CometWatch – 6 January

This four-image montage comprises images taken from a distance of 27.9 km from the centre of Comet 67P/Churyumov-Gerasimenko on 6 January. The image resolution at this distance is 2.3 m/pixel and the individual 1024 x 1024 frames measure about 2.4 km across.

Montage of four NAVCAM images taken of Comet 67P/Churyumov-Gerasimenko on 6 January 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Montage of four NAVCAM images taken of Comet 67P/Churyumov-Gerasimenko on 6 January 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Rotation and translation of the comet during the imaging sequence make it difficult to create an accurate mosaic, so if you attempt a mosaic always refer to the individual images before drawing conclusions about any strange structures or low intensity extended emission.

The scene provides a nice view across the larger lobe (foreground) and up onto the smaller comet lobe (upper frames), taking in a wide range of surface textures from smooth regions with scattered boulders to rougher and more complex terrains.

Ramp up the exposure to bring out more details of the cliffs leading up to the smaller lobe, and to capture some of the comet's activity.

The four individual frames are provided below:





  • originalJohn says:

    Emily, you seem now to be reproducing these images with a very dark and under exposed appearance. This has the effect of obscuring some of the detail on the surface of the nucleus but more importantly it makes the jet discharge from the surface almost invisible, although it is apparent that it is still there, radiating in all directions. I appreciate that it is very much a compromise and that over exposure would saturate some surface features on the nucleus. Would you however, on some occasions, as you have in the past, show two selective exposures so we can get a realistic view of the very significant development of the jets as well as changes on the surface of the nucleus.

  • originalJohn says:

    Having done my own exposure adjustment it is apparent that the jets, rather than emanating from particular points, are issuing from large areas of the surface.

  • Bill Harris says:

    Dust Jets on 6 January 2015

    Polar Dust Jets on 6 Jan 15 A-B Image montage. Faint detail enhanced, with highlight masking.

    Source: ESA/Rosetta/NAVCAM
    CC: BY-SA IGO 3.0


  • Dave says:

    Re dust jet picture.
    Nice work again thanks Bill,
    There looks to be some strata or light and dark shade perpendicular to the jets. Is it anything to do with your processing? It can be seen on high zoom particularly on the right but also low down on the left.

    If not it looks like the jets are pulsing off the comet, I can't work out the frequency because I don't know the speed of the jets, but is it possible that the jets are dancing to the comet song?

  • Bill Harris says:

    That "banding" is a processing artifact-- we're pulling a lot of info out of a moderate-data 8 bit image and stretching/enhancing the low brightness values leaves "gaps" in the enhanced range. It's inevitable, and I tend to tune it out 'cause I know what it really is. This is why you read that "16-bit and 32-bit" images are better.

  • Gonzalo says:

    It looks to me that the stratification is from processing! I see a lot of that in photoshop .

  • THOMAS says:

    From the NAVCAM images which have been published over the past two or three weeks, the comet's jetting activity seems to have died down to virtually nothing compared, for example, with the truly spectacular display we were treated to *over four months ago* in one of the rare OSIRIS wide-angle images we have been allowed to see:

    Jetting activity should surely, on the contrary, have been ramping up proportionally as the comet approaches the Sun.

    Is there really that much of a difference between the NAVCAM and the OSIRIS images of cometary activity? If that is indeed the case, I suggest that we wait for the OSIRIS images to be released at last for comparison before speculating any further on the subject of the comet's jetting activity.

    • Robin Sherman says:

      I agree with you Thomas that the "visible" activity has not increased as one might expect. Although visible in more areas now, it is not as "spectacular" as we have seen. The issue here is we only SEE the dust propelled from the surface by sublimation gases. As all the movable sized dust particles are removed, the visible activity will decrease. To maintain or increase the visible activity, an increase in gas pressure to remove larger dust particles is required, or the erosion/sublimation process must produce more dust particles of movable size.

    • Jonas says:

      @Thomas - The image you linked to is heavily over exposed. That is why the jets are so obvious. Look at the images Bill have enhanced, there is also a better comparison between november and now.

    • Harvey says:

      The link at the end is interesting re OSIRIS capabilities; a previous post on this went AWOL somehow.

