Scientists help solve mystery of why comets emit X-rays

March 13, 2018, Rutherford Appleton Laboratory
Credit: CC0 Public Domain

The mystery of why comets travelling through Space give off X-ray emissions has been solved thanks to new research undertaken by a team that included science staff from STFC's Central Laser Facility (CLF) and RAL Space.

Scientists have long wondered why comets can radiate X-rays, given that X-rays are normally associated with hot objects like the Sun but comets are among the coldest objects in the Solar system.

When comets travel through the Solar system they interact with the Solar radiation, the Solar wind and the Solar magnetic field. This interaction produces a visible atmosphere or coma around the comet and the observed cometary tail, and in some cases produces X-rays. These X-rays are generated on the Sunward side of the comet where the Solar wind impacts the cometary atmosphere forming a bow shock.

To investigate how X-rays can be emitted from a comet, a team of scientists from 15 research institutes performed experiments at the LULI laser facility in Paris where they replicated the interaction of the Solar-wind with a comet.

The STFC team involved in the project were instrumental in coming up with the scientific model for the interaction of the with the comet. This included the theoretical model for the generation of plasma turbulence, the acceleration of electrons by the turbulence and the X-ray emission from the accelerated electrons. The STFC team also supported a team from the University of Oxford in numerical simulations and undertook the target fabrication.

CLF's Professor Bob Bingham led the STFC team involved in the project and said

"These experimental results are important as they provide direct laboratory evidence that objects moving through magnetized plasmas can be sites of electron acceleration- a very general situation in astrophysics that takes place not only in comets, but also in planetary magnetospheres, such as our own Earth, or even in supernova remnants, where the ejected material moves across the interstellar gas. The experiments also confirm theoretical models developed by the team."

Other members of the STFC team included CLF's Dr. Raoul Trines and Chris Spindloe and from STFC's RAL Space facility Dr. Ruth Bamford.

Electron acceleration in laboratory bow shock. Credit: F. Cruz and L. O. Silva, IST Lisbon, Portugal

For CLF's Dr. Raoul Trines the highlight of the project was reproducing a force of Nature

"As a theorist I find it amazing that it is possible to sensibly replicate astrophysical phenomena in the laboratory, to test our physical understanding of what Nature gets up to".

For the experiments the research team fired laser beams onto a plastic foil, which exploded, causing a stream of electrons and ions to be expelled, forming a high speed flow of ionized gas (plasma) like the Solar wind. This 'plasma flow' then impacted onto a solid sphere, the so-called laboratory `comet', placed nearly a centimetre away from the plastic foil, resembles what happens when a real passes through the Solar system. It was found that electrons are heated to about a million degrees in the up-stream plasma by plasma turbulence.

These hot electrons are responsible for emitting X-rays but only in the presence of a magnetic field.

This work also sheds light on a cosmic ray mystery known as the injection problem. It is widely recognised that strong shock waves are expected to accelerate particles to very high energies, however, they require a source of particles fast enough to cross the shock, the injection problem. Each time the particles cross the shock they gain energy. This latest experiment clearly demonstrates that can provide a source of fast particles overcoming the injection problem.

From the space science point of view, this research has been important in better understanding the mechanisms that create cosmic rays. The most hazardous cosmic rays are the energetic particles either from the Sun or outside the Solar system. They can penetrate even thick walls like tiny bullets and present a very serious hazard to both astronauts and spacecraft technology. Billions of pounds can be at risk due to Space Weather (as it is known) damaging satellites. Astronauts on long term missions outside the Earth's magnetosphere could receive life threatening doses of radiation from such particles. In order to protect them we need to understand how this radiation is created so we can predict it and give warnings or even shield against it using similar mechanisms to that which created it.

A laboratory experiment like this enables us to test our understanding of how are accelerated to such high energies, in a controlled environment. Something that is not easy to do directly in space.

The paper has been published in Nature Physics.

Explore further: Cosmic bow shocks

More information: A. Rigby et al. Electron acceleration by wave turbulence in a magnetized plasma, Nature Physics (2018). DOI: 10.1038/s41567-018-0059-2

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RealityCheck
1.6 / 5 (7) Mar 13, 2018
@jonesdave and cantdrive85.

Before you two 'get nasty' with each other again....please don't! :)

Anyhow, the X-ray observations mean that 'fast-electron currents' phenomenon arises in all 'plasma flow' situations, as above experimenters confirm (and as I also again recently 'reminded' all).

Moreover, this lab experiment also confirms that the X-rays are emitted ONLY in the presence of MAGNETIC fields; so there is the experimental confirmation of the SYNCHROTRON RADIATION which I and others have always maintained is generated all over the universe by ordinary (and NOT 'exotic' DM etc etc fantasy) processes.

