67P, why erosion from the neck?

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Re: 67P, why erosion from the neck?

Unread postby jacmac » Thu Dec 18, 2014 6:35 pm

CC said:
Now let's look at it from the frame of reference of the IPM. As the comet plows through the solar wind, charges in the IPM are separated by that friction on the leading side of the comet. After the the comet has passed, those charges can recombine. This gives the appearance of a tail following the comet wherever it goes,


So, what is going on when the comet goes around the sun and the "tail" is leading the way ?
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Re: 67P, why erosion from the neck?

Unread postby viscount aero » Thu Dec 18, 2014 6:40 pm

CharlesChandler wrote:Hey Folks,

In my comet model, there are a total of 4 layers of alternating charge (2 positive and 2 negative). The charge separation mechanism is frictional charging from the comet moving through the interplanetary medium (IPM). When the comet is going against the solar wind, the charging is the most robust. As is always the case when a solid object moves through a gas/plasma, a boundary layer of gas/plasma builds up on the leading side of the object. If the velocity of the object is supersonic, this transforms into a detached bow shock, and the boundary layer gets bigger with increasing velocity, contrary to the subsonic regime, in which the boundary layer gets compressed with increasing velocity. The reason for the detached bow shock is that as the comet moves through the IPM, neutral atoms in the IPM impinging on the boundary layer have their electrons stripped off, and the atomic nuclei get embedded in the boundary layer deeper than the electrons, due to the greater mass of the +ions. This creates a halo around the comet, with a layer of stripped electrons left around the outside, and a layer of +ions on the inside, up against the comet. Electrostatic repulsion between the +ions is what bloats the boundary layer out into the detached bow shock. The other 2 layers of charge are inside the comet itself. The +ions in the comet's atmosphere induce a negative charge on its surface, and that induces a positive charge in its core.

So that's the model from the cometary frame of reference. Now let's look at it from the frame of reference of the IPM. As the comet plows through the solar wind, charges in the IPM are separated by that friction on the leading side of the comet. After the the comet has passed, those charges can recombine. This gives the appearance of a tail following the comet wherever it goes, and suggests that the tail (i.e., the coma) is comprised of particles that were eroded from the comet. But that would be a truly enormous amount of erosion going on, and it's a bit hard to believe that there would be much left of the comet after just one trip through the inner solar system. Then it becomes impossible to explain regularly recurring events such as Halley's Comet, whose orbital period should change dramatically with the mass loss, since lighter objects have lower terminal velocities, encountering more friction per mass than large objects. But if the coma is actually just particles in the IPM that are recombining after the comet has passed, there isn't any mass loss. It's like watching a motorboat zip across a lake. If we think that the wake is comprised of particles stripped off of the motorboat, and if we estimate the amount of mass involved, we'd be hard-pressed to explain why there would be anything left of the motorboat by the time it got to the far shore. But if the wake is just the effect that the motorboat had on the medium, there isn't any mass loss. Also note that in the case of a supersonic detached bow shock, the friction actually goes down instead of up with increasing velocity. Below the speed of sound, the drag force increases with the cube of the velocity, but above the speed of sound, the drag force actually relaxes. This is because the object gets surrounded by a teardrop-shaped envelope of gas/plasma that eliminates the vacuum on the leeward side of the object, which is the primary retarding force.

If comets are surrounded by plasma sheaths that insulate them from the solar wind, it becomes possible to understand how dust could accumulate on their surfaces. Dust doesn't generally last very long in high winds, and one would think that supersonic winds would sweep the surface quite clean. But if the impinging winds never actually get close to the surface, dust can accumulate. We can also understand why jets emanating from the interior of the comet don't show the effects of the supersonic speed. If you rigged up something to release a gas from the nose cone of a commercial airliner, in flight at 400 mph you'd see the gas getting swept back by the onslaught of air through which the plane is flying. You wouldn't see the gas expand away from the plane unaffected by the ambient atmosphere. Thus the behavior of cometary jets proves that they are expanding into a sheath that surrounds the comet, which insulates it from the solar wind.

