jacket with his collar up and his studded leather belt, just one of the cool kids on the block.

  33. What Ed Yong said, but also on behalf of miserable old gits in the UK like myself. Your blog posts are interesting, intelligent and witty. Keep writing.

  34. How fun would it be if Andrew was Nadia? :p

    great article, I probably wouldn’t have read it if it was just another science journal, since I’m just a curious person, not a scholar.

  35. It alarms me how quickly ‘people’ are ready to put others down, what is wrong with you, a little encouragement wouldn’t go a miss. Congratulations to the writer of this piece we thoroughly enjoyed it in fact it was interesting and an enjoyable read Thank you !

  36. might it have been possible for this small moon to have been hit by a very large, slower moving chunk of space debris? the moon is described as walnut shaped…so a powerful direct hit might be the answer…it might have compressed the moon 75% around its equator, forcing internal collapse and the resultant ridge pushed up 16 miles…

  37. Good article. I just wish there was less comments about Andrew and more on the subject.
    I believe the theory of rotation may come into play. If it was spinning fast for a number of million years at the equator it would be spinning faster at the poles and it could rise. The inertia at the equator could raise up the surface. If you take a wet ball and spin it you will find that all the water will flow to the “equator” and spin of of the ball at that point.
    That is my final answer.

  38. The word that I was trying to remember in my first comment and use was centrifugal force. Everything traveling wants to travel in a straight line. Thus the mountains forming over a long period of time at the area of the stronger force.

  39. It is too bad that the first comment in this list is so negative and attacks the author. Good interpretive writing includes metaphors. This author is a great interpretive writer. She makes the subject easily understood and enables readers to make connections, which is what interpretive writing is all about.
    Perhaps Andrew (that first critical commenter), should take a course in interpretive writing….

  40. Andrew, should Nadia submit any future articles to you first for editing prior to publishing? Perhaps you could share one of the articles that you’ve written with Nadia & the rest of us.
    Im sure everyone will be grateful to read something that is of the highest standard rather than being “dumbed down”…….or contain crazy words like “dumpster” in it.

    Nadia – thanks for the great read. Looking forward to reading more of your work soon.

  41. I hope to continue learning everything I can from your delightful blog, Nadia. Love your work. Thank you for sharing with us.

    Best wishes

  42. From an age 73 female, found the article informative, with a great light touch and fun. Could easily picture a smash up with debris raining down in a straight line on a spinning body.

  43. Great article, very enlightening in a light-hearted fashion about a body in our solar system with which I knew very little, other than it’s different colour faces.
    Fascinating, and it’s encouraged me to want to follow this blog in future.
    And as an Englishman who hits 60 next month, I’m perfectly conversant with the term ‘dumpster’, and the concept of ‘dumpster-diving’.
    Perhaps Andrew should read more SF, like William Gibson, as it was in Neuromancer twenty-odd years ago I think I first came across the term.
    He should perhaps lighten up a little as well, he could get an ulcer otherwise…

  44. Andrew – Just. Go. Home. As a professional writer myself, I found her writing style refreshing. It’s called having a “writer’s voice.”

    Nadia — Ignore the cranky old man who wrote that stupid comment. And now that you’ve found your writer’s voice, don’t lose it!

  45. did anybody see the piramid shape in the lower middle of the ridge in the first picture? maybe its just coincidence.

  46. I absolutely loved the article and the style in which it was written. That said, I wonder if it could be the remnants of a failed ring around Saturn?! If it happened a long time ago when the moon was not tidally locked it could have just plowed through the old ring until there was nothing left to deposit on it. That would explain why it only went part way around.
    Another explanation could be that when the moon was still not completely hardened it could have been impacted at the pole and simply squished the moon together and the ridge was pushed out like the mountains here where two tectonic plates collide and form a mountain range. Even here, The mountain ranges vary in their height and length!

    Anyways, don’t let the comments of an old fuddy duddy ruin your article, I enjoyed the comparison and had a bit of a chuckle at your descriptions.
    Keep up the good work!!!

  47. A mountain range that size can only mean that the core wants to be on the outside. It will fall apart soon

  48. Iapetus is the Saturn’s moon chosen by Arthur C. Clarke (2001 Space Odyssey) to serve as a base for the monolith. The reasons behind the choice are justly those strange things on its surface.

  49. You can give up all your guessing, its an artificial satellite actually the death star from star wars. case closed.

  50. Most of you have missed the obvious here. The ridge in question is simply the injection molding line, and this is a meteorite damaged giant gumball, delivered from the well documented Cosmic Vending System.

  51. Band-aid is to plaster like dumpster is to skip or pound to quid. Could go on forever. Who cares! Great article!!

  52. Enhance your vocabulary andrew, it’ s so narrow. a kindergarten could understand a dumpster..good job Nadia!

  53. Nadia, great piece…discovery should be fun, light hearted, accessible! People should be able to get a taste and then decide to further foray into the nuts and bolts of something in more detail…dry, technical, and all the trappings. I too echo the others: keep up the great work!

