by neufer » Sun Aug 09, 2009 2:26 pm
http://en.wikipedia.org/wiki/Iapetus_(mythology) wrote:
<<In Hesiod's Works and Days Prometheus is addressed as "son of Iapetus", and no mother is named. However, in Hesiod's Theogony, Klymene is listed as Iapetus' wife and the mother of Prometheus. In Horace's Odes, in Ode 1.3 Horace describes how "audax Iapeti genus/ Ignem fraude mala gentibus intulit"; "The bold offspring of Iapetus [i.e. Prometheus]/ brought fire to peoples by wicked deceit".>>
------------------------------------------
http://apod.nasa.gov/apod/ap090809.html wrote:
Explanation: What has happened to Saturn's moon Iapetus? Vast sections of this strange world are dark as coal, while others are as bright as ice. The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon. Iapetus also has an unusual equatorial ridge that makes it appear like a walnut. To help better understand this seemingly painted moon, NASA directed the robotic Cassini spacecraft orbiting Saturn to swoop within 2,000 kilometers in 2007. Pictured above, from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is always trailing. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater of similar size. The dark material is seen increasingly coating the easternmost part of Iapetus, darkening craters and highlands alike. Close inspection indicates that the dark coating typically faces the moon's equator and is less than a meter thick. A leading hypothesis is that the dark material is mostly dirt leftover when relatively warm but dirty ice sublimates. An initial coating of dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons. This and other images from Cassini's Iapetus flyby are being studied for even greater clues.
------------------------------------------
http://apod.nasa.gov/apod/ap060103.html wrote:
Explanation: Why are vast sections of Iapetus as dark as coal? No one knows for sure. Iapetus, the third largest moon of Saturn, was inspected again as the Saturn-orbiting robot Cassini spacecraft swooped past the enigmatic world again late last year. The dark material covers most of the surface visible in the above image, while the small portion near the top that appears almost white is of a color and reflectance more typical of Saturn's other moons. The unknown material covers about half of the 1,500 kilometer wide moon. The material is so dark that it reflects less than five percent of incident sunlight, yet overlays craters indicating that it was spread after the craters were formed.
Iapetus has other unexplained features. The bright part of Iapetus is covered with unexplained long thin streaks. The orbit of Iapetus is also unusual, being tilted to the plane of Saturn's orbit by an unusually high fifteen degrees. A strange ridge about 13 kilometers high crosses much of Iapetus near the equator and is visible near the bottom. Oddly, this ridge is almost exactly parallel with Iapetus' equator. The exact shape of Iapetus remains undetermined, but images indicate that it is quite strange -- something like a walnut. Research into the formation and history of mysterious Iapetus is active and ongoing.
http://antwrp.gsfc.nasa.gov/apod/ap070919.html
http://antwrp.gsfc.nasa.gov/apod/ap070915.html
------------------------------------------
http://antwrp.gsfc.nasa.gov/apod/ap070914.html
------------------------------------------
http://en.wikipedia.org/wiki/Iapetus_(moon) wrote:
<<Iapetus was discovered by Giovanni Domenico Cassini in October 1671 on the western side of Saturn. Then Cassini tried unsuccessfully to observe it on the eastern side of the planet in early 1672. This pattern continued as Cassini observed Iapetus in December 1672 and February 1673, each time tracking it for a fortnight on the western side of Saturn, but he was unable to detect it during the intervening period, when it should have been on the eastern side. Cassini finally observed Iapetus on the eastern side in 1705 with an improved telescope, finding it two magnitudes dimmer on that side.
Cassini correctly surmised that Iapetus has a bright hemisphere and a dark hemisphere, and that it is tidally locked, always keeping the same face towards Saturn, so that the bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and the dark hemisphere on the other side. The dark hemisphere was later named Cassini Regio in his honour.
