Twin tails

Amateur and professional astronomers alike have been monitoring changes in Comet 67P/Churyumov-Gerasimenko’s tail, which, since December, has been exhibiting two prominent structures.

Image of 67P/C-G obtained with the 2.5m Isaac Newton Telescope on La Palma on the morning of 19 January 2016. The picture was taken through a red filter; the apparent colour has been added to help pick out faint structures by eye. The tail extends 0.5 degrees from the nucleus (the apparent size of the full moon) before reaching the edge of the image, corresponding to a minimum length of 2.2 million km. Note that the black lines are gaps between CCDs in the array (the camera has 4 CCDs to cover half a degree).Credit: Alan Fitzsimmons / Isaac Newton Telescope

Image of 67P/C-G obtained with the 2.5m Isaac Newton Telescope on La Palma on the morning of 19 January 2016. The picture was taken through a red filter; the apparent colour has been added to help pick out faint structures by eye. The tail extends 0.5 degrees from the nucleus (the apparent size of the full moon) before reaching the edge of the image, corresponding to a minimum length of 2.2 million km. Note that the thick black lines are gaps between CCDs in the array (the camera has 4 CCDs to cover half a degree). Credit: Alan Fitzsimmons / Isaac Newton Telescope.

“Current indications from the data we’re collecting of Comet 67P/C-G is that both features are dust structures,” says professional astronomer Alan Fitzsimmons, who has recently spent time observing the comet with the Isaac Newton Telescope in La Palma.

Multiple tail structures are not uncommon in comets, and indeed have been observed during previous apparitions of Comet 67P/C-G.

The two portions of the tail are attributed to different populations of dust grains swept away from the comet’s nucleus by the radiation pressure of the Sun over the course of its 6.5 year orbit around the Sun.

In the image above, taken with the 2.5m Isaac Newton Telescope on La Palma, the upper ‘streamer’ is precisely aligned along the projected orbit of the comet, implying it is made of large and/or old dust grains moving slowly along the orbit of comet. This part is called a comet dust trail because it is formed from the particles trailing along the path of a comet. This dust trail of Comet 67P/C-G has been seen several times before by both ground-based telescopes and space-based infrared observatories.

The lower portion of the dust tail exhibits a thin central core and resembles a feature called a neckline structure. This is formed from dust grains released on the “opposite side” of the orbit from the time of the observation, and all lining up as seen from Earth. This has also been seen before in previous returns of Comet 67P/C-G.

“We need to do more calculations and modelling, but if our interpretation is correct, then the dust grains forming the neckline in December 2015 were ejected from the comet nucleus around March last year, prior to perihelion,” says Alan.

The dust coma can also be seen all around the comet nucleus, with a peak extending just ahead of the comet, and with a broader tail of smaller dust grains swept out below the neckline.


The amateur community is also acquiring regular images of the comet.

“Because the large telescopes have nowhere near the time-coverage that the amateur/pro-am community have, it’s fantastic to see the amount of valuable data people are collecting,” adds Alan.

For example, the images shown left were taken by Tony Angel and Caisey Harlingten through a 4” telescope of the Searchlight Observatory Network at the Observatorio Sierra Contraviesa, Spain, on 22 December 2015. The image was made by stacking six images taken with an exposure of 300 seconds each in order to bring out deep details of the faint, extended tail structures.

The image is shown in positive (top) and negative (bottom).

Credits: SON@OSC/T. Angel & C. Harlingten.


Astronomer Damian Peach has also been keeping a regular eye on the comet as it moves across the sky. The colour composite below captures the comet between September and November last year, showing the comet’s tail and its fuzzy coma. (Click here for an image taken more recently by Damian, on 18 January.)

Comet 67P/C-G between September and November 2015 seen in six LRGB images acquired with a 24" CDK telescope with FLI camera by Damian Peach. Each section is composed of 8 x 120 second exposure images. During this time, the tail is estimated to measure around 20–30 arc mins. Credit: D. Peach.

Comet 67P/C-G between September and November 2015 seen in six LRGB images acquired with a 24″ CDK telescope with FLI camera by Damian Peach. Each section is composed of 8 x 120 second exposure images. During this time, the tail is estimated to measure around 20–30 arc mins. Credit: D. Peach.