So @jonesdave------and all who've been attacking @cantrive85 et al with the claim that "No synchrotron radiation detected, hence no electric currents etc etc"------will you now cease your 'demands' for proof of SYNCHROTRON; since above experimenters confirmed it does happen due to electric currents arising in all 'plasma flow' situations (as I have said all along).? :)
Da Schneib
5 / 5 (4) Mar 13, 2018
Moreover, this lab experiment also confirms that the X-rays are emitted ONLY in the presence of MAGNETIC fields
Ummmwut?

X-rays are produced for use in imaging by shooting high-energy electrons at a metal target. No magnets involved.

On Earth.
Uncle Ira
5 / 5 (5) Mar 13, 2018
@ Really-Skippy. How you are Cher? I am good me, thanks for asking.

@jonesdave and cantdrive85.


And,

@jonesdave


Cher, I think you are on the wrong article. They did not chime in on this one yet. You need to look in on the other articles where they are arguing unless you just wanted that they argue on this one too.
RealityCheck
1 / 5 (3) Mar 13, 2018
@Da Schneib.
Moreover, this lab experiment also confirms that the X-rays are emitted ONLY in the presence of MAGNETIC fields
Ummmwut? X-rays are produced for use in imaging by shooting high-energy electrons at a metal target. No magnets involved.
Please read/comprehend in the specific context...
For the experiments the research team fired laser beams onto a plastic foil, which exploded, causing a stream of electrons and ions to be expelled, forming a high speed flow of ionized gas (plasma) LIKE SOLAR WIND. This 'PLASMA FLOW' then impacted onto a solid sphere, the so-called laboratory `COMET', placed nearly a centimetre away from the plastic foil, resembles what happens when a real comet passes through the Solar system. It was found that electrons are heated to about a million degrees in the up-stream plasma by plasma turbulence. These HOT electrons are responsible for EMITTING X-RAYS but only in the presence of a MAGNETIC FIELD.
Thanks. :)
RealityCheck
1 / 5 (3) Mar 13, 2018
@mackita.
These hot electrons are responsible for emitting X-rays but only in the presence of a magnetic field
High voltage lightning can be observed in dusty volcanos, the https://www.techn...ch-tape/ can also generate X-rays in vacuum just by friction = magnetic field shouldn't be necessary.
Please also see my response to @Da Schneib above. The Magnetic Field aspect/comments related ONLY to above 'plasma flow' situation onto/around COMETS; and the experimenters confirmed there must be HOT (aka FAST) electron currents at comet which MUST BE affected by some Magnetic Field; as per their in-context statement:
These HOT electrons are responsible for EMITTING X-RAYS but only in the presence of a MAGNETIC FIELD.
Thanks. :)
RealityCheck
2 / 5 (4) Mar 13, 2018
@Uncle Ira.
@ Really-Skippy. How you are Cher? I am good me, thanks for asking.

@jonesdave and cantdrive85.


And,

@jonesdave


Cher, I think you are on the wrong article. They did not chime in on this one yet. You need to look in on the other articles where they are arguing unless you just wanted that they argue on this one too.
Consider the subject matter: COMETS. And ELECTRIC CURRENTS; And MAGNETIC FIELDS.

The very things @jonesdave and @cantdrive85 have been arguing about every thread these subject matter come up. How long did you think it would be, before those two 'got stuck into' this thread topic (and each other!), Ira?

I merely got in before they noticed this thread and started to 'get nasty' with each other again; with a plea NOT to do that. While pointing out things which they could discuss politely this time (what are the chances of that happening this time, Ira?). :)

Uncle Ira
4 / 5 (4) Mar 13, 2018
what are the chances of that happening this time, Ira?
Well knowing the can't-Skippy like I do know him, I would say your chances are about zero, maybe less.
Da Schneib
5 / 5 (1) Mar 14, 2018
@RC, actually it's not synchrotron radiation, it's bremsstrahlung. Synchrotron radiation is polarized; bremsstrahlung is not. And that's only one of its signatures.
RealityCheck
1 / 5 (3) Mar 14, 2018
@Da Schneib.
@RC, actually it's not synchrotron radiation, it's bremsstrahlung. Synchrotron radiation is polarized; bremsstrahlung is not. And that's only one of its signatures.
Again, please pay particular attention to the situation/context. For example, it's NOT 'braked' electrons, it's 'accelerated' (to fast/hot motional state) electrons; hence NO 'Bremsstrahlung' (braking radiation) as such; moreover, it's NOT motion through 'neutral' (eg, atomic/molecular gaseous) media; but rather, through conductive PLASMA; so the 'study target' phenomena/radiation involved in this situation is therefore Synchrotron Radiation from fast-electrons moving in 'accelerating/spiraling manner' along Magnetic Fields, which the team also specifically state must BE there in such 'plasma flow' situation at/around comet moving/interacting with Solar Wind and 'local plasma flows' at comet itself (which give rise to 'shock heated/accelerated fast-electron currents as described by team). :)
RealityCheck
1 / 5 (3) Mar 14, 2018
@mackita.
See for example https://www.scien...5500932. The particle collisions and friction generate high voltage, once it gets higher than some 10 - 40 kV, then the X-rays can be formed in vacuum. In air the electrons are slow down by air molecules.
Yes, as the lab study of this article says: the plasma flows within/across shock layers heats up and accelerates the fast electrons; which then move through that CONDUCTIVE plasma, NOT through air or other 'neutral' media. So in that situation studied/experimented, the ONLY radiation by fast moving electrons through conductive plasma is most likely synchrotron type radiation as the fast electrons move in 'spiraling paths' within magnetic fields at whatever 'spiral circuit' frequency' applies.