NASA scientists now believe that the dark material may be lag (residue) from the sublimation (evaporation) of water ice on the surface of Iapetus, possibly darkened further upon exposure to sunlight. Because of its slow rotation of 79 days (equal to its revolution and the longest in the Saturnian system), Iapetus likely had the warmest daytime surface temperature and coldest nighttime temperature in the Saturnian system even before the development of the color contrast; near the equator, heat absorption by the dark material results in a daytime temperatures of 128 K in the dark Cassini Regio compared to 113 K in the bright regions. The difference in temperature means that ice preferentially sublimates from Cassini, and precipitates in the bright areas and especially at the even colder poles. Over geologic time scales, this would further darken Cassini Regio and brighten the rest of Iapetus, with all exposed ice being lost from Cassini, creating a thermal positive feedback for ever greater contrast in albedo. It is estimated that, at current temperatures, over one thousand million years Cassini would lose about 20 meters of ice to sublimation, while the bright regions would lose only 10 centimeters, not considering the ice transferred from the dark regions. This model explains the distribution of light and dark areas, the absence of shades of grey, and the thinness of the dark material covering Cassini.
However, a separate process of color segregation would be required to get the thermal feedback started. The initial dark material is thought to have been debris blasted by meteors off small outer moons in retrograde orbits and swept up by the leading hemisphere of Iapetus. The core of this model is some 30 years old, and has been revived by the September flyby.
Light debris outside of Iapetus's orbit, either knocked free from the surface of a moon by micrometeoroid impacts or created in a collision, would spiral in as its orbit decays. It would have been darkened by exposure to sunlight. A portion of any such material that crossed Iapetus's orbit would have been swept up by its leading hemisphere, potentially coating it to create a contrast in albedo, and so a contrast in temperature, that could have been exaggerated by the thermal feedback described above.
The largest reservoir of such material is Phoebe, the largest of the outer moons. Although Phoebe's composition is closer to that of the bright hemisphere of Iapetus than the dark one, dust from Phoebe would only be needed to establish a contrast in albedo, and presumably would have been largely obscured by later sublimation.>>
------------------------------------------
- Edward Everett Hale » The Brick Moon (1869)
<<For you see that if, by good luck, there were a ring like Saturn's which stretched round the world, above Greenwich and the meridian of Greenwich, and if it would stay above Greenwich, turning with the world, any one who wanted to measure his longitude or distance from Greenwich would look out of window and see how high this ring was above his horizon. At Greenwich it would be over his head exactly. At New Orleans, which is quarter round the world from Greenwich, it would be just in his horizon. A little west of New Orleans you would begin to look for the other half of the ring on the west instead of the east; and if you went a little west of the Feejee Islands the ring would be over your head again. So if we only had a ring like that, not round the equator of the world,--as Saturn's ring is around Saturn,--but vertical to the plane of the equator, as the brass ring of an artificial globe goes, only far higher in proportion,-- "from that ring," said Q., pensively, "we could calculate the longitude."
Failing that, after various propositions, he suggested the Brick Moon. The plan was this: If from the surface of the earth, by a gigantic peashooter, you could shoot a pea upward from Greenwich, aimed northward as well as upward; if you drove it so fast and far that when its power of ascent was exhausted, and it began to fall, it should clear the earth, and pass outside the North Pole; if you had given it sufficient power to get it half round the earth without touching, that pea would clear the earth forever. It would continue to rotate above the North Pole, above the Feejee Island place, above the South Pole and Greenwich, forever, with the impulse with which it had first cleared our atmosphere and attraction. If only we could see that pea as it revolved in that convenient orbit, then we could measure the longitude from that, as soon as we knew how high the orbit was, as well as if it were the ring of Saturn.
"But a pea is so small!"
"Yes," said Q., "but we must make a large pea."
...
Why we settled on two hundred feet of diameter I hardly know... four thousand miles is a good way off to see a moon even two hundred feet in diameter.
Small though we made them on paper, these two- hundred-foot moons were still too much for us. Of course we meant to build them hollow. But even if hollow there must be some thickness, and the quantity of brick would at best be enormous. Then, to get them up! The pea- shooter, of course, was only an illustration.
