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Saturn's Moon Iapetus Has A 'Belt'
Believe writes "In another unexpected find by Cassini-Huygens, Saturn's moon Iapetus shows a bulging waistline. According to the story, the dark side of the moon is almost perfectly bisected by a tall, narrow ridge that runs for 1300 km (808 mi) and rises up to 20 km (12 mi) high. This height is amazing in such a small moon; it rivals Olympus Mons on Mars which is a body 5 times its size."
with that ridge on this pic : http://saturn.jpl.nasa.gov/multimedia/images/image -details.cfm?imageID=1270
it REALLY has a passing resemblance to a death star.
did anyone else notice this?
...I think it was had a story about a planet with a wall round the middle. (A long time ago now.) If there's any chance this wall has similar properties, we need to get a robot down there to take a look at it.
Panurge has posted for the last time. Thanks for the positive moderations.
It's a ridge on the planet surface, not a ring.
But I don't see why it is "amazing in such a small moon". Aren't larger irregularities to be expected with smaller bodies? For instance, the Mariana-Everest difference is about 19 km, so Earth's crust can be described crudely as "R0 +/- 9.5 km". Olympus Mons on Mars is at 26 km above surrounding ground. Comets are not even spherical - the "peaks" are as big as the rest of the "planet". So why is Iapetus's ridge considered surprising? I'm more interested in the ridge being *only* as tall as Olympus Mons, which is on a planet 5 times the size of Iapetus.
Time flies like an arrow. Fruit flies like a banana.
It is surprising in the way these mountains are on the moon's equator and form a nice belt.
That there is little erosion isn't a surprise, but the mountains origin is far more interesting.
On earth mountains are all results of our molten core (plate tektonics and vulcanoes). There must be some process that created this moutain belt.
Jeroen
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For several reasons:
On Earth mountains are caused by plate tectonics, i.e. disconnected area of crust floating on magma that run into each other, but such mechanism are impossible on small bodies because they cool too fast, i.e their crust quickly become too thick and form a single fused objet.
Of course mountains can also be volcanoes, but similarly this implies magma that can rise to the surface, i.e a crust that is not too thick.
The exception are moons close enough to their parent body so that internal heat can be sustained by tidal effects. This is the case on Io, for example.
However there can only be tidal effects if the moon is rotating around itself at a different rate as it revolves around its parent body. For Iapetus, just like our moon, the two rates are the same and they always present the same face to their parent. This implies only minimal tidal effects due to the eccentricity of the orbit.
Of course the mountain/volcano may have been formed a very long time ago when the moon wasn't as cool as it is now, probably this is the case for mount Olympus on Mars, however there is erosion on most planetary bodies even without atmosphere or low gravity, caused by the myriad of asteroid impact they sustain.
One remaining option is impact by a large asteroid. We now have to come up with a reasonable impact scenario that can produce a feature similar to the one seen on Iapetus, which is indeed very strange.
Thanks.
Stories like this make slashdot cool.
Does it go on forever?
Coincidences are weird, sometimes.
Kim Stanley Robinson is well known for his hard sci-fi Mars trilogy (Red Mars, Green Mars, Blue Mars). He has also written a small and memorable fantasy book, A Short, Sharp Shock, which takes place on a strange world covered by sea, almost perfectly bisected by a tall, narrow ridge that seems to run all around the world (but maybe only for 1300 km?) and that sometimes almost reaches the sea, sometimes climbs up to great heights (20 km maybe?).
Just a coincidence, of course, but it's funny that a man who loves space in general and planets in particular would use an existing but at the time unknown geological feature as the basis of a fantasy book.
I have two theories...
Less possible:
What I'd look for are two large craters of similar size and same age (can be estimated by amount of erosion from later meteorites), placed on opposite sides of the moon, shifted from the surface of the intersection by similar distance in opposite directions. Strong enough hit could have just split the moon it two...
More possible:
The moon had its own ring, just like Saturn has. But the ring's rotation was slowed down by Saturn's gravity (the same way our Moon's rotation got stopped by Earth) and the ring was pulled by the moon's gravity down, on the surface, depositing all the material straight below its orbit.
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Article submitter didn't take Astronomy 101 apparently. Small planetoids tend to have more prominent geological features than larger planets because stronger gravity pulls everything together harder and flattens things out. For instance, Olympus Mons on Mars is much higher than any mountain on Earth precisely because Earth has stronger gravity.
Why? There is a limit on which heights are possible for a given celestial body (planets etc., that is, I'm not counting in stars here), and that limit is actually higher for a smaller body (for example, a volcano the size (height) of Olympus Mons wouldn't even theoretically be possible on earth).
quidquid latine dictum sit altum videtur.
Tidal lock doesn't necessarily mean that the revolution of Iapetus is in the plane of the ring or Saturn's rotation (or is it so? I can't locate its ephemeris).
Actually Iapteus could orbit opposite to Saturn's location and perpendicular to the ring, it doesn't matter. What only matters is so its orbit axis was parell to its rotation axis when it had a normal daily cycle yet (no tilt), and paralell to its ring axis. (so tidal lock was changing speed, not direction of rotation). Nowadays when it's stopped it's impossible to tell.
Its gravitation field is not significant enough to trap a larger number of small bodies as Saturn does.
Sure it wouldn't if it was somewhere in open space. But in Saturn's ring it has enough debris nearby to catch them. Much lower strength but way more material to catch. And weak gravity isn't that much of a problem as most of the ring material travels at similar speed, very slowly, so obtaining a "high orbit" for a random piece of rock moving only slightly faster or slightly slower than the moon is really easy.
As they decend onto the surface, it'd make a crater, not mountains.
So they do. Great most of them. Only some that get onto its orbit get to create the ridge. They can keep orbiting for millenia (and get stabilized on the equatorial orbit from any randomness where they got) before they finally slowed down by gravity fall to the surface, and as Iapteus has no atmosphere, they can orbit an inch over the surface and still won't fall unless they hit something (horizontally), and rapidly losing speed fall somewhere more or less on vector of their orbit. You get a crater from a really powerful hit from straight above, when a fast moving body (be it accelerated by gravity or just floating through space at high speed) hits the surface. Not from a satellite of atmosphere-less planet, hitting the surface horizontally.
Anagram("United States of America") == "Dine out, taste a Mac, fries"
Anyone read Kim Stanley Robinson's [Red/Green/Blue] Mars?
Reminds me of the *big* space elevator cable that fell. If that caused lava flows/vulcanism in a line....
mark
i'm no scientist, but a couple of thoughts:
1: the ridge's length coincides very well with one axis of the extent of the dark material on the moon
2: (according to the article, i can only barely make this out myself) a large number of the craters have exposed clean ice only on the part of the rim that would be sheltered from anything coming from the equator. this includes the really big, old crater in the center of the picture, but also lots of newer ones.
3. *none* of the visible craters (as far as i can make out) have a clean basin, implying (to me) that the black material was laid down since the last significant impact on the moon; although, without wind, maybe most of the black material was just lifted straight up and fell right back down.
so, i would guess that the center ridge formed as a very odd volcanic eruption (or passing blow by a planet killing laser) which threw black material over half the moon. apparently this happened relatively recently, and not in conjunction with the large crater visible on the picture (though maybe with another newer one that isn't visible)