      Unforntunately, with the very low albedo & very neutral 'grey' appearance, it seems rather unlikely that the hyperspectral capability of the narrow angle camera is going to tell us a great deal, unless the NIR & UV filters throw up something. It seems nature painted comets with black gunk, & it only takes (say) a micron of it to hide whats underneath. The famous tholins perhaps?

      The narrow-band filters on the wide angle camera of OSIRIS target very specific gas bands & should be pretty unambiguous; some are just 4 to 5nm wide. These should tell us a lot more about degassing & jets. In this respect yes, OSIRIS can do a lot more.

      It would be nice to see some OSIRIS data!

  • Herobrine says:

    I have a question I've been meaning to ask for a while.
    According to a previous blog post here:
    "All Rosetta science instrument data have a proprietary period of 6 months, after which they will be publicly available in our archives, and thus all NAVCAM data will also be available no later than that." ( )

    That information was repeated in a later blog post ( ).

    It's good to know that the raw data is being made publicly available 6 months after it is acquired. For the NAVCAMs, that's uncompressed (lossless) 1024x1024 image sensor data at 16 bits per sample (65536 shades of grey), quite a lot better than the lossy-compressed 8-bit jpeg images that get released here. For OSIRIS, I believe it's captured as a lossless 2048x2048 image with 16 bits per sample, but optionally compressed by one of several lossy compression encoding algorithms prior to transmission, or transmitted without lossy compression, if desired.

    My question is, how do we access the "archives" mentioned in that blog post, so we may retrieve the data that is being made "publicly available" "no later than" the end of the "proprietary period of 6 months"?
    I'm aware of some old Rosetta data available at the Planetary Science Archive ( ) but there hasn't been any NAVCAM or OSIRIS data added there in years. OSIRIS and NAVCAM had resumed returning image data since shortly after the spacecraft awoke from hibernation nearly a year ago. For example, this wide-angle OSIRIS colour composite, and narrow-angle OSIRIS image were acquired on 20 March 2014: , 9 months 25 days ago, meaning the raw image data has been in the public archive (the one mentioned in that blog post) for well over 3 months now, so I was wondering where do we go to access the archive mentioned in that blog post?

    For reference, and to recall how long many of us have been tuning in to the latest Rosetta news, this image was acquired on 14 July 2014 and the raw OSIRIS image data should be publicly available in that archive (wherever that is) this morning. 🙂

    • emily says:

      Hi Herobrine,
      It’s an excellent question and one I have also been interested to find the answer to 🙂 I understand it works like this: in general the release of science data that is on a six-month proprietary period is made six months after the end of the previous six month period. So if we consider the data collected during the spacecraft’s approach to the comet and up to e.g. landing in November, then we’d expect that data to only be released in May (this is just an example, I do not know exactly the dates the individual science teams are working to). Then, data collected between e.g. November and March would be released six months later, in September (again, just general examples to illustrate the process). So the releases are typically made of the entire six-months (or other defined period) worth of data in one go, every six months, rather than a daily 'drip-feed' that is always only six months 'behind' on any given date. While that refers more specifically to science data, about the release of NAVCAM raw images I will get back to you once I have a clearer picture of the dates being worked to by that team.
      I hope that helps to clarify the process in the meantime.

  • originalJohn says:

    Yep THOMAS you are right. The jet activity could die down completely in the region nearer to the Sun. It has happened with other comets. If it happened with this one the ice sublimation promoters would account for it by saying the local source of volatiles had been exhausted. And if it started again at the same place it would be gravitational tidal effects forming an invisible internal channel to a new source. The old invisibility factor, which has already been used with this comet for non existent ice and non existent porosity in what is clearly dense rock.

    The electric currents that are driving the jets are actually invisible, except at the glow near the surface where the current density is highest. We could do with some nice startling discharges to the ionosphere as they switch to arc mode, to confirm the highly charged state of the nucleus. It is ironic that the lost lander is sitting there impotent somewhere with a flat battery on the surface of a body that is humming with electricity.

    • Alembe says:

      @ originaljohn,

      Please help me out with something. You say “the lander is … on the surface of a body that is humming with electricity.” Going back a long way to my pre-college physics, I remember that charge separates and accumulates on points. Ergo, if there is a lot of electricity/charge on 67P, then one end of it should be positive and the other negative, with the greatest charge accumulation/density on the tips the sharpest features.