So, again @mackita, please also see my above response to @Da Schneib's own misunderstanding of the actual context/phenomena being specifically treated in the above-described experiment. :)
Da Schneib
5 / 5 (3) Mar 14, 2018
@RC, synchrotron radiation comes from synchrotrons. That's why it's called "synchrotron radiation." It's readily detected by polarization and other signatures.

Bremsstrahlung is not "braking radiation;" it's radiation due to the acceleration of electrons. It doesn't matter whether there's plasma involved or not. If you had actually read the paper you'd have read that the primary cause of the X-ray emissions in the experiment was due to bremsstrahlung. Says so right there. Go ahead and text search the paper. Notably, synchrotron radiation is not mentioned.
cantdrive85
1 / 5 (2) Mar 14, 2018
what are the chances of that happening this time, Ira?

Well knowing the can't-Skippy like I do know him, I would say your chances are about zero, maybe less.

Definitely less, I can't resist tearing down the dirty snowball nonsense. Besides, it's the low hanging pseudoscience easily picked and cast aside.
And in plasmas, those "shocks" behave like double layers and it is the electric fields in those DL's accelerating the electrons.
Da Schneib
4.2 / 5 (5) Mar 14, 2018
Whatever @macurinetherapy is babbling about it has nothing to do with this article; typical energies here are on the close order of 700 eV, not 10-40 keV (10,000-40,000 eV).

Meanwhile, @cantthink69, why is it that a magnetic field is required?

Just askin'.
RealityCheck
1 / 5 (3) Mar 14, 2018
@Da Schneib.
@RC, synchrotron radiation comes from synchrotrons. That's why it's called "synchrotron radiation.
Yes, that's why any 'spiraling circuit' electron along magnetic field 'lines' is characterized as "Synchrotron" (a specific type of "cyclotron") because of the cycling loop paths followed by charges in whatever 'variable loop diameter' spiraling applies.

And here is the mention of cyclotron (synchrotron) frequency in the paper:
Supplementary Table S1 shows that while many of the parameters such as CYCLOTRON frequencies and gyro radii are very different between the laboratory and astrophysical cases, scaled quantities, such as the ratio of gyro radii to skin depth, are conversely fairly similar.


And since the fast electrons move along magnetic field 'lines' (as the paper also states), then X-ray radiation must also involve 'synchrotron/cyclotron' type.

FYI, mate, German "Bremstrahlung" translates to Braking Radiation (negative acceleration). :)
Da Schneib
5 / 5 (2) Mar 14, 2018
But cyclotron and synchrotron radiation are different, @RC.

And you didn't look at Figure 1 in the paper, which shows the electrons' paths being bent by an external magnetic field (the solar wind magnetic field), not a field from the comet as in the lab experiment. So the direction of the X-rays is different.

I'm aware of what bremsstrahlung means; it's used for radiation created by any type of acceleration of charged particles, not just braking of electrons.

Meanwhile, polarization, which is a characteristic of both cyclotron and synchrotron radiation, is not mentioned in the paper.

There is no synchrotron or cyclotron radiation here. It's just ordinary bremsstrahlung. It's from the bend in the electrons' path when they get into the magnetic field of the solar wind.
Da Schneib
5 / 5 (1) Mar 14, 2018
Oh and BTW the cyclotron frequencies refer to the acceleration of the electrons by the solar and cometary plasmas, not to the generation of the bremsstrahlung. There are two parts:

1. Acceleration of the cometary plasma's charged particles
2. Generation of bremsstrahlung when the accelerated electrons meet the solar wind magnetic field

You'll want to keep that in mind. Apparently you're not differentiating between them.
Da Schneib
3 / 5 (2) Mar 14, 2018
And lastly, I think this is a very hypothetical paper. I question strongly whether the lab results actually duplicate anything happening around comets. I'd like to see some commentary by our astrophysics experts, and I'll also wait to see what comments come out on this paper later when the general astrophysics community has a while to comment. The limitations of the FLASH code are well documented, just to note one factor that could compromise the analysis.