  54. Not sure if it is possible, but could a larger object have been drawn i while on a similar trajectory, so while on impact it it created what we see today and maybe why the range does not run the whole way round, not sure if that it would work that way?

    And I hope we can keep on track, great article but the Trolling effect worked.

  55. I enjoyed your article, Nadia. I was also very pleased with the photos. Here is my analysis, for what it is worth. I have a suspicion that Iapetus is an artificial moon. I think it was constructed; and likely an earlier attempt at such a satellite than our moon. The object in question has an obvious ‘weld’ putting the two pieces of the walnut together. If you look at the surface photos, the thing looks organic. The craters do not appear to be impact sites, especially when you look at Iapetus in the first photo, the thing looks like some kind of metallic structure. When we examine some metallic thing we have made, under a powerful microscope, we see that the surface is not smooth either, but a pock marked place with disturbed surfaces akin to these moons of ours. Jupiter has such a moon also; it also keeps one face constantly looking down at the host planet. We have to keep in mind, we are very puny beings. There are beings living in the universe who are very huge in comparison to us. We humans are but insects compared to the giant races who have been flying hither and thither for eons before this planet was born.

  56. Another example of u.s. writing standards going down the drain.
    It would be nice if someone with a background in at least amateur astronomy wrote about this subject instead of someone that sounds like they are tweeting on a cell phone.

    ND: Hi, Alice. You and Andrew and entitled to your criticisms and opinions, but please try to stay on topic and keep criticism constructive. Personal attacks and comments showing disrespect to other commenters or myself will no longer be tolerated. To everyone else: Thank you for your support! I appreciate it and am glad you enjoyed the story. Iapetus is one of my favorite objects in the solar system. — nadia

  57. Add another name to the list of people who think that “Andrew” is out of his mind. Enjoyed the article; love the blog.

    Science rules.

  58. As once stated in a most popular movie franchise..

    “That’s not a moon, it’s a space station.”

  59. Iapetus is just the Greek form of Japheth who was one of the Biblical Noah’s sons. The strange mountain ridge was probably the result of an impact or hit with another satellite. There was a war in the heavens in ancient times. The Bible describes the slaying of ‘Tiamat’ when rebel angel forces were defeated and a planet between Mars and Jupiter was destroyed resulting in the current asteroid chain.

  60. Nadia, You’re beautiful, intelligent, inquisitive and a good science writer. I have no idea where Andrew is coming from.

    This mountain range is very interesting. ‘Roughly 20 kilometers’ in height. That’s not the Ozarks, Smokies are even the Rockies. This is a massive range.

    None of the theories proposed make any sense, but the one that makes the most sense is the one that was rejected at the very beginning — geologic processes.

    Debris raining down from orbit, I think, would leave a gouge and craters instead of a mountain range.

    Anyway, if you ever want to go on a hike there, invite me along.

  61. Interesting piece, Nadia. Thank you for bringing this astronomical anomaly to my attention. Has anyone considered the possibility that Iapetus may be artificial–a construct? Phobos shows signs of artificiality; even Luna has odd longitudinal banding which suggests construction (as well as strangely hollow seismic readings). Whatever cataclysm blew up Planet Five (Phaeton) long ago damaged and deranged much of the Solar System. Mars was once habitable; Venus may have been, too.

  62. I agree with Russ that Iapetus is an artificial satellite and so is our moon. Does the large circular crater not remind you of the ‘death star’ of Star Wars fame…some people know things we mere mortals are not privy too!

  63. Here, link below, is an even better site about Iapetus! It is more weird than just having this very odd mountain range. It is a Web Site of seven very long pages – but is totally interesting reading. Try it, you’ll like it! Page One starts here and each page has a link to the next.



  64. Whoa! †нªηкs a great deal †̥o every σηє including the critics…as some σηє once said, “critics are our friends, they make us know our shortcomings”.

    I share the view of Stephen Proper and Mark Riley. Additionally,the leather-like outer surface of this moon could suggest a hot interior… that makes it not fragile enough †̥o have broken into pieces by whatever might have bashed it out of shape and, perhaps, plane. Its awkward swing up and down could testify †̥o the fact that it is it is still out of balance. All †̥ђε same, †нªηк s †̥o Nadia for giving us this ‘big bone †̥o chew on. Pls Nadia what’s U̶̲̥̅̊я twter handle?

  65. Nice article, easy to understand, fun to read. I never knew about this moon and now I can take away quite a few things that are easy to remember. So that’s a win!

    Ignore the negative comments because those that can’t do, criticize!

  66. Interesting article. Could this be the proof of intelligent life in the universe we have been looking for?

    (ND: Alas, no.)

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