“Collecting data from Earth while Rosetta is flying alongside the comet is providing a unique and complementary dataset that will help both Rosetta mission scientists and ground-based astronomers understand processes relating to the comet’s activity at a range of scales,” says Rosetta project scientist Matt Taylor. “We’re hoping that ground based images will continue to be obtained until later this summer when the comet gets fainter and too close to the Sun in the sky to observe.”

Astronomers wishing to contribute to the imaging campaign of Comet 67P/C-G can find out more here.

Read more about the amateur observing campaign in our blog post here, and keep up to date with latest images from the PACA (Pro-Am Collaborative Astronomy) project community here.
Read more about the professional observing campaign in recent blog posts here and here.

Update 3 March:
Read more on the JPL website in “Contributions of amateur observers in support of ESA/Rosetta mission from 2014-2016




  • logan says:

    Beauty in Science. Thanking Professional and Amateur Teams and Individuals on sharing their work.

    On adding to the tails vectors is the axis of the impact bow on the solar wind.

    Intrigued on the changing colors on Damian Peach work. Maybe observational variances.

  • THOMAS says:

    Can anyone kindly point us to previous observations of diverging *dust* tails and to corresponding studies on their origins and the physical processes thought to be at work – I haven’t found any such work myself. (The only reference I found on Google when I typed in “multiple tail structures” was in relation to bacteria and/or viruses).

    To put my skepticism of the standard account another way:

    Young Chury, it seems, sports two tails
    Made of dust, both, on diverging trails.
    Did the experts expect
    Such a barmy effect?
    Or is it their theory that ails?

    • emily says:

      Hi THOMAS,
      Did you follow the links hyperlinked in the text for the previous observations for 67P? and and references therein should help for a more detailed follow-up.

      • THOMAS says:

        Hi Emily,
        Actually, it was precisely because I found nothing in either link to account for the double dust-tail phenomenon that I posted my request for pointers to other studies. If indeed “multiple tail structures are not uncommon in comets”, there must surely be many other studies on the subject, (and not just on 67P) which address the mechanism supposed to be causing the phenomenon.

    • Harvey says:

      I had a pretty good dig around in the big academic databases & no, couldn’t find anything directly on this. There are some very old papers with slightly vague titles which might do so, but too old for easy full text access. Plenty on the distribution in normal single tails. Maybe I missed it, didn’t hit quite the right search terms; I got a lots of false hits too!

      Clearly they have more detailed work to do, but the explanation seems broadly credible. The spectra will be diagnostic of it being a dust as opposed to an ion tail – even filter results would be strongly indicative.

      • THOMAS says:

        Thanks for looking, Harvey, and for your honesty in reporting the absence of any real result. I simply wonder if the problems you’ve had coming up with anything more conclusive might not be indicative of a dearth of prior observations on this point coupled with a serious lack of explanatory power on the part of the standard theory. I don’t doubt your searching skills…

        I would simply take issue with your idea that “the explanation seems broadly credible”: firstly because it’s not so much an “explanation” as a mere “description”; and secondly because a so-called “explanation” which only “seems broadly credible” does not strike me as being that scientifically sound. Allow me to add a second verse to my limerick on the subject:

        They search high and low, but in vain,
        For papers and facts to explain
        The dust-trails observed
        Without seeming absurd,
        The truth, clearly, is not all that plain…

        More precisely, how could simple gravitational sorting by dust-grain size in any way cause these two distinct dust-lanes? Are we to believe that 67P only throws off dust of two different calibers and/or that these two discrete populations are somehow channeled into two distinct trails? If it’s the so-called solar “wind” that’s doing the sorting, how does that work precisely (which particular property of the solar “wind” takes care of the sorting?) And if dust of intermediate caliber is also being produced, as seems extremely likely, where is that dust going without being particularly visible, and why? Every new surprising observation of 67P, whether by Rosetta, Philae or, now, ground-based facilities, only serves to pose far more questions to standard theory than it solves.

        • Harvey says:

          As I said, broadly credible, but I’d want to see a full scientific paper before reaching a firm view. This is just a preliminary view expressed in this blog, a long way from that.