To make the lab look more like a real comet, I'd like to see an external magnetic field used rather than magnetizing the obstacle in the experiment.
milnik
1 / 5 (1) Mar 18, 2018
X-rays are produced in scientific institutions, and scientists do not know how comets can emit these rays. If the accelerated electron slows down to the core of the atom, it emits X-ray rays.
If the comet goes at a higher speed through a magnetic field, and if it contains a plasma, it is certain that it will emit not only the X-ray, but also several other electromagnetic waves, because the comet is part of a decayed body that is broken due to strong magnetism.
RealityCheck
1 / 5 (3) Mar 19, 2018
@Da Schneib.

Firstly: thanks for your polite responses; much appreciated. :)
Oh and BTW the cyclotron frequencies refer to the acceleration of the electrons by the solar and cometary plasmas,
Yes; and also by magnetic fields arising with/around those plasma flows and around comet stretching from 'stagnation zone' at leading edge, to 'tailing zone' at/behind trailing edge). MY pint was that all these accelerated 'fast' electron 'currents' are swirling around along/across magnetic fields, and so inevitably emit a mixed spectrum of X-rays. And...
bremsstrahlung
Bremsstrahlung 'label' should ONLY apply to slowing SPEED cases, as originally intended. Its 'generic' use, for cases where NO speed reduction is involved, is misleading. The 'fast' electrons in this case are merely changing direction; ie, non-slowing 'velocity' changes (illustrative analogy: gravitational 'orbital' velocity changes do not necessarily involve 'speed' reduction of satellites).

cont...
RealityCheck
1 / 5 (4) Mar 19, 2018
cont.. @Da Schneib.
To make the lab look more like a real comet, I'd like to see an external magnetic field used rather than magnetizing the obstacle in the experiment.
Yes, I saw that too. Perhaps they wanted to 'cover all bases', so to speak. Which was prudent in my opinion; since there is 'quite a lot happening' in such 'comets-in-solar-wind' situations; eg:

- material may be 'magnetic' t start with (magnetite ore);

- outgassing causes 'static buildup' and discharges along/across the plumes and cometary body and surrounding plasma 'structure/flows (further creating induced-magnetizing/polarizing etc phenomena;

- heating/outgassing pressures may distort/squeeze silica/other compounds t produce 'piezo-electric' currents/discharges etc;

- plasma flows, fast electron currents, may 'feedback' and intensify all such 'seed voltage/currents' phenomena; to create an 'overall cometary system wide' electro-magnetic-plasmic circuitry/charge 'structure'?

Thanks again, DS. :)
Da Schneib
5 / 5 (2) Mar 19, 2018
But @RC, you were claiming the X-rays were synchrotron radiation in the first post on this thread. They're not.
RealityCheck
1 / 5 (3) Mar 19, 2018
@Da Schneib.
But @RC, you were claiming the X-rays were synchrotron radiation in the first post on this thread. They're not.
I merely point out the known/obvious situation: that the fast electrons do NOT 'stop moving'; they are merely 'redirected' UN-slowed along changed trajectories spiraling around within different mag-fields, that's all. So, unless they are being 'slowed/stopped' (in which case they WOULD emit Bremsstrahlung type X-rays), then they will only be changing direction in their looping paths; and hence MUST emit 'cyclotron/synchrotron' type X-rays.

That's why called 'synchrotron radiation' in the first place ('changing loop pathways' NOT 'slowing/stopping'). Which is why (as I said above, did you see it?) the term 'Bremsstrahlung' as a 'generic' label is misleading and should NO LONGER be used for all cases/types (as above group/you/wiki do).

So are they/you claiming the fast electrons are 'slowed/stopped', instead of just being 'redirected' UN-slowed?
RealityCheck
1 / 5 (3) Mar 19, 2018
PS @Da Schneib: mate, I am called away again and may not be back for another few days; so if I miss your next I will try and get back to you when I return. Until then, thanks again for your time, trouble and polite responses; again, much appreciated. Cheers and good health 'til then, DS, everyone! Bye for now. :)
jonesdave
3 / 5 (4) Mar 19, 2018

And in plasmas, those "shocks" behave like double layers and it is the electric fields in those DL's accelerating the electrons.


Wrong. The reason comets emit x-rays has been known for some years. It was a bit of a surprise when they first detected them in '96 at Hyakutake. In retrospect, it should have been predictable. I guess nobody thought to look, until then. The x-rays have specific signatures which shows that they come from charge exchange reactions between the solar wind heavy ions, and cometary neutrals. So, an O7+ will grab an electron from H2O, and you get O6+ and H2O+. As the excited O ion relaxes, it emits an x-ray. It is then possible to see which ion was involved from this line emission.
Not sure about the article above, but I thought Bremstrahlung has long been known about. Have to check.
Charge Exchange-Induced X-Ray Emission from Comet C/1999 S4 (LINEAR)
http://science.sc...520/1343
Lisse, C. M. et al.
jonesdave
3.7 / 5 (3) Mar 19, 2018
Definitely less, I can't resist tearing down the dirty snowball nonsense. Besides, it's the low hanging pseudoscience easily picked and cast aside.