      If this were the case, then would we not expect to have recorded massive discharges between 67P and Philae as it approached and skipped across the surface and finally landed? Additionally, would we not also expect the greatest electro-machining and dust production from the sharpest points where the charge is greatest?

      What am I missing here?

      Thanks, Alembe.

      • originalJohn says:

        A note of sarcasm from you Alembe. I think your physics memory has not let you down. I am of course, as you know, speculating based on the highly plausible electric theory of comets, because there are as yet no measurements of the electrical properties of this comet. Perhaps I should have said "wouldn't it be ironic if.........flat battery.....impotent.......turned out to be humming with electricity".

        As far as what happened when the lander touched the surface, nobody knows, except that it bounced off to an estimated height of 1 kilometre. Whether or not there was any discharge would have depended on the relative charge states of the lander and the nucleus.

        Indeed the greatest removal of rock and dust production would be expected at points of greatest charge concentration, but factors other than physical profile might also influence this, such as the overall charge distribution in the nucleus. I noticed a recent comment from one of the ESA staff saying about the jet emission that they had observed that, whereas it was initially confined to the neck region when first photographed, it is now spread more uniformly over the whole surface.

  • Harvey says:

    Rosetta will shortly fly out to about 140km (from memory) prior to the close flyby in early February.
    Firstly can anyone point me to the geometry of that manouevre relative to the sun?
    I'm wondering if there is any chance it will cross the bow shock. The RPG results would be very interesting if so.

    Comet plasma physics gets complicated (try some of the equations in the references 🙂 ) & Im not totally confident I understand the current situation.

    Papers like those cited at the end give estimates of the bow shock position around perhelion as a few thousand km out on the sunward side, anywhere say 1000-5000km. They also suggest that the bow shock distance is roughly linearly dependent of the gas production rate; it's intuitively obvious it depends on it, but not that its ~ linear, to me at least! The ionisation rate will also be lower at current distance. So with the currently much lower gas production & lower ionisation rate, well before perihelion, the bow shock should be considerably closer in - assuming the mass flow is high enough to form a bow shock, but I *think* the RPG data says we are inside it? - and could presumably be used to predict its position now - beyond me certainly. MIRO provided a gas flow estimate a bit back, but I cant re-find it; that could be compared to the values used in the papers to get a current guestimate.

    So, explicitly:
    - what is the geometry of the 140km fly out relative to the sun?
    - am I correct that there is a bow shock now, & we are currently inside it?
    - can anyone point me to the MIRO outflow estimates?
    - any chance Rosetta will cross the putative bow shock on the 140km fly out?
    - other, *closely related, real physics* questions!?

    Please note that I only intend to continue the conversation personally where it is a serious discussion of the subject of this post; the current existence & position of the bow shock & whether Rosetta might cross it.

    Rubin M et al.
    Plasma environment of a weak comet - Predictions for Comet 67P/Churyumov-Gerasimenko from multifluid-MHD and Hybrid model
    Icarus Volume 242, 1 November 2014, Pages 38–49
    DI 10.1016/j.icarus.2014.07.021

    Koenders C et al
    Revisiting cometary bow shock positions
    Planetary andSpaceScience 87(2013)85–95
    DI 10.1016/j.pss.2013.08.009

    And references therein.

    • THOMAS says:

      Hi Harvey,

      I have no intention of engaging you in a “conversation” which you will presumably refuse in any case judging by the terms of your comment.

      I simply wish to point out that what you call the “bow-shock” within the framework of the standard theory is, in plasma physics, the most visibly energetic part of a *plasma sheath* aka a *double layer* which forms the boundary of the coma. As you know, this is no “crank” or “Crazy Town” idea since the phenomenon of double layers, including in space, is well attested, most notably by the work of two Nobel Prize winners, Irving Langmuir (1932) and Hannes Alfven (1970).

      BTW, you probably also know that in its recent November 27 issue, the impeccably peer-reviewed journal Nature published a paper describing what is no doubt the latest, albeit less spectacular (since it has only just been detected…), example of this sort of double layer which just happens to be surrounding our own planet. I only have online access to the University of Colorado Boulder’s press-release. It contains the following quotation from the study’s lead author (with all the usual declarations of incomprehension and perplexity):
      “It’s almost like theses electrons are running into a glass wall in space,” said Baker, the study’s lead author. “Somewhat like the shields created by force fields on Star Trek that were used to repel alien weapons, we are seeing an invisible shield blocking these electrons. It’s an extremely puzzling phenomenon.”