Q. again suggested the method of shooting oft the moon. It was not to be by any of your sudden explosions. It was to be done as all great things are done,--by the gradual and silent accumulation of power. You all know that a flywheel--heavy, very heavy on the circumference, light, very light within it--was made to save up power, from the time when it was produced to the time when it was wanted. Yes? Then, before we began even to build the moon, before we even began to make the brick, we would build two gigantic fly-wheels, the diameter of each should be "ever so great," the circumference heavy beyond all precedent, and thundering strong, so that no temptation might burst it. They should revolve, their edges nearly touching, in opposite directions, for years, if it were necessary, to accumulate power, driven by some waterfall now wasted to the world. One should be a little heavier than the other. When the Brick Moon was finished, and all was ready, IT should be gently rolled down a gigantic groove provided for it, till it lighted on the edge of both wheels at the same instant. Of course it would not rest there, not the ten-thousandth part of a second. It would be snapped upward, as a drop of water from a grindstone. Upward and upward; but the heavier wheel would have deflected it a little from the vertical. Upward and northward it would rise, therefore, till it had passed the axis of the world. It would, of course, feel the world's attraction all the time, which would bend its flight gently, but still it would leave the world more and more behind. Upward still, but now southward, till it had traversed more than one hundred and eighty degrees of a circle. Little resistance, indeed, after it had cleared the forty or fifty miles of visible atmosphere. "Now let it fall," said Q., inspired with the vision. "Let it fall, and the sooner the better! The curve it is now on will forever clear the world; and over the meridian of that lonely waterfall,--if only we have rightly adjusted the gigantic flies,--will forever revolve, in its obedient orbit, the--
I was to spend the winter in one final effort to get twenty-five thousand dollars more if I could, with which we might paint the MOON, or put on some ground felspathic granite dust, in a sort of paste, which in its hot flight through the air might fuse into a white enamel. All of us who saw the MOON were so delighted with its success that we felt sure "the friends" would not pause about this trifle.>>
---------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Iapetus_(mythology)"]
<<In Hesiod's Works and Days Prometheus is addressed as "son of Iapetus", and no mother is named. However, in Hesiod's Theogony, Klymene is listed as Iapetus' wife and the mother of Prometheus. In Horace's Odes, in Ode 1.3 Horace describes how "audax Iapeti genus/ Ignem fraude mala gentibus intulit"; "The bold offspring of Iapetus [i.e. Prometheus]/ brought fire to peoples by wicked deceit".>>[/quote]------------------------------------------
[quote=" http://apod.nasa.gov/apod/ap090809.html"]
Explanation: What has happened to Saturn's moon Iapetus? Vast sections of this strange world are dark as coal, while others are as bright as ice. The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon. Iapetus also has an unusual equatorial ridge that makes it appear like a walnut. To help better understand this seemingly painted moon, NASA directed the robotic Cassini spacecraft orbiting Saturn to swoop within 2,000 kilometers in 2007. Pictured above, from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is always trailing. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater of similar size. The dark material is seen increasingly coating the easternmost part of Iapetus, darkening craters and highlands alike. Close inspection indicates that the dark coating typically faces the moon's equator and is less than a meter thick. A leading hypothesis is that the dark material is mostly dirt leftover when relatively warm but dirty ice sublimates. An initial coating of dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons. This and other images from Cassini's Iapetus flyby are being studied for even greater clues. [/quote]------------------------------------------
[quote=" http://apod.nasa.gov/apod/ap060103.html"]
Explanation: Why are vast sections of Iapetus as dark as coal? No one knows for sure. Iapetus, the third largest moon of Saturn, was inspected again as the Saturn-orbiting robot Cassini spacecraft swooped past the enigmatic world again late last year. The dark material covers most of the surface visible in the above image, while the small portion near the top that appears almost white is of a color and reflectance more typical of Saturn's other moons. The unknown material covers about half of the 1,500 kilometer wide moon. The material is so dark that it reflects less than five percent of incident sunlight, yet overlays craters indicating that it was spread after the craters were formed.
