What did "we (i.e. mainstream physics)" get right before the space craft missions to comets? Seemed to be FULL of surprises each time a new comet nucleus was encountered!
Oh what a surprise! We have telescope views of comets and interprete them, in different wavelength etc. We come up with a model of how it works and in the early 50s Fred Whipple comes up with the term dirty snowball. A few years later Alfven comes up with the theory how tails are created. All WITHOUT in-situ measurements. This was picked up in popular literature, the dirty snowball. After first views of an actual cometary nucleus (Giotto @ Halley) we get another view, that maybe it is more like a "snowy dirtball", but that was not changed in popular literature. However, the draping of the field creating the tail is confirmed. But naturally there are going to be surprises. If everything was know than we could close all research institutes (which would save a lot of taxpayers money).
Are you a believer in the
Dirty Snowball Model of comets tusenfem? ie ..
• Comets are composed of undifferentiated “protoplanetary debris” - dust and ices left over from the formation of the solar system billions of years ago.
• Radiant heat from the Sun sublimates the ices. The vapor expands around the nucleus to form the coma and is swept back by the solar wind to form the tail.
• Over repeated passages around the Sun, solar heat vaporizes surface ice and leaves a “rind” of dust.
• Where heat penetrates the surface of a blackened, shallow crust, pockets of gas form. Where the pressure breaks through the surface, energetic jets form.
No, I do not believe in the dirty snowball, because with the missions we had we know that that was not the correct description, and the model
develops itself, as we gather more data. We have seen the surfaces of comets in more detail, we have seen there a lot of dust on the surface, we have also seen that the albedo is one of the lowest that you can find in the solar system (i.e. the blackestest surfaces in the solar system). We have seen that dust collects itself in dells on the surface of the comet from pictures (we don't want Philae to land in such a region, because of the low gravity it might not be compacted and can be anyone's guess how deep).
Getting better views of comets, getting the size/volume, knowing the mass, we know that it has to be porous material.
If you have long-period comets, then yes, they are probably "pristine" ould matter, however 67P/CG with a 6 year orbit, has passed by the sun often and the surface will definitely be "weathered" (in my opinion) with little volatiles on the surface. The craters in the surface of the comets show that there are impacts of smaller bodies (micro-meteorites) on the nuclei, also creating dust.
Vapour/gas escapes from the comet, and dust too. Part of the gas gets ionized and picked up by the solar wind magnetic field. The plasma will impede the magnetic field to flow aroundthe nucleus and gets hung up (Alfven's model). That is the gas/ion tail. The dust that escapes from the surface basically follows behind the comet and gets blown outward by the solar wind and radiation.
As soon as the comet enters Jupiter's orbit the solar irradiation is strong enough to start warming up the nucleus. Outgassing starts, which can be variable which we know, and which 67P/CG has also shown.
Has any of the above changed since the actual encounters of spacecraft with comets?
Yes, things are in a constant flux of further understanding.
That is what science is, studying stuff, and improving the models that you have with the new data. That is why we send Rosetta in space, not "to confirm the 1950's dirty snowball" but to get the best data ever to understand comets.
Electrostatic charging of the comet nucleus,[3] and, charging of the dust,[4] resulting in levitation of dust from the comet surface,[4]
Yes, the nucleus will be charged, probably not as much as a large asteroid (as in the paper linked above), dust naturally can also be charged (just do a literature search on dusty plasmas at comets). Levitation? maybe, apparently it does not happen as much on the moon as thought. With the escape velocity much much smaller at the comet, the dust if it levitates, will probably be lost to the comet in the dust tail (the charged dust does not magnetize that well).
Coagulation of grains with opposite potentials,[5] and the opposite process, disruption (break-up) of grains with high potentials,[4]
That will be less likely near the comet, as far as I know (I am not a dust expert) the sticking together of dust does not happen that much. Just oppositely charged is not enough, collisions will most often lead to charge exchange and not clinging together.
Plasma instabilities in the tail,[4]
Duh! there are dozens of papers on plasma instabilities in the tail in mainstream science.
Folding of the interplanetary magnetic field into the tail of the comet (Alfvén's "folding umbrella" hydromagnetic model, 1957)[6] [7]
Already said above, the draping of the field around the comet, creating the tail. All mainstream, nothing EC there. Does the EC say anything about nested fields? Did you know that if you fly by Halley, you can actually see the various direction changes that happened in the solar wind in the piled up magnetic field in the cometosheath?
