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Old 04-22-2014, 07:01 PM
 
Location: Maine
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If a civilization were advanced enough to have permanent colonies on the moon --- and that is an extremely unproven IF --- then I doubt piddly things like meteors would trouble them much. They probably use the eluduium Q38 space modulator to repel the meteors.
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Old 04-25-2014, 02:26 PM
 
Location: Philadelphia
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Quote:
Originally Posted by Terryj View Post
That's HAL, I guess you never saw the movie 2001 A Space Odyssey
Somewhat off-topic, but has anyone ever heard of the mysterious Toynbee Tiles in Philadelphia and other cities around the World? Pretty fascinating stuff and related to 2001 A Space Odyssey. There are hundreds of these.

Toynbee tiles - Wikipedia, the free encyclopedia

Mystery of tiles on city streets solved in Philadelphia documentary

Resurrect Dead: The Mystery of the Toynbee Tiles (2011) - IMDb


Last edited by 2e1m5a; 04-25-2014 at 02:35 PM..
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Old 04-26-2014, 09:19 AM
 
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Quote:
Originally Posted by 303Guy View Post
Thanks. I got the idea of earth sorta shielding the moon from when Shoemaker-Levi 9 hit Jupiter. It was being said that Jupiter attracted incoming debris which sorta protected earth. I assumed it would have been to a lesser extent. What a scientist said about the earth shielding the moon is that it would be to the extent of some 3 square minutes of arc worth IIRC. Not a helluva lot. And I had forgotten about the lava flows on the near side of the moon and didn't know the lunar crust was thinner on the near side side. So thank you for for enlightening me. I'm still amazed by the 33 tonnes per day!

And that recent meteoroid hit was from the May meteorite shower stream. Interesting meteorite impact pattern on the moon.

http://science.nasa.gov/media/medial...mpacts_med.jpg
Jupiter is too far to do any direct shielding. But its gravitational pull on objects passing close enough to (1)alter the path of the object, (2) rip apart objects that are too close, but not close enough to be pulled in, or (3) pull objects right into it. In the case of the Shoemaker-Levi 9 comet, it was close enough to be ripped apart into fragments as it head in the direction of the Sun, and on its return smacked into Jupiter. The alignments of both Jupiter and the comet, as well as the comet's trajectory of the comet, were just right for the impacts to happen. In a sense, Jupiter does sort of provide some degree of protection, but it can also be chaotic in terms of sending debris in all sorts of directions. It an object is coming into the solar system far from Jupiter, the the gas giant would have no effect on such an object. Jupiter's orbit is a long way out from the Sun. Even though Jupiter's gravitational field in extremely strong, there's a staggering amount of space in relation to its orbit that the planet would have no effect on objects approaching far from it.

The orbits of the planets are somewhat on a disc plane, but there are far more objects that can come in from above the disk and below it. The Oort Cloud is spherical and a source for the origin for lomg-period comets that can come in from any direction. These objects are probably set into motion by disturbances from passing stars and maybe rogue planets passing by or even through the Cloud. Comets can originate from the Kuiper Belt as well (more aligned with the Solar System's plane) but is thought to produce very few comets. At a guess, Kuiper Belt comets are probably set into motion by collisions with other objects in the Belt.
Oort cloud - Wikipedia, the free encyclopedia

By the way, in the photo of the far side of the Moon, you can see a series of craters in the lower half (center) of the Moon. It's possible these may have been formed fromed by a chain of meteor fragments that collided one after the other. It's an interesting pattern.

Quote:
Originally Posted by 303Guy View Post
And this is the explanation to what the monks saw in 1178 AD

http://spaceflightnow.com/news/n0104/19bruno/
I would agree with that as the most likely explanation. The Giordano Bruno crater notion just doesn't hold up for the reasons given.
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Old 04-29-2014, 11:57 PM
 
Location: Auckland, New Zealand
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Interesting. OK, so I did a little research on Shoemaker-Levi 9. It was a comet orbiting Jupiter when it was discovered. Apparently it had been capered by Jupiter some twenty nine years earlier. It broke up in 1992 when it passed real close to Jupiter, it having a highly elliptical orbit which made it unstable when it came under the sun's gravity. Anyway, what was said is that Jupiter has far more comet and asteroid impacts than earth and that it 'sweeps up' the asteroids. On the other hand it's Jupiter that pulls asteroids out of stable orbit and into earth's way in the first place!
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Old 04-30-2014, 11:20 AM
 
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Originally Posted by 303Guy View Post
Anyway, what was said is that Jupiter has far more comet and asteroid impacts than earth and that it 'sweeps up' the asteroids. On the other hand it's Jupiter that pulls asteroids out of stable orbit and into earth's way in the first place!
Yes, I'd say impacts occurs more frequently on Jupiter that Earth given its enormous size and gravitational pull. Still, it requires the colliding objects to be within Jupiter's range. I suppose Jupiter does affect asteroids to some degree. Asteroids in the Belt are more subject to occasional crashing into each other which can alter trajectories into any direction. In the past when the Asteroid Belt was more populated with protoplanets, Jupiter had more affect on the objects. While there is still a relatively significant population in the Belt, overall it seems to be pretty sparse between objects. Even so, over long historical periods of time, there are enough objects to pose various degrees of potential collision with the Earth.

Jupiter's gravitational effect could effect asteroids such as the Trojans and Greeks, and to some degree the Hildas. The Trojans and the Greek camp trail behind and in front of Jupiter. I'm not sure Jupiter actually passes through them. These might be failed protoplanets that never actually formed like Ceres and Vesta. The main body of the Asteroid Belt seems to far from Jupiter though, other than occasional strays that get too close to the gas giant. Those could just as easily be hurled out in the direction of Saturn as in the direction of the Earth. Uncontrolled Gravitational Assist (Gravitational Slingshot) is a factor and hard to say at what point an object would be set free.
Asteroid belt - Wikipedia, the free encyclopedia
File:InnerSolarSystem-en.png - Wikipedia, the free encyclopedia
Gravity assist - Wikipedia, the free encyclopedia

Regarding comets, most seem to be from either the Kuiper Belt or the Oort Cloud, both of which are too far to be disturbed by Jupiter. Where Jupiter can affect comets is when one swings by close enough to Jupiter's gravitational field. Comets from the Oort Cloud can come in from any direction without coming anywhere near Jupiter. If one does pass near Jupiter, then it could potentially be affected. Oort Cloud comets are thought to be disturbed by stars that are close enough in passing as the solar system orbits the galaxy. Comets are pretty fascinating objects.

That's not to say that there's no gravitational effect at great distances, just that at a certain point the gravitational field becomes so weak that there's very little effect. I'm reminded of the idea several decades ago, the Jupiter Effect, that a number of the outer planets were going to be aligned in a way spelling doomsday for the Earth. Needless to say, nothing happened and we're still here.
The Jupiter Effect - Wikipedia, the free encyclopedia
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Old 04-30-2014, 11:34 PM
 
Location: Auckland, New Zealand
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Thanks, NightBazaar. Fascinating! One day I am going to try to understand the gravitational slingshot effect. That Wiki link on the asteroid belt is very interesting. I did know a little about the three clusters of asteroids in harmonic sinc with Jupiter but that image is quite revealing. Great stuff! Thank you.
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