Lol. We've just had a two year mission to a comet. The only pseudoscience that got shot down was the idiotic, mythology inspired electric comet woo. Not a single piece of evidence, over how many missions now? Sorry, Velikovsky was an idiot, and so are Thornhill and Talbott.

jonesdave
3 / 5 (4) Mar 19, 2018
Actually, the paper I linked upthread is paywalled. This one might be better:

Spectral analysis of the Chandra comet survey
Bodewits, D. et al
https://www.aanda...ght.html
Da Schneib
5 / 5 (1) Mar 19, 2018
Actually, both synchrotron and cyclotron radiation are types of bremsstrahlung, but they can be differentiated from other types by their polarization so while it's equally accurate to use either terminology it's more specific to call it synchrotron or cyclotron radiation if it shows the appropriate polarization characteristics. In this case, there is no polarization, so this radiation is merely bremsstrahlung, not either synchrotron or cyclotron radiation. As I am now pointing out for the third time on this thread.

Also, the difference between synchrotron and cyclotron radiation is determined by whether the charged particles that generate it are relativistic or not. So it is incorrect to refer to it as "synchrotron/cyclotron" radiation; we can see the difference between them without having to check the motion of the charged particles.

[contd]
Da Schneib
5 / 5 (1) Mar 19, 2018
[contd]
In addition to all this, if charged particles emit bremsstrahlung, then their speed (the scalar, not just the velocity i.e. the magnitude not just the direction) must be reduced in order to change their momentum. Otherwise the bremsstrahlung would be free energy from nowhere, violating energy conservation.

So are they/you claiming the fast electrons are 'slowed/stopped', instead of just being 'redirected' UN-slowed?
Errrr, I don't think you're getting how this works. The momentum of the charged particles has to change and in fact be reduced for there to be any type of bremsstrahlung, and this includes synchrotron and cyclotron radiation. It's not enough to merely change the direction of their velocity and in fact immaterial. The magnitude of the velocity must change.

You're completely wrong on this one and have been since your first post on this thread. It's unfortunate you don't have the courage to admit it.
jonesdave
2.3 / 5 (3) Mar 19, 2018
I'm not at all convinced by this paper, to be honest. This phenomenon at comets has been well studied now, and CX reactions fit the data very well, both in emission and the location of that emission. This paper seems tho have the emission at the bow shock, but the paper I linked from Bodewits et al see it well inside the bow shock. I'm also surprised that the authors have not referenced any papers from the data collected by craft traversing cometary bow shocks, as at Halley, for instance. Did these spacecraft see those waves? I'll have to check, but that would still put it in the wrong location, as reported by Bodewits et al.
jonesdave
2.8 / 5 (4) Mar 19, 2018
As regards bremsstrahlung; the authors say in fig. 5 from the paper that there is minimal contribution.

Electron acceleration by wave turbulence in a magnetized plasma
https://www.natur...8-0059-2
Rigby, A. et al.
Da Schneib
5 / 5 (1) Mar 19, 2018
@jones, it's very important to note that the source and orientation of the magnetic fields in the real situation and the lab simulation are different enough that there may be some confusion based on which situation the writers of the paper are talking about. This may account for some of the confusion about the bow shock origin of the X-rays.

It's also important to keep in mind that there may be more than one source for the X-rays.

There is only one other source for the X-rays and that's K-transitions after an electron is knocked out of the K-shell of an atom and electrons in higher shells replace it.

The reference in Fig. 5 doesn't say the bremsstrahlung contribution is *always* minimal; it says quite clearly it's minimal *if there are no hot electrons.*
jonesdave
3 / 5 (4) Mar 19, 2018
@jones, it's very important to note that the source and orientation of the magnetic fields in the real situation and the lab simulation are different enough that there may be some confusion based on which situation the writers of the paper are talking about. This may account for some of the confusion about the bow shock origin of the X-rays.

It's also important to keep in mind that there may be more than one source for the X-rays.

There is only one other source for the X-rays and that's K-transitions after an electron is knocked out of the K-shell of an atom and electrons in higher shells replace it.

The reference in Fig. 5 doesn't say the bremsstrahlung contribution is *always* minimal; it says quite clearly it's minimal *if there are no hot electrons.*


True. However, the authors are using the conditions at the bow shock to create the waves which cause the x-ray emission. If the x-rays are being seen well inside the bow shock, then that is a problem....[cont]
cantdrive85
1 / 5 (1) Mar 19, 2018
It was a bit of a surprise when they first detected them in '96 at Hyakutake.

Failure of model.
In retrospect, it should have been predictable. I guess nobody thought to look, until then.

LOL, convenient isn't it? Plasma ignoramuses, as I have been saying.
The x-rays have specific signatures which shows that they come from charge exchange reactions between the solar wind heavy ions, and cometary neutrals

A type of electric discharge, the electric comet lives!