So why do comets sometimes break up, especially when they get near to large objects, such as planets, or the Sun? This is typically attributed to gravitational forces. But the effect of gravity should be extremely slight compared to stresses from the drag force. Analogously, anything not bolted firmly to an airplane has a tendency to get torn off at flight speed, not because of differential gravity, but because of the drag force incurred by the airplane moving rapidly through the atmosphere. OK, so what if there isn't any drag force, because the supersonic object is encased in a protective sheath? Then the forces in that sheath are the ones to look at. And if the interior of the comet is positively charged, the Coulomb force will be pressing outward, so that's the likeliest force responsible for cometary break-ups. It's also the force that would drive jets emanating from the surface. If there is internal pressure due to the Coulomb force, but if the comet's crust is still strong enough to hold the whole thing together, the pressure will be relieved by jets. Once away from the surface, the positively charged jets will be attracted to the negatively charged outer layer of the detached bow shock. So the jets will expand conically away from the comet, and will be made visible from charge recombination.

Now -- back to the original topic -- what is the nature of the corrosion on the comet's surface? I don't know, and I'm going to defer to Viscount Aero (et al.)'s analysis of the chemistry. If the surface was positively charged, I'd say that it was just the positive charge that was liberating atoms by removing the covalent bonding. So whichever chemicals had the lowest ionization potentials would be the first to go, leaving stronger bonds in place, producing selective corrosion, and possible pitting of the surface. If the surface is negatively charged, it wouldn't seem to have this problem. But then again, when exposed to the unfiltered light from the Sun, photo-ionization might make the day side of the comet positively charged, with the night side picking up an equal-but-opposite negative charge.

Why don't comets get eroded spherically, as we otherwise would expect, and hence the topic of this thread? I don't know. ;)


I want to address some of this later but why are you assuming the jets come from within the comet when there is no evidence for that?
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Re: 67P, why erosion from the neck?

Unread postby CharlesChandler » Thu Dec 18, 2014 8:40 pm

jacmac wrote:So, what is going on when the comet goes around the sun and the "tail" is leading the way ?

The coma traces the path of the comet through the solar wind, which is a lot faster than the comet itself. Then there can be multiple tails, which I consider to be proof that the coma is electrically charged, and thus the components of it can go in different directions, depending on the electrical environment in the IPM.

viscount aero wrote:...why are you assuming the jets come from within the comet when there is no evidence for that?

Well, perhaps we should open that up. You're introducing the possibility that the jets could be going the other way -- particles streaming inward? And/or it's a discharge that is just moving electrons through a static atmosphere? But yes, I was just assuming that they are streams away from the comet. ;)

http://science.nasa.gov/science-news/sc ... settajets/
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Re: 67P, why erosion from the neck?

Unread postby viscount aero » Fri Dec 19, 2014 12:18 am

CharlesChandler wrote:
jacmac wrote:So, what is going on when the comet goes around the sun and the "tail" is leading the way ?

The coma traces the path of the comet through the solar wind, which is a lot faster than the comet itself. Then there can be multiple tails, which I consider to be proof that the coma is electrically charged, and thus the components of it can go in different directions, depending on the electrical environment in the IPM.

viscount aero wrote:...why are you assuming the jets come from within the comet when there is no evidence for that?

Well, perhaps we should open that up. You're introducing the possibility that the jets could be going the other way -- particles streaming inward? And/or it's a discharge that is just moving electrons through a static atmosphere? But yes, I was just assuming that they are streams away from the comet. ;)

http://science.nasa.gov/science-news/sc ... settajets/
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That isn't what you implied. Of course particles stream outward. But you said this:

"We can also understand why jets emanating from the interior of the comet don't show the effects of the supersonic speed."

Interior of the comet?
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Re: 67P, why erosion from the neck?

Unread postby CharlesChandler » Fri Dec 19, 2014 12:46 am

viscount aero wrote:That isn't what you implied. Of course particles stream outward. But you said this:

"We can also understand why jets emanating from the interior of the comet don't show the effects of the supersonic speed."

Interior of the comet?

Oh, OK. Yes, I was assuming that the particles come from the interior, and no, I don't think that there is any evidence of that. It could be particles just from the surface. Also, I'm not 100% satisfied with my characterization of the jets as conical charge streams, since they seem to be more collimated than conical. Hmmm...
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Re: 67P, why erosion from the neck?