          A bimodal distribution of dust particle sizes would be nothing particularly outrageous; but yes it would need a more detailed explanation. This would not get past referees as it stands. But it’s not intended to.

          If someone comes up with a better explanation, fine.

          Yes, I do have considerable experience in searching academic databases, and I have access. But some searches are just intrinsically tricky, because of the nature of the terminology used, usage of words in other fields, etc etc. It can be difficult to find the wheat in the (for our purposes) chaff, and this was such a case.

    • martin says:

      Chapter 7 “Dust Tails” in K.S. Krishna Swamy’s book “Physics of Comets’ shows a picture of all kinds of dust tail behaviours (Fig. 7.6, which is taken from the book “Comets in the post-Halley era” eds. Newburn et al. 1991)

    • Kamal says:

      Would be grateful for some one with tail dynamics knowledge to clear up some points.

      “The upper streamer is precisely aligned along the projected orbit … made of large/old dust grains moving slowly along the orbit of the comet”. David Jewitt also says regarding Type II dust tails that the particles have slightly less gravitational attraction to the Sun than the nucleus.
      Because the tail points away from the Sun, the orbit is projected, the nucleus has not reached there yet. So how did the large/old grains get there?

      67p has made only a few (say, under ten) revolutions in this orbit, so it seems unlikely that these grains remain from a previous pass.

    • Kamal says:

      Ah, I think I get it. The trail is made of particles ejected from the comet with almost the comet’s orbital characteristics, pushed away by radiation pressure, hence less net attraction. Does “earlier” mean well before perihelion? In the previous pass? The post says that the neckline particles are also from before perihelion.

    • Kamal says:

      Benefited from reading “Motion of cometary dust” by Marco Fulle (pdf available on the net), especially Section 7 regarding the neckline.

      • THOMAS says:

        Two points, Kamal:
        -the most recent reference cited in the article you quote dates from 2002. No further comment needed.
        -the article sheds absolutely no light on the DOUBLE dust-tail phenomenon which is the new breaking news from 67P we’re discussing. So how does it help?

        • Harvey says:

          The fact that it is from 2002, or indeed any previous date, is absolutely not a good reason to ignore it.

          Rosetta has brought us a wealth of information, unique in its detail of near-comet conditions. But only of 67P, comets differ, and not of the distant tail conditions relevant to this discussion.

          Older data may have limitations, which need to be understood and recognised.
          But they most certainly cannot be validly ignored.

      • Kamal says:

        Thomas: The Fulle article gives an explanation even though it seems to be written around 2003. In fact this is a review article and the explanation comes from earlier. See the discussion on comet Arend-Roland which was seen with a striking anti-tail in the 1950s, which is explained here as a neckline feature. The beautiful thing about the 67p photograph is how clearly it illustrates these phenomena.

  • originalJohn says:

    Interesting exceedingly remote interpretation by Alan Fitzsimmons of the structure of the comet tail. It would be more interesting if it could be supported by analysis of the tail by the Rosetta craft which is actually there. Things such as ion composition and proportion, neutrals proportion and dust composition, particle size and charge state. The tail is somewhat unusually collimated to pencil thin beam over millions of kilometres. Is this attributed entirely to the solar wind or has any other possibility been considered. ie What is the collimating mechanism.

    It always strikes me as interesting too how readily it is accepted that the illumination of the comet is all down to light reflected from the Sun. When you look at it it has the appearance of an intrinsically illuminated object, like the stars that surround it in the image, particularly in the spherical head region of the coma.

    • emily says:

      For info: there’s a plan for Rosetta to do a far excursion from the nucleus in order to visit the tail region ~700 km ‘down tail’ for around 2 weeks in the March/April timeframe.
      We’ll get some more details about that nearer the time to confirm what is planned.

      • originalJohn says:

        Thanks emily. I look forward to the results of that.

      • Kamal says:

        Emily: Three risks here.

        1) Rosetta gets hit by a large boulder thrown out by 67p and is lost.

        2) A Rosetta instrument gets hit by a small dust particle and is lost.

        3) Startrackers get confused.

        Would like to know how the excursion plans to minimize these difficulties.