Let me fix your statement to reflect facts;
"We've just had a two year mission to a comet. The only pseudoscience that got shot down was the idiotic, hypothetically based dirty snowball comet woo."
http://www.lunart...ball.jpg
Failure of model.
Reality;
http://sci.esa.in.../?t=1012
No snowball present.
jonesdave
3 / 5 (4) Mar 19, 2018
[cont........].......another problem, which they don't reference, and which matches the CX explanation far better, is the observations by Chandra and SWIFT of the impact at Tempel 1. They see little or no x-ray prior to the impact, and for a few seconds after the impact. However, the x-rays then start to rise, and this is explained as the freshly released H2O vapour CXing with the SW.
As the authors of a paper linked below, say:

In fact, one of the key science results to come from the Deep Impact experiment is the verification of the CXE mechanism as driving cometary X-ray emission using multiple lines of evidence.


Chandra observations of Comet 9P/Tempel 1 during the Deep Impact campaign
Lisse, C. M. et al.
http://ftp.astro....2007.pdf
Da Schneib
5 / 5 (1) Mar 19, 2018
Hmmm, maybe I misspoke. There is another mechanism for X-ray emission: charge transfer between heavy ions in the solar wind and the neutral cometary atoms in the tail. This is detailed in an old paper (now open access by Wiley at https://agupubs.o...6GL03780 choose the PDF button). This paper is referenced in the Rigby et al paper. Note that the emission zone for this process is some 100,000 km from the nucleus of the comet, however, so these will be relatively easily differentiated from the K-shell and bremsstrahlung processes which are very much closer to the cometary nucleus.
jonesdave
3.4 / 5 (5) Mar 19, 2018

No snowball present.


Idiot. Why are you linking to ancient photos? Whipple came up with his hypothesis in the 40's. We'd never seen a comet! We've known since Halley that they are dark, you loon. And have plenty of ice. And no rock. And no electric discharges. Please show me where the idiot Thornhill predicted CX reactions. In fact he dismissed it, and wanted some sort of electric woo from EDM (lol)!

https://apod.nasa...104.html

Da Schneib
5 / 5 (2) Mar 19, 2018
BTW, in case you missed the post, @jones, I share your lack of conviction in this paper, for different reasons than yours. I think some further laboratory investigation is needed in conditions more similar to the real world case of a comet.

But I think the analysis in the paper of the cometary case is fairly good and expect to see both the K-shell and bremsstrahlung processes substantiated; it's a fairly good argument, though not as well supported by the lab work as the authors seem to think.

Regarding the Deep Impact mission, I will point out that the direction of the bremsstrahlung is a fairly tight beam, so if the mission didn't fly through it they might have missed this.
jonesdave
3 / 5 (4) Mar 19, 2018
Hmmm, maybe I misspoke. There is another mechanism for X-ray emission: charge transfer between heavy ions in the solar wind and the neutral cometary atoms in the tail. This is detailed in an old paper (now open access by Wiley at https://agupubs.o...6GL03780 choose the PDF button). This paper is referenced in the Rigby et al paper. Note that the emission zone for this process is some 100,000 km from the nucleus of the comet, however, so these will be relatively easily differentiated from the K-shell and bremsstrahlung processes which are very much closer to the cometary nucleus.


Yeh, I'm not sure about the tail, have to have a look, but Lisse and others saw the first indication at Hyakutake in '96 as a crescent shaped feature in the sunward direction. I'm guessing that all you'll get down the tail is already picked-up, ionised cometary species. Anything still neutral is just going to keep on heading out, sunward.
jonesdave
3 / 5 (4) Mar 19, 2018
Regarding the Deep Impact mission, I will point out that the direction of the bremsstrahlung is a fairly tight beam, so if the mission didn't fly through it they might have missed this.


I don't think the DI spacecraft could have detected the x-rays. Chandra and SWIFT did those measurements. I believe XMM-Newton also had a gander. However, their observations would have covered a large area around the comet.
Da Schneib
5 / 5 (2) Mar 19, 2018
From the paper, I'm getting the impression of a fairly tight beam due to the direction of the emitted "hot" charged particles and the vector of the solar wind B field. Remember that the effect the authors are discussing is v x B (for lurkers, that's velocity of the hot charged particles, cross the solar wind B field; in this case x is not the ordinary multiplication product but the cross product appropriate for vectors).
Da Schneib
5 / 5 (2) Mar 19, 2018
Oh, and @RC, keep in mind as well that comets don't make magnetic fields. For the v x B product to be meaningful, then, the solar wind B field is the only one that means anything since there is no other. B is the designation for the magnetic field in the Maxwell equations.
Da Schneib
5 / 5 (3) Mar 19, 2018
And a suggestion, @RC: it's fine to speculate, and it's fine to be wrong when you speculate. I speculate and am wrong quite often. But I always label it as speculation and I don't come along and attempt to pretend I was "right all along" later with specious arguments involving magic radiation from nowhere and misuse of terminology like you do. It's this practice that makes people vote you 1s and peck you to death. You might want to think about that.
jonesdave
3 / 5 (4) Mar 19, 2018
Hmmm, maybe I misspoke. There is another mechanism for X-ray emission: charge transfer between heavy ions in the solar wind and the neutral cometary atoms in the tail. This is detailed in an old paper (now open access by Wiley at https://agupubs.o...6GL03780 choose the PDF button).