Unread postby viscount aero » Fri Dec 19, 2014 1:17 am

CharlesChandler wrote:Hey Folks,

In my comet model, there are a total of 4 layers of alternating charge (2 positive and 2 negative). The charge separation mechanism is frictional charging from the comet moving through the interplanetary medium (IPM). When the comet is going against the solar wind, the charging is the most robust. As is always the case when a solid object moves through a gas/plasma, a boundary layer of gas/plasma builds up on the leading side of the object. If the velocity of the object is supersonic, this transforms into a detached bow shock, and the boundary layer gets bigger with increasing velocity, contrary to the subsonic regime, in which the boundary layer gets compressed with increasing velocity.

Hence, sonic booms with supersonic aircraft.

CharlesChandler wrote:The reason for the detached bow shock is that as the comet moves through the IPM, neutral atoms in the IPM impinging on the boundary layer have their electrons stripped off, and the atomic nuclei get embedded in the boundary layer deeper than the electrons, due to the greater mass of the +ions. This creates a halo around the comet, with a layer of stripped electrons left around the outside, and a layer of +ions on the inside, up against the comet. Electrostatic repulsion between the +ions is what bloats the boundary layer out into the detached bow shock.


So you mean the + ions in the comet's atmosphere (coma) repel the + [heavier] ions in the bow shock, hence the standing off of the bow shock, detached.

CharlesChandler wrote:The other 2 layers of charge are inside the comet itself. The +ions in the comet's atmosphere induce a negative charge on its surface, and that induces a positive charge in its core.


What do you mean by "core"? What if a comet has no core? What if the comet is just a piece of shattered debris?

CharlesChandler wrote:So that's the model from the cometary frame of reference. Now let's look at it from the frame of reference of the IPM. As the comet plows through the solar wind, charges in the IPM are separated by that friction on the leading side of the comet. After the the comet has passed, those charges can recombine. This gives the appearance of a tail following the comet wherever it goes, and suggests that the tail (i.e., the coma) is comprised of particles that were eroded from the comet.


Seems like a mixed bag. Yes the tail is an ionized debris field from the cometary body. But the tail doesn't follow the comet outbound from the Sun; the tail leads the comet outbound. The coma and the tail(s) are different structures. The coma is an atmosphere, a spherical structure. The tails are diffuse debris streams. Because the tails change position relative to the Sun upon perihelion indicates the Solar atmosphere (or region of directed plasma/radiation) is blowing the tails out.

This is why I think, along with most EU consensus, that there is no "interior jetting" happening. The jetting is all happening on the outside of the comet, from its surface. It must be this way because:

• The comet is a rotating body on an axis, yet the tail remains pointed in one direction--not following the axial rotation of the comet. In other words, the tail is independent of the axial rotation of the comet. This is evidence that the jetting is not coming from the interior of the comet but originates on the outside of the comet
• No physical vents, structures, holes, caves, cracks, are ever seen on a comet's surface where the jetting is coming from.
• Locations of the jetting change perpetually (to my knowledge).
• For the solar wind to affect the tails, causing the tails to LEAD the comet on its outbound trajectory, the "jetting" must be coming from the surface.
• Were jetting coming from the interior of the comet, the jetting would be coming from fixed locations, spiraling the ejecta around the comet as it rotates about an axis. But this is not observed.

CharlesChandler wrote:But that would be a truly enormous amount of erosion going on, and it's a bit hard to believe that there would be much left of the comet after just one trip through the inner solar system. Then it becomes impossible to explain regularly recurring events such as Halley's Comet, whose orbital period should change dramatically with the mass loss, since lighter objects have lower terminal velocities, encountering more friction per mass than large objects.


Yes and this is why they invented the Oort Cloud. The Oort Cloud is a bandaid to get around this problem (mostly). They so badly want comets to be multi-billion-year old ancient building blocks that magically "seed the oceans of the Earth and icy moons". But per the "erosion" problem, they can't visit the Sun very often before they are totally eaten away or break apart. So they invented the "Oort Cloud" as a vast "holding pen" where some mysterious dark forces dislodge the occasional comet--sent on to the Sun--to resupply the comet stream and explain away the erosion problem. Halley's Comet was only "recently perturbed" from the "Oort Cloud" and sent to the Sun. Halley's Comet is alleged to be "4 billon years old" but has only "recently" visited the Sun.