        Regards, Kamal

        • emily says:

          I think it is fair to say that these types of risks are faced every day of the mission!
          But I will be sure to follow up on any specific safety concerns relating to the tail excursion, nearer the time…

        • Kamal says:

          Emily: suitably chastened! yes, I forgot about everyday dangers.

      • logan says:

        As separation between dust tails keeps a constant departure speed, Then must be related to constant[s] on the dust populations themselves. Not related to a shared environment.

        One of the tails separate completely from the ion envelope. Neutral dust tail?

        Just speculating.

        • logan says:

          The one inside the ion envelope strongly collimated. The tail outside of the ion envelope doesn’t collimate..

    • ianw16 says:

      Dust is more dense in the vicinity of the nucleus. Hence it is brighter. The particles become more diffuse as they spread out behind the nucleus, therefore less bright.

    • Gerald says:

      Originaljohn, usually there is a ion tail and a dust tail. The ion tail shows some “intrinsic” brightness from excited ions. A dust tail(s)’ “intrinsic” brightness might be defined in the infrared representing the black body radiation of the dust.
      The light emitted by excited atoms/molecules/ions can be distinguished from reflected solar light and from black body radiation by spectrography.

      Besides solar wind, sunlight acts on dust grains by excerting radiation pressure:

    • martin says:

      I guess the important part of the claim is “has the APPEARANCE”

      • originalJohn says:

        No claim martin. An observation.

      • originalJohn says:

        Yes Gerald despite centuries of investigation and interpretation the straight forward question remains. Is the light we see coming from a comet mainly a reflection of the Sun’s light from dust or is it intrinsic emission by the comet coma. I would not deny the possibility of some dust reflection but the presence of intense clearly defined emission peaks in the optical frequency range, that are not in the solar spectrum, means that the comet is emitting intrinsic light which has nothing to do with the Sun. It is misleading therefore to categorize comet light as only reflected light. This would apply to the jets too, which are the source of the coma.

        • Gerald says:

          Originaljohn, ultraviolet light from the Sun can excite or ionize neutral atoms and molecules. When returning to the ground state or recombining, they emit photons, some of which in the visibile spectrum.
          Without sunlight, these emissions cease almost.
          Regarding intensity, integrate the refelected light over the wavelength, and integrate separately over the peaks from emitted light.
          You’ll see, that in the presence of dust or the solid surface of the comet, the reflected light is much more intense than the fluorescent light.
          So in the dust jets it’s barely possible to see the “intrinsic” light on top of the reflected sunlight in a usual photograph. You might see it in spectra.

          It’s different in almost dust-free regions of the comet’s ion tail. There the emitted visible light from excited atoms and molecules takes the major part of the visible light. In color photographs you see the according colors typical for the excited gas species.
          This typical colors are missing when looking at the illuminated surface of the comet. It’s almost perfectly grey. Sublte color variations of the surface are mostly due to composition. They may also be caused by grains of the size near the wavelength of the light (structural colors).
          There might then remain a tiny resudual color caused by light emission of ions. But you certainly cannot see these subtleties when looking at a NavCam image. And it will be very difficult at least, even for calibrated OSIRIS images of the surface of the nucleus, or for dust jets.

    • Sovereign Slave says:

      The “pencil thin” dust beam IS extremely striking and apparently has not been explained. It does seem to smack of something collimating the dust to maintain such a tight organization over such a long distance. The simple explanation is that whatever is collimating the dust jets at/near the comets surface is the same force that is collimating the pencil. Otherwise you’re left with having to explain two separate mechanisms for the same type phenomena produced by the same comet, though the scale is of course different.

      • Kamal says:

        SS: Has been explained, please see my reference to the Fulle 2003 article above. There may be other explanations too, I am not an expert, I have only read one article.

      • logan says:

        Agree, SovereinSlave. About those strongly collimated jets seen at arrival epoch 🙂

  • Harvey says:

    Just looking at it tells you very little.
    But the spectrum is diagnostic.
    Of relevance:
    Dust tail of the active distant Comet C/2003 WT42 (LINEAR) studied with photometric and spectroscopic observations
    By:Korsun, PP; Kulyk, IV; Ivanova, OV ; Afanasiev, VL ; Kugel, F ; Rinner, C ; Ivashchenko, YM
    ICARUS Volume: 210 Issue: 2 Pages: 916-929 DOI: 10.1016/j.icarus.2010.07.008 Published: DEC 2010
    Relevant extract from the abstract:
    “At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet.”