Ahh, that paper. Yes, this was the initial report of the findings, which were unexpected at the time. I'm surprised they referenced it, as the mechanism was unsure then. However, there has been a fair bit of observation since then, as well as modelling. They do reference a modelling paper, which I haven't read yet. However, I think the CX mechanism is pretty much a slam dunk, given the line emission, and the good fit of the models, not to mention the Tempel 1 observations.
I'll have to have a search around. I know lower hybrid waves are seen at comet 67P, but they got nowhere near the bow shock. I'll have to have a look at the Halley papers.

cantdrive85
1 / 5 (1) Mar 19, 2018
Charge exchange is electric discharge, that is one aspect of an electric comet.
Why are you linking to ancient photos? Whipple came up with his hypothesis in the 40's

Yep, and that's your model jackass. Nothing changed until the mid-80's when it was falsified. The dirty snowball BS is why no one thought to consider x-rays.
We'd never seen a comet!

But that is what the guess states it should look like. Ya know, a prediction. It was an ultimate fail.
jonesdave
4 / 5 (4) Mar 19, 2018
Charge exchange is electric discharge, that is one aspect of an electric comet.
Why are you linking to ancient photos? Whipple came up with his hypothesis in the 40's

Yep, and that's your model jackass. Nothing changed until the mid-80's when it was falsified. The dirty snowball BS is why no one thought to consider x-rays.
We'd never seen a comet!

But that is what the guess states it should look like. Ya know, a prediction. It was an ultimate fail.


No, idiot, CX is not an electrical discharge. Hell, it is happening due to water molecules that the idiot Thornhill said weren't there! And no, nothing has been falsified. Comets are dust and ice, as predicted by Whipple. I'm not sure where the photo comes from, but Whipple predicted a surface of 'metoritic material'. Dust.
jonesdave
3 / 5 (4) Mar 19, 2018
OK, let's see what the idiot Thornhill said in 2006, when we already knew the x-rays were from CX:

Most of the voltage difference between the comet and the solar plasma is taken up in a double layer of charge, called a plasma sheath, that surrounds the comet. When the electrical stress is great enough, the sheath glows and appears as the typical cometary coma and tail. Diffuse electrical discharges occur in the sheath and at the nucleus, radiating a variety of frequencies, including x-rays.


What voltage difference? None seen. Double layers? Where was this found? Hasn't been. What electrical stress? What the hell is 'electrical stress'? He's talking out of his arse, as usual. Been through the whole crappy pdf. Nothing about CX between solar wind heavy ions, and the water that he says isn't there. Which we find in abundance. The guy is a nutjob.

http://thunderbol...omet.pdf
jonesdave
3 / 5 (4) Mar 19, 2018
Another pearl of wisdom from the moronic leader of the Lightning Bolt Cult:

In the electric view, there is no real distinction between a comet and an asteroid, apart from their orbits.


Dear me! And some people take this loon seriously! Ever heard of asteroids on elliptical orbits, Wal? Guess what they don't do? What about comets in low eccentricity orbits, Wal? Guess what they do?
cantdrive85
1 / 5 (2) Mar 19, 2018
I'm not sure where the photo comes from, but Whipple predicted

That's Whipple, hugging his creation. That's his failed guess.
CX is not an electrical discharge.

This coming from the guys who claims; the magnetic fields will persist long after the electric current is removed"...LOL
https://www.ameri...ctricity

You and da schnied are two peas in a pod, between his magnetic monopole and your magical magnetism you could start a whole new "science". Since it is based in pseudoscience, just like Einstein's faerie tales, I think calling it General Magnetivity would be highly appropriate. General Magnetivity is the perfect name for your "science"!
jonesdave
3 / 5 (4) Mar 19, 2018
^^^^^^^Sorry, but your idiotic model failed. And Thornhill never predicted CX, even though it was already known by then. If you think he did, then show me.
And Whipple (and I doubt you've ever read his papers) was a bloody sight closer to what a comet is in the 40's, than the Velikovskian idiots who wrote that pdf were in 2006! So what does that say about the aforementioned idiots?
jonesdave
3.4 / 5 (5) Mar 19, 2018
This coming from the guys who claims; the magnetic fields will persist long after the electric current is removed"...LOL


So what is the measured current in the solar wind? Hint; four letter word beginning with 'z'.

cantdrive85
1 / 5 (2) Mar 20, 2018
What voltage difference?