CharlesChandler wrote:But if the coma is actually just particles in the IPM that are recombining after the comet has passed, there isn't any mass loss. It's like watching a motorboat zip across a lake. If we think that the wake is comprised of particles stripped off of the motorboat, and if we estimate the amount of mass involved, we'd be hard-pressed to explain why there would be anything left of the motorboat by the time it got to the far shore. But if the wake is just the effect that the motorboat had on the medium, there isn't any mass loss. Also note that in the case of a supersonic detached bow shock, the friction actually goes down instead of up with increasing velocity. Below the speed of sound, the drag force increases with the cube of the velocity, but above the speed of sound, the drag force actually relaxes. This is because the object gets surrounded by a teardrop-shaped envelope of gas/plasma that eliminates the vacuum on the leeward side of the object, which is the primary retarding force.


This is interesting as it describes the matter in the comas and tails simply "falling back down" onto the comet, albeit onto a modified surface (the developing peanut shape over time). This nullifies any notion of a comet being eroded or corroded away. The streaming mass/particles just reconfigure themselves back onto the etched comet body in a recycling process. This is an interesting idea.

This may be happening. To wit, on the outward bound path, the tails that LEAD the comet eventually dissipate the farther away from the Sun the comet gets. Being ahead of the comet, the dust and debris just collides back onto the comet as the tails lose structure farther away from the Sun's intensity.

CharlesChandler wrote:If comets are surrounded by plasma sheaths that insulate them from the solar wind, it becomes possible to understand how dust could accumulate on their surfaces. Dust doesn't generally last very long in high winds, and one would think that supersonic winds would sweep the surface quite clean. But if the impinging winds never actually get close to the surface, dust can accumulate.


I don't quite follow this when you say: "But if the impinging winds never actually get close to the surface, dust can accumulate."

As I described above, the outward bound dust tails that lead the comet just collide (recombine) with the comet as the comet gets farther and farther away from the intensity of the Sun. Any mass loss is recaptured again and again and again.... The comet recycles itself per your model. I like this idea even though it may not be true. It could be very viable.

CharlesChandler wrote:We can also understand why jets emanating from the interior of the comet don't show the effects of the supersonic speed.


Again there is no evidence for jets coming from the interior.
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Re: 67P, why erosion from the neck?

Unread postby viscount aero » Fri Dec 19, 2014 1:30 am

CharlesChandler wrote:If you rigged up something to release a gas from the nose cone of a commercial airliner, in flight at 400 mph you'd see the gas getting swept back by the onslaught of air through which the plane is flying. You wouldn't see the gas expand away from the plane unaffected by the ambient atmosphere. Thus the behavior of cometary jets proves that they are expanding into a sheath that surrounds the comet, which insulates it from the solar wind.


I follow this concept and like how you described it. However, again, the solar wind causes the tails to LEAD comet on the outward bound trajectory. Therefore the solar wind (or nearest intensity of radiation) directly affects the way the tails behave. The tails are not immune or necessarily isolated in a bubble. However this may not preclude the existence of a sheath :)

CharlesChandler wrote:So why do comets sometimes break up, especially when they get near to large objects, such as planets, or the Sun? This is typically attributed to gravitational forces. But the effect of gravity should be extremely slight compared to stresses from the drag force.


Yes agree.

CharlesChandler wrote: Analogously, anything not bolted firmly to an airplane has a tendency to get torn off at flight speed, not because of differential gravity, but because of the drag force incurred by the airplane moving rapidly through the atmosphere. OK, so what if there isn't any drag force, because the supersonic object is encased in a protective sheath? Then the forces in that sheath are the ones to look at. And if the interior of the comet is positively charged, the Coulomb force will be pressing outward, so that's the likeliest force responsible for cometary break-ups.


I believe you posited this idea about the Chelyabinsk bolide, ie, Coulomb force.

CharlesChandler wrote: It's also the force that would drive jets emanating from the surface. If there is internal pressure due to the Coulomb force, but if the comet's crust is still strong enough to hold the whole thing together, the pressure will be relieved by jets.