    • originalJohn says:

      Thanks Harvey. I had trouble getting the Chinese abstract but plenty of other similar publications in the same search. On looking through a few the conclusion ” the comet did not reveal molecular emission features above the reflected continuum” is a common one. All of these observations were made at typically 4-6 AU distances ( incidentally beyond the snowline) and it strikes me that the absence of specific cometary emissions could be more to do with the signal to noise ratio, with the comparatively weak cometary signal lost in the general noise. Are you aware of any spectral comparisons between comet light and sunlight when the spectrometer is close to the cometary source. I appreciate it is not easy to get near a comet but certainly earthbound observations within 1 AU are possible. Of course the Rosetta team do not have to worry about AUs, they are there with their spectrometers. I do not recall having seen as yet a spectral comparison from them between the comet emission and the solar continuum.

      • Harvey says:

        The distance of the spectrometer to the comet only matters in signal to noise terms as you say.
        But in the presence of a reflected continuum, the noise rapidly becomes dominated by the photon statistics noise (Poisson noise) of the continuum, not by the noise of the detector itself. This means the advantages of being close are less than you might think with regard to
        One improves linearly, the other as the square root of signal level.detecting molecular emission against a continuum, limited by saturation.
        Different for an ion tail, where it is molecular emission against a dark background.
        No, I’ve not seen them explicitly publish that. I’d guess its back in old literature. Since there is no expectation it would be other than a reflected continuum (as modified by the comet colour) I doubt anyone would bother to publish a paper saying ‘look, its just the reflected continuum….’ I’m sure they would publish if it *wasn’t* that however; that would be interesting.

        • originalJohn says:

          Thanks for your comments Harvey. My own investigation of the published data has shown that typically the optical spectra of comets do not match that of the Sun. I am sure you could find the same data if you looked. A match would require peaks of the same intensity at the same wavelengths. This does not occur. The comets produce characteristic optical spectra ( unless their signal is too weak and lost in the noise) showing that they are emitting intrinsic light. It looks as though the reflected light claim is an assumption.

          • Harvey says:

            The crucial issue is whether it is a continuum or line spectra.
            The ‘continuum’ (which does have some structure) will be modified by the ‘colour’ of the material, and by the varying scattering coefficient with wavelength for small particles. An exact match is not expected; typically from the dust tail.

            Lines on the other hand are indicative of atomic and molecular emission, and will typically come from the ion tail.

            I haven’t seen anything thart looked like a ‘problem’; broadly, the dust scatters solar spectrum, the ion tail emits.

  • Ramcomet says:

    Two tails is not new, most comet’s exibit this since I became an aneratuer astronomer.

    Collimation is not new, if you think of photons increasingly bouncing off of sparce molecules surrounding the tails, as distance increases, the solar wind should have an imcreasingly constraining, focussing pressure effect upon both dust and ion tails.

    What is so i teresting to me is the CURTAIN of “falling” dust, being left below (especially seen in the negative image), as 67P’s diaphanous and highly elliptical solar disc, that is perpendicular, or beimg gently “airbrushed”, falling like lace, 90° from the dust tail.

    This left-behind curtain of all comets is the source of of Earth’s meteor showers. Bit, a real pity we won’t be able to enjoy this comet’s falling stars! Outside of our orbit.

    If we could, we would forever be reminded of Philae and Rosetta’s epic adventures every six plus years, immortally!

    • Ramcomet says:

      Sorry for all the typos, but hope you at least “get the drift”!

    • Sovereign Slave says:

      “Collimation is not new, if you think of photons increasingly bouncing off of sparce molecules surrounding the tails, as distance increases, the solar wind should have an imcreasingly constraining, focussing pressure effect upon both dust and ion tails.”