      For the full press-release:

      • Prof Harvey Rutt says:

        To avoid confusion for others, double layers and bow shocks are completely unrelated phenomena. Wiki will explain.

        • originalJohn says:

          Unless of course Harvey double layers are mistakenly identified as "bow shocks". Then they are related. Note the recent affirmation by NASA that the confidently expected bow shock at the boundary of the heliosphere does not exist.

          • Prof Harvey Rutt says:

            Whether the heliosphere has a bow shock has no relevance whatever to whether 67P has a bow shock. They have been directly observed at several comets. The structure of a bow shock and that of a double layer are UTTERLY different, as is their physical basis. To suggest one could be mis-identified as the other is frankly ludicrous.

          • logan says:

            As I understand, NASA is saying: Sun is so placidly low speed to their inmediate galaxy enviroment, their 'shock' can't be 'bowy'.

          • logan says:

            I like to think of our Sun 'bow' shock more like a 'meduse' shock.

        • THOMAS says:

          @Prof Harvey Rutt (and "others")

          To avoid confusion for "others", Wiki by definition always explains the *consensus* position, whatever the article, the area or the branch of science concerned. As we all know, nothing more nor less can be expected from it. It is simply doing its job. And scientific breakthroughs, by definition, have never been achieved by consensus.

          The plasma sheaths aka double layers which are currently being demonstrated and investigated around both comet 67P and the Earth are part of *cutting-edge exploration* and are thus naturally not yet reported and even less explained by Wiki. The required updates to the relevant Wiki articles will take many more months, if not years.

          • Harvey says:

            Wiki simply defines what a bow shock & a double layer *are*.

            The signatures of the two are completely & utterly different as are their physical origins. That signature has been observed, in the expected environment, repeatedly.

            Double layers exist in terrestial & astrophysical plasmas, nobody argues about that. This relates to *bow shocks* only; which also unambiguously exist. (Its not impossible double layers might even exist in the region of a bow shock when the fine detail is understood; but they are not *required* there or intrinsically linked to it.)

            The ludicrous EU tendency to distort any & every observation into an EU 'mould' is one of the aspects which justifyably leads it into disrepute.

          • Gerald says:

            This kind of "cutting edge" exploration turns out to be spurious ("fringe" or "opinion based") in most cases. So it's better to wait for some review and consensus, before adding it to Wikipedia, only to remove it again a few days later.
            There are other examples, where actual cutting edge discoveries are added to Wikipedia within hours.

          • originalJohn says:

            Well said THOMAS. And those who don't understand plasma miss the significance of the reproducibility of its effects over vast scales . So it is predictable that they would not see the connection between a comet coma in the solar current and the heliosphere in the interstellar medium.

          • THOMAS says:

            @ Gerald

            "There are other examples, where actual cutting edge discoveries are added to Wikipedia within hours."

            No doubt, but most often when the Wikpedia author is himself the cutting-edge discoverer....

            It always takes a lot longer for to get any change to Wikimedia articles on standard astrophysics, for the converse reason.

          • originalJohn says:

            No distortion Harvey, just application of plausible theory to observation. It can't be helped if it provides simple answers. Not ludicrous at all. Unlike the truly ludicrous ad hoc explanations and theories proffered by the mainstream for many things.

            The double layer is by the way plasma physics, not EU theory. Perhaps you would enlighten us with your own explanation of what a double layer is, and not wikipedia word for word.

    • originalJohn says:

      No discussion from me then Harvey, other than to point out that "bow shock" is a gas related misnomer. The coma is a plasma sheath moving within a plasma current sheet. Ions with enough energy will cross the boundary of the sheath and may be accelerated within it.

      • Gerald says:

        Shouldn't there be collisions of solar wind particles with more or less electrically neutral gas and dust from the comet's nucleus?
        Hence properly named.
        Those collisions will then ionize the formerly neutral gas to form a plasma.
        That's at least my straightforward understanding.
        Would be great, when Rosetta instruments will pin this down in more detail.

    • Gerald says:

      If the probe is inside the bow shock, or near the boundary, shouldn't Rosetta be able to measure bremsstrahlung or kind of synchrotron radiation?
      I guess it will take some time to analyse the data, but I'm confident they'll eventually publish according papers.