For me this places too much faith in a "core" and "interior" whereas I believe the comet is homogenous, like slag. There is no outer "crust", fixed jets, nor internal "geysers" happening on a comet in my opinion. Same with a bolide. A bolide is a chunk of rock.

CharlesChandler wrote:Once away from the surface, the positively charged jets will be attracted to the negatively charged outer layer of the detached bow shock. So the jets will expand conically away from the comet, and will be made visible from charge recombination.


Dunno. Don't follow.

CharlesChandler wrote:Now -- back to the original topic -- what is the nature of the corrosion on the comet's surface? I don't know, and I'm going to defer to Viscount Aero (et al.)'s analysis of the chemistry. If the surface was positively charged, I'd say that it was just the positive charge that was liberating atoms by removing the covalent bonding. So whichever chemicals had the lowest ionization potentials would be the first to go, leaving stronger bonds in place, producing selective corrosion, and possible pitting of the surface. If the surface is negatively charged, it wouldn't seem to have this problem. But then again, when exposed to the unfiltered light from the Sun, photo-ionization might make the day side of the comet positively charged, with the night side picking up an equal-but-opposite negative charge.

Why don't comets get eroded spherically, as we otherwise would expect, and hence the topic of this thread? I don't know. ;)


I must finish my first draft and let you read it :) Likewise, I like your ideas, Charles. The comet MAY be in a sheath actually. I like that. Always a good read from you.
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Re: 67P, why erosion from the neck?

Unread postby Metryq » Fri Dec 19, 2014 2:44 am

Maol has already compared comets to magnets. If that is so, would the nucleus become two magnets upon fissioning? Start the whole eroding-from-the-neck/accreting-at-the-poles again with each section?
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Re: 67P, why erosion from the neck?

Unread postby CharlesChandler » Fri Dec 19, 2014 8:13 am

viscount aero wrote:So you mean the + ions in the comet's atmosphere (coma) repel the + [heavier] ions in the bow shock, hence the standing off of the bow shock, detached.

The atmosphere around the comet starts out being neutrally charged. But as the comet moves through the IPM, neutrally charged atoms impinge on the neutrally charged boundary layer around the comet. When they do, the lighter electrons get stripped off, and the atomic nuclei burrow on into the boundary layer. This is when/how the boundary layer becomes positively charged. Then the charge increases with increased velocity.

viscount aero wrote:What do you mean by "core"? What if a comet has no core? What if the comet is just a piece of shattered debris?

Yes, I should have just said "the interior of the comet". I don't expect that there would be a chemically-differentiated core.

viscount aero wrote:They so badly want comets to be multi-billion-year old ancient building blocks that magically "seed the oceans of the Earth and icy moons".

Right -- it just goes to show you how tenaciously they'll cling to stuff that actually doesn't make all that much difference, just because they don't want to change their story. :roll:

viscount aero wrote:This is interesting as it describes the matter in the comas and tails simply "falling back down" onto the comet, albeit onto a modified surface (the developing peanut shape over time). This nullifies any notion of a comet being eroded or corroded away. The streaming mass/particles just reconfigure themselves back onto the etched comet body in a recycling process.

"Nullify" might be a strong word there. Also, even if everything is totally recycled, it doesn't mean that there isn't any corrosion going on -- that would just mean that the corrosion and the sedimentation would balance out. So you would have chemical etching and dust settling, aside from some of the stuff getting lost to the coma.

viscount aero wrote:I don't quite follow this when you say: "But if the impinging winds never actually get close to the surface, dust can accumulate."

I'm saying that anything that gets knocked loose from the surface, such as in the jets, might just settle back down, forming dust on the surface. This definitely wouldn't happen if the supersonic winds could come into direct contact with the surface.

I'll try to respond to your next post this evening.
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Re: 67P, why erosion from the neck?

Unread postby viscount aero » Fri Dec 19, 2014 11:55 am

CharlesChandler wrote:
viscount aero wrote:So you mean the + ions in the comet's atmosphere (coma) repel the + [heavier] ions in the bow shock, hence the standing off of the bow shock, detached.