      Not sure how much you’re speculating about processes, Ramcomet, but one does have to wonder what other force there is that far from the comet that would be capable of collimating it’s dust besides the solar wind. I can imagine Harvey and Gerald running down the list of reasons why the solar wind would not be able to account for the dust jets near the comet collimating, but still, what’s good for the goose…

      • Gerald says:

        Radiation pressure is likely the strongest driving force accelerating the dust. This force points radially away from the Sun. Without initial velocity relative to the comet, this radiation pressure would drive the grains on a straight line away from the Sun. No additional collimation needed.
        This explanation works best for small dust grains.

        But nature is rarely that simple. So you have initial velocity, and dust grains are electrically charged with a few volts. The charge may vary from grain to grain, including the sign of the charging. This might cause an overall attraction within the dust tail, and contribute to the collimation.

        There may well be other effects I didn’t consider.

        • Ramcomet says:


          Oh yes I admit huge speculations, then get the wonderful benefit of great scientific minds to support or throw them out on this wonderful blog. Thanks to you all.

          By radiation pressure, Gerald and SS, I was imagining lighter concentrations of dust in the outer portions of the tail reflecting photons from the sun in all directions, which might add a weak constraining pressure effect upon the main inner part of the tail.

          Also, the inner portions of the tail are more shaded from the sun, so those particles are not moved in all directions as much as the outer particles. This might have a weak constraining or collimating effect?

          This is Cometary Daydreaming, of course!

          As a toy designer, I once challenged myself to come up with a “safe for toy regulations laser beam”.. First I tried a toy grade 20 degree lensed LED, the most focussed I could find, then attached a “collimating nozzle” by rolling up a tube of mirror mylar and shaping it so it was smaller at the far end. That was my first intuition and it didn’t work.

          What did work, at least well enough to project a one inch dot of red light on the wall at fifteen feet away, (good enough for my Toy “spotting laser” Gun anyway!), was the opposite.

          Further tuning found success: A 2 degree angle of the mylar tube with the larger aperture on the far end away from the LED source tended to straighten out all the different photon angles into a beam I needed. (I think this feature was patented by our company)

          This made me think that here, maybe there is a similar collimating effect on the comet’s dust tail, but substituting stray random-direction photon pressure off outer tail particles from “dust glow”, instead of my mylar tube?

          Cometary Daydreaming again. 😉

          • Gerald says:

            Interesting ideas, Ramcomet.
            Those suggested mechanisms might be at work for a sufficiently dense dust cloud with ambient light as the major source of light.
            I wonder whether it could work with an almost point light source like the Sun. The key might be the “almost”.

          • Harvey says:

            Umm. Sounds dangerously as if it contravenes a rather basic law of optics, conservation of brightness, but maybe I haven’t understood fully what it was.
            In other words the divergence of a source multiplied by its area is a constant, or increases, in any classical optical system. Think of binoculars say.
            (‘Brightness’ here has a specific technical meaning, not its colloquial meaning.)

          • Gerald says:

            The subtle question is, how is the dynamical behaviour of a dust cloud, if a distant light source of some apparent area, radiation pressure, light scattering and absorption are the main ingredients. Can there occur collimation?
            I’d think the cloud would mainly be driven radially away from the light source.
            Would it get more fuzzy or more collimated on its way by partial shadowing of the central region of the cloud, if the apparent area of the light source is non-zero?

  • logan says:

    Logan has been systematically abusing the term ‘trailing’.

    Time to set. Classical -viscous- trailing could only happen inside 67P, at surface departing and within outbursts.

    But there is another kind of trailing [acting on the distance]. That one that ends carefully ‘blending’ the charges within Solar Wind. Not knowing its name please allow me to call it ‘charge trailing’.

    [Martin could be smiling about my wanderings -He knows-].

    Everything said below about speed, is related to core frame of reference.

    As Ducky get a quickly accelerating positive ion envelope [blasted by SW], that ends conforming the ion tail, embedded in it is negative dust, not able to quickly accelerate.

    As long as negative dust has not reached the same departing speed of the ion envelope, collimation is going to occur…

    This is just my fiction.

    • logan says:

      Positive dust is going to ‘anti-collimate’. Something a lot wider than neutral dust tail..

  • logan says:

    On extending in ‘charge trailing’.

    This is a mind experiment [know nothing of plasma physics]:

    You can get a pin sharp trail of slow protons just by injecting them in the middle of a non-turbulent flow of fast electrons.