Iapetus has other unexplained features. The bright part of Iapetus is covered with unexplained long thin streaks. The orbit of Iapetus is also unusual, being tilted to the plane of Saturn's orbit by an unusually high fifteen degrees. A strange ridge about 13 kilometers high crosses much of Iapetus near the equator and is visible near the bottom. Oddly, this ridge is almost exactly parallel with Iapetus' equator. The exact shape of Iapetus remains undetermined, but images indicate that it is quite strange -- something like a walnut. Research into the formation and history of mysterious Iapetus is active and ongoing.
[b] http://antwrp.gsfc.nasa.gov/apod/ap070919.html
http://antwrp.gsfc.nasa.gov/apod/ap070915.html[/b][/quote]------------------------------------------
[b] http://antwrp.gsfc.nasa.gov/apod/ap070914.html[/b]
------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Iapetus_(moon)"]
<<Iapetus was discovered by Giovanni Domenico Cassini in October 1671 on the western side of Saturn. Then Cassini tried unsuccessfully to observe it on the eastern side of the planet in early 1672. This pattern continued as Cassini observed Iapetus in December 1672 and February 1673, each time tracking it for a fortnight on the western side of Saturn, but he was unable to detect it during the intervening period, when it should have been on the eastern side. Cassini finally observed Iapetus on the eastern side in 1705 with an improved telescope, finding it two magnitudes dimmer on that side.
Cassini correctly surmised that Iapetus has a bright hemisphere and a dark hemisphere, and that it is tidally locked, always keeping the same face towards Saturn, so that the bright hemisphere is visible from Earth when Iapetus is on the western side of Saturn, and the dark hemisphere on the other side. The dark hemisphere was later named Cassini Regio in his honour.
NASA scientists now believe that the dark material may be lag (residue) from the sublimation (evaporation) of water ice on the surface of Iapetus, possibly darkened further upon exposure to sunlight. Because of its slow rotation of 79 days (equal to its revolution and the longest in the Saturnian system), Iapetus likely had the warmest daytime surface temperature and coldest nighttime temperature in the Saturnian system even before the development of the color contrast; near the equator, heat absorption by the dark material results in a daytime temperatures of 128 K in the dark Cassini Regio compared to 113 K in the bright regions. The difference in temperature means that ice preferentially sublimates from Cassini, and precipitates in the bright areas and especially at the even colder poles. Over geologic time scales, this would further darken Cassini Regio and brighten the rest of Iapetus, with all exposed ice being lost from Cassini, creating a thermal positive feedback for ever greater contrast in albedo. It is estimated that, at current temperatures, over one thousand million years Cassini would lose about 20 meters of ice to sublimation, while the bright regions would lose only 10 centimeters, not considering the ice transferred from the dark regions. This model explains the distribution of light and dark areas, the absence of shades of grey, and the thinness of the dark material covering Cassini.
However, a separate process of color segregation would be required to get the thermal feedback started. The initial dark material is thought to have been debris blasted by meteors off small outer moons in retrograde orbits and swept up by the leading hemisphere of Iapetus. The core of this model is some 30 years old, and has been revived by the September flyby.
Light debris outside of Iapetus's orbit, either knocked free from the surface of a moon by micrometeoroid impacts or created in a collision, would spiral in as its orbit decays. It would have been darkened by exposure to sunlight. A portion of any such material that crossed Iapetus's orbit would have been swept up by its leading hemisphere, potentially coating it to create a contrast in albedo, and so a contrast in temperature, that could have been exaggerated by the thermal feedback described above.