The atmosphere around the comet starts out being neutrally charged. But as the comet moves through the IPM, neutrally charged atoms impinge on the neutrally charged boundary layer around the comet. When they do, the lighter electrons get stripped off, and the atomic nuclei burrow on into the boundary layer. This is when/how the boundary layer becomes positively charged. Then the charge increases with increased velocity.

viscount aero wrote:What do you mean by "core"? What if a comet has no core? What if the comet is just a piece of shattered debris?

Yes, I should have just said "the interior of the comet". I don't expect that there would be a chemically-differentiated core.

viscount aero wrote:They so badly want comets to be multi-billion-year old ancient building blocks that magically "seed the oceans of the Earth and icy moons".

Right -- it just goes to show you how tenaciously they'll cling to stuff that actually doesn't make all that much difference, just because they don't want to change their story. :roll:

viscount aero wrote:This is interesting as it describes the matter in the comas and tails simply "falling back down" onto the comet, albeit onto a modified surface (the developing peanut shape over time). This nullifies any notion of a comet being eroded or corroded away. The streaming mass/particles just reconfigure themselves back onto the etched comet body in a recycling process.

"Nullify" might be a strong word there. Also, even if everything is totally recycled, it doesn't mean that there isn't any corrosion going on -- that would just mean that the corrosion and the sedimentation would balance out. So you would have chemical etching and dust settling, aside from some of the stuff getting lost to the coma.

viscount aero wrote:I don't quite follow this when you say: "But if the impinging winds never actually get close to the surface, dust can accumulate."

I'm saying that anything that gets knocked loose from the surface, such as in the jets, might just settle back down, forming dust on the surface. This definitely wouldn't happen if the supersonic winds could come into direct contact with the surface.

I'll try to respond to your next post this evening.


Thanks for your clarifications, Charles.
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Re: 67P, why erosion from the neck?

Unread postby CharlesChandler » Fri Dec 19, 2014 6:14 pm

viscount aero wrote:The tails are not immune or necessarily isolated in a bubble. However this may not preclude the existence of a sheath :)

I'm not saying that it's just a bubble, as in a spherical halo surrounding the comet. It would be just a bubble if there wasn't any relative motion of the comet through the IPM, but then it's the relative motion that creates the boundary layer, and then separates charges in that boundary layer. So the sphere gets morphed into a teardrop, and ultimately, into an extremely long aspect-ratio teardrop (i.e., a cometary nucleus, with a halo around it, and a long coma trailing behind it).

BTW, I could clarify my description of the difference between the dust tail and the ion tail. The dust tail generally points away from the Sun, while it can have a bit of a curve to it, but the ion tail always points directly away from the Sun, and sometimes there is a split between the ion tail and the dust tail.

Image

IMO, both of these aspects of the coma are "mainly" just particles in the solar wind that were affected by the comet, with only "some" of the particles coming from the comet itself. (I have no idea what "mainly" and "some" mean here. ;) And again, this doesn't preclude corrosion on the surface of the comet.) Anyway, if there is a difference between the ion and dust tails, it is the difference between particles that are still charged, and thus are following the EM lines of force in the heliospheric current sheet (i.e., the so-called "flux tubes"), while the neutrally charged particles show no preference for the flux tubes, and simply trail behind the comet. And the curve comes from the lag in the time it takes for charges to recombine. In other words, a comet moving at roughly a constant velocity through the IPM should leave a linear trail, tracing the sum of the comet vector and the IPM vector. If neither of those change within the relevant time-frame, the vector addition is the same, and the trail is a straight line. If the trail curves, something changed. If it isn't the comet's vector, and if it isn't the solar wind's, something else is going on. So I think that the particles move directly away from the Sun while they are still charged, but once they get neutralized, they are free to trace the vector sum path, and their apparent path curves as the EM forces relax.

viscount aero wrote:I believe you posited this idea about the Chelyabinsk bolide, ie, Coulomb force.

Yes -- I'm using basically the same model for comets, asteroids, and meteoroids.

viscount aero wrote:There is no outer "crust", fixed jets, nor internal "geysers" happening on a comet in my opinion.