A cometary current system including plasma tail streamers separated by a neutral current sheet, with a total current exceeding 108A,[7]
A shock-ionopause current system, a tail current system, and a field-aligned auroral current system,[2]
Well, total current could well be 108 A and if Mendis says so about the streamers, then it will probably be so (I would need to read that paper, but it is too late now). Naturally, there is a current sheet in the tail, because of the oppositely directed magnetic field and there will be other current sheets, e.g. at the front in the magnetosheath (see Laakso 1997).
Don't know what a "shock-ionopause" is, so I cannot comment on that.
Naturally, with the tail being dynamic, just as at Earth, there can be reconnection and tail detachment events, and that can lead to acceleration of particles towards the comet. If that can actually lead to "aurora" as Mendis seems to claim, I am skeptical.
The flow of such field-aligned currents leading to the generation of strong localized field-aligned electric fields (double layers),[2] [8]
The creation of double layers depends on a lot of stuff. electric field will be there, and have been observed (see Laakso), but not every electric field is a double layer, the EU/ES/EC crowd does not seem to understand that.
Acceleration of electrons to keV energies in such double layers would lead to the observed enhanced fluxes of suprathermal electrons.[2]
There are LOTS of methods to get suprathermal electrons, double layers are not the magical objects that the EU/ES/EC want them to be, and as above, not every electric field is a double layer.
Production of X-rays (e.g. such as those detected from Comet Hyakutake,[9][10][11] confirming the presence of Birkeland currents (field-align currents),[12]
NO no no, that has already been discussed above. The X-rays are completely described by charge exchange events between highly ionized solar wind ions (e.g. O7+) with neutrals from the comet. This is for the line production (and shown to by laboratory experiments!!), the background production is completely described by bremsstrahlung of electrons in the cloud (see page 8 if I am not mistaken, discussion by Tim Thompson). I see no reason whatsoever that Xrays are confirming the presence of "birkeland currents" (but I think Ian Tresman should write there field aligned currents).
Jets, such as those produced and modelled by Kristian Birkeland's theory,[13]
Birkeland's theory does not explain jets. All the ideas of Birkeland have no merit, because of false assumptions.
The generation of magnetic fields and electric currents in cometary plasma tails, up to a billion Amps, [14] first proposed by Alfvén in 1957,[6] and "strikingly established during the crossing of the plasma tail of Comet Giacobini—Zinner by the ICE spacecraft on September 11, 1985 (Smith et al., 1986)"[15] [7]
The magnetic field in the tail is solar wind magnetic field not created by plasma currents, but the other way around, plasma currents (the cross tail current) is created by the magnetic field. And yes, it was measured by ICE.
Currents in the cometary atmosphere,[16]
Same point over and over again.
Outbursts from the comet nucleus resulting form macroscopic electric double layers,[17]
No idea, I see an abstract of a conference presentation there, and it reads rather weird.
The origin of comet striae (banding) in dust tails,[18]
Sorry, no dust expert here.
Inner coma cometary plasma formation by the critical ionization velocity mechanism,[19] [20]
CIV could play a role near comets, but only when we get there can we get actual insight in whether it is really important.
Filamentary structure in comet tails interpreted as evidence of field-aligned currents (Birkeland currents),[7]
Again currents?
A "cometary aurora" due to "current discharges into the atmosphere from the tail"[21]
Substorm process on the comet tail see above (methinks Ian Tresman repeats himself a bit much)
Possible ionization of the inner coma due to cross-tail currents closing through the cometary head.[22]
Looking at what Mendis writes, it is not clear whether this actually happens or is possible near the comet.
Where you surprised by jets on the "dark" side of comet nucleus tusenfem? Or did you or the mainstream expect it?
In 2004, NASA's Stardust spacecraft on a mission to comet Wild 2 (pronounced "Vilt 2"), "found 20 jets, on both the sunlit side of the comet and, surprisingly, the dark side".[23][24]
I was not working on cometary physics back then, but I see no reason why it could not happen. The comet rotates gets heated and it can well be that the pressure unloads itself on the back side too, but the day side would be more logical. I cannot get to the Science paper which models this, though.
So, now Ian Tresman only cited mainstream physics, so you can hardly say that that is the EC view.
Now why don't you cite us some EC papers?
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