You have already acknowledged electrostatic charging of the surface, there is a voltage difference right there jackass.
None seen. Double layers? Where was this found?

The bow shocks are double layers, the multiple layers in the coma are double layers. Send the MMS mission to a comet and we'll see what we see.
Ever heard of asteroids on elliptical orbits,

http://earthsky.o...oid-288p

https://en.m.wiki...eristics
Weird! Electric comet stronger everyday.
cantdrive85
1 / 5 (2) Mar 20, 2018
And Thornhill never predicted CX

After you posted;
Most of the voltage difference between the comet and the solar plasma is taken up in a double layer of charge, called a plasma sheath, that surrounds the comet. When the electrical stress is great enough, the sheath glows and appears as the typical cometary coma and tail. Diffuse electrical discharges occur in the sheath and at the nucleus, radiating a variety of frequencies, including x-rays.

That last sentence is the one to pay attention to, there is your CX. The plasma sheath he refers to in the first sentence is the coma. Even the basics are above your head.
jonesdave
3.4 / 5 (5) Mar 20, 2018
The bow shocks are double layers, the multiple layers in the coma are double layers. Send the MMS mission to a comet and we'll see what we see.


We've just had a spacecraft at a comet for 2 years, or did this pass you by? NO double layers. Spacecraft at Halley flew through the bow shock. NO double layers. No electric woo. No rock. No voltage differential. A diamagnetic cavity, with no possibility of idiotic EDM (lol) happening. The electric comet woo was a complete failure.

jonesdave
3.4 / 5 (5) Mar 20, 2018
That last sentence is the one to pay attention to, there is your CX. The plasma sheath he refers to in the first sentence is the coma. Even the basics are above your head.


Errrr, no, idiot. The DL is what we are looking at, and the non-existent voltage differential to drive his non-observed electric woo. He didn't predict CX. He couldn't, as it was already frigging known about. Show me this electrical woo, such as EDM (lol) that wasn't observed. Or the rock that wasn't observed. Or the impossible manufacture of OH from the solar wind, etc, etc. Like I said, the idiot's model has failed, and only other idiots still believe in it.

jonesdave
3.4 / 5 (5) Mar 20, 2018
According to the Velikovskian loon:

When the electrical stress is great enough, the sheath glows and appears as the typical cometary coma and tail.


What electrical stress? What sheath is glowing? Doesn't the idiot realise that what is 'glowing' is sunlight reflected from bloody dust! How thick can you be? You think a spacecraft with a suite of plasma instruments is going to miss this non-existent 'glowing', whatever the hell it is supposed be? The bloke is a complete loon.

cantdrive85
1 / 5 (2) Mar 20, 2018
What electrical stress? What the hell is 'electrical stress'?

Like I said, the basics.
https://en.oxford...c_stress
It's been in the scientific literature/lexicon since the 19th-century. ROTFLMAO! New levels of stupidity are exceeded everyday jonesdumb!
jonesdave
3.4 / 5 (5) Mar 20, 2018
What electrical stress? What the hell is 'electrical stress'?

Like I said, the basics.
https://en.oxford...c_stress
It's been in the scientific literature/lexicon since the 19th-century. ROTFLMAO! New levels of stupidity are exceeded everyday jonesdumb!


So where TF is it, dummy? You know, measured? Nothing in two years, you prawn. Just as bloody invisible as his rock and his DLs and his EDM (lol). I don't care how you define it. It wasn't there. Just ice, and vapour and dust. No woo.
jonesdave
3.4 / 5 (5) Mar 20, 2018
It's been in the scientific literature/lexicon since the 19th-century. ROTFLMAO! New levels of stupidity are exceeded everyday jonesdumb!


At least I know what a collisionless plasma is, eejit.
cantdrive85
1 / 5 (2) Mar 23, 2018
The lid has officially been closed on the dirty snowball pseudoscience. Dead in the water ice...

https://youtu.be/aoVWuRo6D9Y
RealityCheck
1 / 5 (2) Mar 26, 2018
@Da Schneib.
it's fine to speculate, and it's fine to be wrong when you speculate. I speculate and am wrong quite often. But I always label it as speculation and I don't come along and attempt to pretend I was "right all along"...
Please first go read link: https://phys.org/...644.html
It shows I was correct in using "synchrotron radiation" term to describe such spiraling-electron X-ray etc radiations in astrophysical context. And as for 'speculating'; I try NOT to when the known science/logics allow direct/reasonable 'reminders/extrapolations' (such as I posted earlier for your own consideration).
keep in mind as well that comets don't make magnetic fields.
I never said they did, DS. I merely pointed out the possible causes of them arising in the SW-impact/stagnation-zone plasma/fast-electron contexts which create their own localized dynamical plasma/charge flow system for the duration of said comets' SW transit times. :)

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