I see your point. So the "jets" can only be some sort of discharge between the surface and the cometary atmosphere. Maybe photo-ionization liberates electrons that are attracted to the positively-charged inner halo?

viscount aero wrote:I must finish my first draft and let you read it :)

Cool. I should keep my mouth shut while you develop your ideas, lest we try to develop a consensus before you've had a chance to see where your line of reasoning leads, which would be a mistake. ;)
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The ESA has access to expert astronomers

Unread postby MattEU » Sun Jan 04, 2015 6:36 pm

John Bowler, one of ours?

Asteroid theory crashes and burns

John Bowler (Letters, 31 December) is puzzled why the European Space Agency keeps saying that 67P is a comet. He claims it is an asteroid and objects to the ESA’s poor science.

A few clues. The ESA has access to expert astronomers, and might just know what it’s talking about. The name 67P/Churyumov–Gerasimenko is typical of comets; asteroid names have a different format. The P means “periodic comet”. It is listed as 67P/1969 R1 in the Planetary Data System Small Bodies Node table of comets. Asteroids
are mostly rocky or metallic, comets are thought to be mainly ice. The Philae lander confirmed that 67P is icy: it looks like a rock because it is covered in dust. Most asteroid orbits are approximately circular; 67P ranges between 1.24 and 5.68 AU from the sun. When comets approach the sun, the ice turns to vapour, creating a haze (or coma”) that sometimes develops into the characteristic tail. The main purpose of the Rosetta mission is to follow 67P as it undergoes this process. When discovered in 1969, 67P had a coma and a tail one arc-minute long. Its 1996 appearance showed a slightly larger coma. Although the best-known comets have highly eccentric long-period orbits, there are also many short-period comets that stay closer to the sun, and 67P is one of these.

Mr Bowler apparently can’t tell his comet from his asteroid.
Professor Ian Stewart
University of Warwick


Tough dust and it seems that I must have missed the fact that comet 67p was confirmed to be icy ...

Are those the same ESA experts who predicted that comet 67p was a dirty snowball and nice and round in shape etc? No jets coming from the neck of the peanut shape or massive cliffs and boulders on its surface ...
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Re: The ESA has access to expert astronomers

Unread postby viscount aero » Sun Jan 04, 2015 8:16 pm

MattEU wrote:John Bowler, one of ours?

Asteroid theory crashes and burns

John Bowler (Letters, 31 December) is puzzled why the European Space Agency keeps saying that 67P is a comet. He claims it is an asteroid and objects to the ESA’s poor science.

A few clues. The ESA has access to expert astronomers, and might just know what it’s talking about. The name 67P/Churyumov–Gerasimenko is typical of comets; asteroid names have a different format. The P means “periodic comet”. It is listed as 67P/1969 R1 in the Planetary Data System Small Bodies Node table of comets. Asteroids
are mostly rocky or metallic, comets are thought to be mainly ice. The Philae lander confirmed that 67P is icy: it looks like a rock because it is covered in dust. Most asteroid orbits are approximately circular; 67P ranges between 1.24 and 5.68 AU from the sun. When comets approach the sun, the ice turns to vapour, creating a haze (or coma”) that sometimes develops into the characteristic tail. The main purpose of the Rosetta mission is to follow 67P as it undergoes this process. When discovered in 1969, 67P had a coma and a tail one arc-minute long. Its 1996 appearance showed a slightly larger coma. Although the best-known comets have highly eccentric long-period orbits, there are also many short-period comets that stay closer to the sun, and 67P is one of these.

Mr Bowler apparently can’t tell his comet from his asteroid.
Professor Ian Stewart
University of Warwick


Tough dust and it seems that I must have missed the fact that comet 67p was confirmed to be icy ...

Are those the same ESA experts who predicted that comet 67p was a dirty snowball and nice and round in shape etc? No jets coming from the neck of the peanut shape or massive cliffs and boulders on its surface ...


That's pretty funny on many levels.

There are now mainstream cracks appearing. And notice the arrogance and condescending tone of the "expert" who lambastes John Bowler. As they say "pride before a fall..."
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Re: 67P, why erosion from the neck?