  • OzObserver says:

    Double dust tails have been seen on comets before, ie: C/2014 Q1 Panstarrs, type 2 and type 3 dust tails, visible post-perihelion. What’s strange about that?

  • OzObserver says:

    The pencil-like dust tail doesn’t need explanation other than its an effect of perspective, the dust is spread out in the orbital plane of the comet, as the Earth nears this orbital plane the tail is seen nearly edge on and appears to us to grow more intense as a thin line, its an optical density effect. When the Earth crosses the orbital plane we usually can detect an anti – tail, which is composed of larger particles of dust, take a look at C/2011 L4 Panstarrs images by Rolando Ligustri highlighting this effect as we crossed L4’s orbital plane in 2013.

    • logan says:

      Hi OzObserver, Welcome to the Blog 🙂

      Every theory needs a lot more than one explanation. Your orbital plane argument needs of a third dust tail. Not having access to necessary tools, but speculate that density mapping wouldn’t add up, neither. As for anti-tails, still no idea.

      • logan says:

        ERRATA, Should say: Every phenomenon….

      • OzObserver says:

        It’s not a theory, it’s fact! 🙂

        • OzObserver says:

          There are three types of tail, ion tails are classed ad Type 1, Type 2 is a dust tail made of micrometer sized particles and are usually gently curved, and Type 3 dust tails are made of mm sized particles or larger and result in a more strongly curved tail. Grab yourself a book titled ‘Introduction to Comets’ by Brandt and Chapman, second edition 2004, it has very good descriptions of tail phenomena.

    • Sovereign Slave says:

      This seems like a plausible enough explanation, but in looking through his pics I didn’t see a clear example of the pencil thin dust trail like the one seen above. Could you post a link to a pic showing that, ,and maybe one of his of the dust as seen face on to the orbital plane (so it’s spread out) as well for comparison?

    • logan says:

      Agreeing with you that neutral dust tails ‘draw’ a slight ‘comma’ shape within their orbital plane. Some times perspective could be such that the ‘bow’ of that ‘comma’ shape apparently precedes the core. Seems clear to me that this, is not the case, OzObserver. Maybe I’m wrong, again 🙂

    • Kamal says:

      OzObserver: Am trying to figure the three-dimensional shape of the tail. It is rather broad in the orbital plane, would it be (considering 67P) of the order of thousands of km, perhaps going to hundreds of thousands of km? The jets from the rotating nucleus should create a spreading sphere in the anti-solar direction, would it be of the order of the coma diameter, say hundreds to thousands of km? There are much bigger dimensions in the pictures of 17P/Holmes’s trail by Arto Oksansen at but that was an outburst so presumably not typical.

      • OzObserver says:

        Hi Kamal, The dust in the coma is released in the solar direction, until the pressure of sunlight repels the dust in the anti-solar. The true coma diameter can be found by using [D=2 π Δk Dc / 21600’ ] D= true size of comet’s coma in A.U. ; Δk= comet’s distance from Earth in A.U.; Dc is apparent coma dia in arc-mins. This is a measurement you can use by observing the comet with your backyard telescope. The jets are small scale compared to the coma as visible to us from Earth, this is why we send spacecraft because the coma and or pseudo-nucleus renders the actual nucleus invisible. The structures in the tail are large scale. Some comets have displayed fan-like structures in the coma itself but these are usually only visible in very bright comets. Jets are active when exposed to solar radiation so the dust is ejected at that time due to drag forces from sublimating gases. Keep in mind that the escape velocity is low, and the dust we observe is predominantly in the micron scale. Larger size grains of dust resist the repulsion by sunlight pressure and tend to remain close to the nucleus orbital path for a long time.

  • logan says:

    Felicitaciones a La Palma! 🙂

  • logan says:

    Highly ‘conic’, the impacting bow. Doesn’t it?

    • logan says:

      Thousand[s] km hypersonic shield.

      Tremendous display of kinetic energy drain is having the immediate effect of rounding&shrinking the orbit.

      Somewhere inside this gigantic structure, a little grain of 21 cubic km and (1.0±0.1)×10^10 Tons is vigorously trying to keep its travel, unperturbed.

