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Astronomers Solve Puzzle of the Mountains That Fell From Space
KentuckyFC (1144503) writes "Iapetus, Saturn's third largest moon, was first photographed by the Cassini spacecraft on 31 December 2004. The images created something of a stir. Clearly visible was a narrow, steep ridge of mountains that stretch almost halfway around the moon's equator. The question that has since puzzled astronomers is how this mountain range got there. Now evidence is mounting that this mountain range is not the result of tectonic or volcanic activity, like mountain ranges on other planets. Instead, astronomers are increasingly convinced that this mountain range fell from space. The latest evidence is a study of the shape of the mountains using 3-D images generated from Cassini data. They show that the angle of the mountainsides is close to the angle of repose, that's the greatest angle that a granular material can form before it landslides. That's not proof but it certainly consistent with this exotic formation theory. So how might this have happened?
Astronomers think that early in its life, Iapetus must have been hit by another moon, sending huge volumes of ejecta into orbit. Some of this condensed into a new moon that escaped into space. However, the rest formed an unstable ring that gradually spiraled in towards the moon, eventually depositing the material in a narrow ridge around the equator. Cassini's next encounter with Iapetus will be in 2015 which should give astronomers another chance to study the strangest mountain range in the Solar System."
Astronomers think that early in its life, Iapetus must have been hit by another moon, sending huge volumes of ejecta into orbit. Some of this condensed into a new moon that escaped into space. However, the rest formed an unstable ring that gradually spiraled in towards the moon, eventually depositing the material in a narrow ridge around the equator. Cassini's next encounter with Iapetus will be in 2015 which should give astronomers another chance to study the strangest mountain range in the Solar System."
Iapetus has only a fraction of Earth's gravity (Iapetus radius 735 KM, Earth radius 6371 KM, you do the math, after figuring out the relative density for yourself). Wouldn't a hugely smaller gravity significantly affect the angle of repose they carry on about in that referenced scientific paper? I doubt you can compare the angle of repose of rounded particles (or snow and hail) on Earth with that of a very small _and airless!_ moon.
But I'll leave that to the astrophysicists to work out.
From the references in that exact article you criticize (but clearly didn't read):
"Kleinhans, M. G., Markies, H., de Vet, S. J., in 't Veld, A. C., Postema, F. N., 2011. Static and dynamic angles of repose in loose granular materials under reduced gravity. Journal of Geophysical Research 116, E11004."
So, yes, I'd say they did take into account the low gravity.
Astrophysicists my ass... Geologists have this covered! From "Static and dynamic angles of repose in loose granular materials under reduced gravity"
http://adsabs.harvard.edu/abs/...
Until now it has been assumed that the angles of repose are independent of gravitational acceleration. The objective of this work is to experimentally determine whether the angles of repose depend on gravity. In 33 parabolic flights in a well-controlled research aircraft we recorded avalanching granular materials in rotating drums at effective gravitational accelerations of 0.1, 0.38 and 1.0 times the terrestrial value. The granular materials varied in particle size and rounding and had air or water as interstitial fluid. Materials with angular grains had time-averaged angles of about 40 degrees and with rounded grains about 25 degrees for all effective gravitational accelerations, except the finest glass beads in air, which was explained by static electricity. For all materials, the static angle of repose increases about 5 degrees with reduced gravity, whereas the dynamic angle decreases with about 10 degrees. Consequently, the avalanche size increases with reduced gravity.
Yes it's an anecdote! Were you expecting original research in a Slashdot comment?
It is generally accepted that planetary ring systems are not stable, permanent features but are a result of collisions, gravitational disintegration, or other disruption of an existing satellite. The rings, over time, will eventually re-form into a new satellite, or be lost to space or to the parent object. So there is really no such thing as an 'original ring system'.
Does not sound like they solved it. Headline should be "Astronomers Ponder Puzzle..." perhaps?
No, it should be, "Astronomers Increase Plausibility of Exotic Formation for Iapetus Mountain Range".
"Proof" is not something science does. Nor does it do "disproof", despite Karl Popper's well-marketed myth of method.
Science is the discipline of publicly testing ideas by systematic observation, controlled experiment and Bayesian inference, and the only thing Bayesian inference can ever do is increase or decrease the plausibility of some proposition or propositions. Plausibilities range between epsilon and omega = 1 - epsilon (0 and 1 are epistemic errors, the term for which is "faith").
So in this case they have done more than "pondering the puzzle": they have contributed to knowledge (which is by its nature uncertain) by increasing the plausibility of the proposition that these mountains "fell from space".
Blasphemy is a human right. Blasphemophobia kills.
Yes, Iapetus was photographed by Voyager 2 in 1981 (link to NASA image with metadata listed), and I would suspect that there were earth based images taken well before that (but none that would show any detail).
Who would have expected a summary on Slashdot to be carelessly wrong about something factual and easily verified?
just a ghost in the machine.
New year's eve 2004 was the first time that Cassini imaged Iapetus. At least that was how I read the sentence.
"Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
Saturn's ring material falling onto the Iapetus. This "mountain range" is technically an equatorial ridge, but as anyone who's seen an hour glass it's not hard to imagine (-- disclaimer) the same thing is happening on the moon of a planet with it's own ring system.
No. In that theory, the satellites interior to Iapetus, i.e., Mimas, Enceladas,Tethys, Dione, Rhea and (maybe) Titan would all have similar equatorial ridges, which they do not.
Till we see 1300km long and 10 to 10 km diameter asteroids in space, we just have to file it under, "it is the best we could do, under these circumstances".
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
See a doctor.
systemd is Roko's Basilisk.
No its not, the article talks about the idea that a collision with another body both caused the inclined orbit of Lapetus, and created enough ejected materials to form a unstable ring system that fell back to the surface, causing the fancy walnut shaped moon we all know and love. The article is more about how they gathered and interpreted the data that re-enforces this hypothesis. If saturn where solid, I'm sure it would have a similar mountain range, or at least an equatorial band of impact craters from parts of its ring system that have fallen over the millennia.
I've decided to Diversify my Holdings. I've divided my cash between my left and right pockets, instead of all in one.
Exactly, this article essentially is an elaboration on the Wiki Article's theory # 3.
They make much of the angle of repose, but the angle of repose is not a constant. Gravity of the planet/moon affects this angle, (which I am sure they accounted for), but so does the water content, or any other potentially binding agent (frozen CO2, etc) of the material. Even the shape of the grains of sand can affect the Angle of Repose.
Sig Battery depleted. Reverting to safe mode.