The largest reservoir of such material is Phoebe, the largest of the outer moons. Although Phoebe's composition is closer to that of the bright hemisphere of Iapetus than the dark one, dust from Phoebe would only be needed to establish a contrast in albedo, and presumably would have been largely obscured by later sublimation.>>[/quote]------------------------------------------
[list][list][b]Edward Everett Hale » The Brick Moon (1869) [/b][/list]
<<For you see that if, by good luck, there were a ring like Saturn's which stretched round the world, above Greenwich and the meridian of Greenwich, and if it would stay above Greenwich, turning with the world, any one who wanted to measure his longitude or distance from Greenwich would look out of window and see how high this ring was above his horizon. At Greenwich it would be over his head exactly. At New Orleans, which is quarter round the world from Greenwich, it would be just in his horizon. A little west of New Orleans you would begin to look for the other half of the ring on the west instead of the east; and if you went a little west of the Feejee Islands the ring would be over your head again. So if we only had a ring like that, not round the equator of the world,--as Saturn's ring is around Saturn,--but vertical to the plane of the equator, as the brass ring of an artificial globe goes, only far higher in proportion,-- "from that ring," said Q., pensively, "we could calculate the longitude."
Failing that, after various propositions, he suggested the Brick Moon. The plan was this: If from the surface of the earth, by a gigantic peashooter, you could shoot a pea upward from Greenwich, aimed northward as well as upward; if you drove it so fast and far that when its power of ascent was exhausted, and it began to fall, it should clear the earth, and pass outside the North Pole; if you had given it sufficient power to get it half round the earth without touching, that pea would clear the earth forever. It would continue to rotate above the North Pole, above the Feejee Island place, above the South Pole and Greenwich, forever, with the impulse with which it had first cleared our atmosphere and attraction. If only we could see that pea as it revolved in that convenient orbit, then we could measure the longitude from that, as soon as we knew how high the orbit was, as well as if it were the ring of Saturn.
"But a pea is so small!"
"Yes," said Q., "but we must make a large pea."
...
Why we settled on two hundred feet of diameter I hardly know... four thousand miles is a good way off to see a moon even two hundred feet in diameter.
Small though we made them on paper, these two- hundred-foot moons were still too much for us. Of course we meant to build them hollow. But even if hollow there must be some thickness, and the quantity of brick would at best be enormous. Then, to get them up! The pea- shooter, of course, was only an illustration.
Q. again suggested the method of shooting oft the moon. It was not to be by any of your sudden explosions. It was to be done as all great things are done,--by the gradual and silent accumulation of power. You all know that a flywheel--heavy, very heavy on the circumference, light, very light within it--was made to save up power, from the time when it was produced to the time when it was wanted. Yes? Then, before we began even to build the moon, before we even began to make the brick, we would build two gigantic fly-wheels, the diameter of each should be "ever so great," the circumference heavy beyond all precedent, and thundering strong, so that no temptation might burst it. They should revolve, their edges nearly touching, in opposite directions, for years, if it were necessary, to accumulate power, driven by some waterfall now wasted to the world. One should be a little heavier than the other. When the Brick Moon was finished, and all was ready, IT should be gently rolled down a gigantic groove provided for it, till it lighted on the edge of both wheels at the same instant. Of course it would not rest there, not the ten-thousandth part of a second. It would be snapped upward, as a drop of water from a grindstone. Upward and upward; but the heavier wheel would have deflected it a little from the vertical. Upward and northward it would rise, therefore, till it had passed the axis of the world. It would, of course, feel the world's attraction all the time, which would bend its flight gently, but still it would leave the world more and more behind. Upward still, but now southward, till it had traversed more than one hundred and eighty degrees of a circle. Little resistance, indeed, after it had cleared the forty or fifty miles of visible atmosphere. "Now let it fall," said Q., inspired with the vision. "Let it fall, and the sooner the better! The curve it is now on will forever clear the world; and over the meridian of that lonely waterfall,--if only we have rightly adjusted the gigantic flies,--will forever revolve, in its obedient orbit, the--
[b]I was to spend the winter in one final effort to get twenty-five thousand dollars more if I could, with which we might paint the MOON, or put on some ground felspathic granite dust, in a sort of paste, which in its hot flight through the air might fuse into a white enamel. All of us who saw the MOON were so delighted with its success that we felt sure "the friends" would not pause about this trifle.[/b]>>
---------------------------------------------------[/list]