      On doing so, is expending the same amount of energy than the shield.

      Could feel the tremor under my boots. Could hear the hypersonic boom trough my helmet. Could see the world around me breaking, and departing.

      This is fiction.

      • logan says:

        On coming near to our Sun comets are not ‘cutting’ the Solar Wind.

        Active comets are ‘parachuting’.

        They are variable size little planets..

      • logan says:

        Comets are not playing by Classical Orbital Mechanics.

        Why our resident scientists hadn’t told Us?

      • logan says:

        No point on the indefatigable work of our Sun. ‘Frictions’ with the visitants are a must. Dirty results.

      • logan says:

        The post perihelion comet We are seeing is not dirty. There are not ‘fluffy’, ‘dandelion’ mots of dust ‘gently’ deposited over its surface. There are not ethereal ponds of nothingness where Philae could sink.

      • logan says:

        Its not only the cone of pressure keeping the core inside the shocked coma, but lots of the hypersonic wave being conically focused, and transfered, to the surface.

        Pressure is nominal at both sides of the shocked parabolic coma, but its focusing is precise. If it weren’t, core would not be pushed back and pinch the coma.

        …Shaking this baby Duck. What’s the name of this game, Our resident Scientists?

      • logan says:

        Remember the legend of ancient, horsed warriors, trailing an inflated cape, able to stop, or slow incoming arrows?

        That’s the way a significant amount of kinetic energy energy is transfered from the impact bow to the core, each orbit.

        The resulting difference, on calculating the lost of kinetic energy for a meteoric object the same shape and mass of Ducky, and the lost of kinetic energy for the actually observed 67P -on completing its orbit-, is the percentage of energy actually transfered. From the front shock to the core 🙂

        You can add the photon energy, later.

        Let’s not talk about fields, by now.

        • logan says:

          Almost all this kinetic energy transfer occur at perihelion phase, coinciding with the -less accentuated but at different scale- bulk of photon energy transfer.

      • logan says:

        On differing of some comments saying Solar flow shouldn’t be called wind, find it fitting. Ducky’s should be called also.

      • logan says:

        ERRATA: The shield is expending a lot more.

  • logan says:

    At a previous blog’s linking was commented of a very actively accreting young star apparently eating very massive objects.

    Now a new numerical advance brings a more plausible scenario: Multiple proto-stars creating an initial setup of highly turbulent circumstellar arms and arcs, clumping material at their vortices.

    The modeling is accompanied by new IR supporting observations.

    “The synergy between the presented observations and the hydrodynamics simulations with radiative transfer modeling indicates that the formation and evolution of some, if not all, protoplanetary systems can be more dynamic and chaotic than was previously thought”.

    Wait, they say that initial heterogeneity in distribution of primigenial material is enough to cause these instabilities, at single point star simulations!

    Found it open from home, today:


    • Gerald says:

      This possibly turbulent past of our solar system might also resolve the origin of the mysterious Sedna TNO (trans Neptune object) family.

      • logan says:

        Hi Gerald. Agree. Those instabilities not necessarily coplanar 🙂

        • logan says:

          Specially the least gravitationally attached ones.

        • logan says:

          Maybe that’s why Scientists visualize Oorth Cloud as a Greek letter Theta:

        • logan says:

          Oorth Cloud then has an inner, single physical surface, -dual lobe shaped-. As the 2 grains within a coffee cherry. No External surface. Could talk of fuzzy, blending, flowing external envelope of Inter-Stellar medium our Sun is able to keep gravitationally bounded in her voyage…

      • logan says:

        The recipe of the
        TransNeptunians seems to sing at the same tone.

    • logan says:

      Always had ‘issues’ with accretion non being slowed, and eventually stopped once ‘pebbles’ reach a certain size.

      [It’s my view that accretion is happening everywhere, inside the forming environment]

      Multi-scale modeling is finally cutting this Gordian Knot.

  • logan says:

    Another tasks…


    Please keep up on the effort of building a healthy universal educative ecosystem. From the kids on the ‘favelas’ to the sparkest minds at our World Best Research Centers.

    Love you all 🙂

  • Daniel says:

    Interessting articel, like it

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