Unread postby Frantic » Mon Apr 27, 2015 12:50 pm

Interesting article that seems to be related to our discussion of erosion on 67P.

http://www.space.com/29182-mars-rover-curiosity-wheel-damage-corrosion.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29

Frantic wrote:http://en.wikipedia.org/wiki/Debye%E2%8 ... kel_theory

Debye–Hückel theory is an adjustment to account for the reality of electrolytic solutions with their ionic nature. Activity coefficients effectively represent concentrations. Where the comet is concave (the neck) it has the most surface exposed to itself. If there are surface corrosion reactions, we will have much higher ionic activity in this concave area, which equates to higher activity (or concentration), and therefore more reactions. The electrolytic environment has bounds limited by the ability of a charged entity to attract another. I don't know where the bounds would be, but the convex area would be most likely to fall within those bounds. There would be a larger build up of gases and ions in this area around the neck than else where. A charge differential between the nucleus and coma creates jets?

As there would be far more activity at the neck, there should be, I think, less activity on the rounded lobes.

Notice the directions of the jets in the ESA images that are over exposed. Hard to tell, but none of the jets are perpendicular to the neck, and there are clearly multiples jets. I don't think the center of the neck is eroding, but rather the cliff faces on each side of the neck.



CharlesChandler wrote:If the surface was positively charged, I'd say that it was just the positive charge that was liberating atoms by removing the covalent bonding. So whichever chemicals had the lowest ionization potentials would be the first to go, leaving stronger bonds in place, producing selective corrosion, and possible pitting of the surface. If the surface is negatively charged, it wouldn't seem to have this problem. But then again, when exposed to the unfiltered light from the Sun, photo-ionization might make the day side of the comet positively charged, with the night side picking up an equal-but-opposite negative charge.


Viscount Aero wrote:there is no "interior jetting" happening. The jetting is all happening on the outside of the comet, from its surface. It must be this way because:

• The comet is a rotating body on an axis, yet the tail remains pointed in one direction--not following the axial rotation of the comet. In other words, the tail is independent of the axial rotation of the comet. This is evidence that the jetting is not coming from the interior of the comet but originates on the outside of the comet
• No physical vents, structures, holes, caves, cracks, are ever seen on a comet's surface where the jetting is coming from.
• Locations of the jetting change perpetually (to my knowledge).
• For the solar wind to affect the tails, causing the tails to LEAD the comet on its outbound trajectory, the "jetting" must be coming from the surface.
• Were jetting coming from the interior of the comet, the jetting would be coming from fixed locations, spiraling the ejecta around the comet as it rotates about an axis. But this is not observed.


Viscount Aero wrote:
CharlesChandler wrote:But that would be a truly enormous amount of erosion going on, and it's a bit hard to believe that there would be much left of the comet after just one trip through the inner solar system. Then it becomes impossible to explain regularly recurring events such as Halley's Comet, whose orbital period should change dramatically with the mass loss, since lighter objects have lower terminal velocities, encountering more friction per mass than large objects.



Yes and this is why they invented the Oort Cloud. The Oort Cloud is a bandaid to get around this problem (mostly). They so badly want comets to be multi-billion-year old ancient building blocks that magically "seed the oceans of the Earth and icy moons". But per the "erosion" problem, they can't visit the Sun very often before they are totally eaten away or break apart. So they invented the "Oort Cloud" as a vast "holding pen" where some mysterious dark forces dislodge the occasional comet--sent on to the Sun--to resupply the comet stream and explain away the erosion problem. Halley's Comet was only "recently perturbed" from the "Oort Cloud" and sent to the Sun. Halley's Comet is alleged to be "4 billon years old" but has only "recently" visited the Sun.
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Re: 67P, why erosion from the neck?

Unread postby seasmith » Mon May 18, 2015 5:00 pm

"
OSIRIS discovers balancing rock on Comet 67P"
Scientists from Rosetta’s OSIRIS team have discovered an extraordinary formation on the larger lobe of comet 67P/Churyumov-Gerasimenko in the Aker region. From a group of three boulders, the largest one with a diameter of approximately 98 feet (30 meters) stands out: images obtained September 16, 2014, from a distance of 18 miles (29 kilometers) with the help of Rosetta’s scientific imaging system OSIRIS show it to perch on the rim of a small depression. There seems to be only a small contact area with the nucleus.


charge inflows and outflows ?

Image

http://www.astronomy.com/news/2015/05/o ... -comet-67p
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