  • emily says:

    Hi Harvey,
    A very quick reply:
    -About the geometry of the Feb flybys – we are planning for a post about that in a couple of week's time so stay tuned
    -About the bow shock, I'll check up on that...
    -About MIRO, unless there was a talk at AGU (link via, the last post on here about that is here: (the table of parameters from this post may also be a useful reference:
    Hope that helps for now, sorry I can't provide more details right away!

    • Prof Harvey Rutt says:

      Emily, very many thanks. I'll find the out gassing rate and feed it back into the bow shock distance estimates, but a more knowledgeable response on this would be great.
      Is there any chance you could ask the flight dynamics group a question?
      Can significant information about the internal density distribution be deduced from precision orbit data? Not so much results, I doubt we'll get those this way 🙂 just is this something they expect to be able to do? It would be extremely useful if they can.
      And again, many thanks for your efforts.

      • Gerald says:

        I thought, they've been trying to work on the gravitational field in preparation of the Philae landing. But the gravity data are a little blurry due to the uncertainties about the drag from outgassing-
        I'd guess the Philae telemetry during descent, resp. the first td point, should give some more data points.
        Near the end of mission cometary activity will be low again. Very low Rosetta orbits have been considered for that late phase. If it will come true, this should be the best chance to get detailed gravity data, hence to infere internal mass distribution..

    • Daniel says:

      If you are doing a post about the flyby then how about some insight into the planning for the flybys as well. How instruments are prioritized, what they target for closest approach (imagining of specific features? dust capture to see if the lobes are different?) etc. Especially with the elusive Philae still lurking, hidden and silent, somewhere in the shadows, which adds another thing to consider.

  • logan says:

    On Earth we have solar wind down to about 100 km from surface, as auroras. On thinking of the micro? bars at 67P surface, I guess that most of solar wind should be hitting it. [Alter has a very 'unatmospheric' chat about this somewhere around here].

    If this guess ends being truth then, in a direct sense, 67P's sunny surface itself, is the 'tip' of the 'bow', as the nose of a hypersonic plane. Then, strictly speaking, Rosetta is crossing the 'bow' at most orbits, even the closest ones.


    You seem to be asking facts to the Teams, Harvey.

    • Prof Harvey Rutt says:

      Logan, the earth has a strong bow shock, but things are complicated by the presence of a strong magnetic field, absent at the comet. Wiki, bow shock, or earth's magnetosphere, has good explanations. The aurora does indeed originate in the solar wind, but not by direct 'illumination' by it. See wiki.

      • originalJohn says:

        Keep an open mind Logan, as you have now. Don't be over impressed by the contents of "wiki".

  • logan says:

    Thanks for the guide, Prof Harvey. According to the W definition then any magnet traveling trough a ionic medium can create their own 'bow shock'. [If traveling fast enough the magnet could create their own ionic medium! 🙂 ]

    • logan says:

      It has to be irrupting into the medium at supersonic speed to be called 'bow'. Amuse me this word in space matters 🙂

  • logan says:

    Just a memo to myself. Will allow me to keep focused:

    The composition of the solar wind is a mixture of materials found in the solar plasma, composed of ionized hydrogen (electrons and protons) with an 8% component of helium (alpha particles) and trace amounts of heavy ions and atomic nuclei: C, N, O, Ne, Mg, Si, S, and Fe ripped apart by heating of the Sun's outer atmosphere, that is, the corona (Feldman et al., 1998).

    SOHO also identified traces of some elements for the first time such as P, Ti, Cr and Ni and an assortment of solar wind isotopes identified for the first time: Fe 54 and 56; Ni 58,60,62 (Galvin, 1996).

    Note that although the solar wind is electrically balanced, the solar wind consists almost exclusively of charged particles (stripped away nuclei from atoms) and is an excellent electrical conductor. These electrically conducting particles is technically known as a plasma, so it may be misleading to think of the solar wind as like Earth "winds".

  • logan says:

    "Although the solar wind is electrically balanced", physical, chemical and structural heterogeneities can bring conductances, capacitances and impedances to 67P highly porous surface, Making of it a very active electro-chemical 'lab'.

    • logan says:

      I want to add a definitve word to this: eventually.

      Eventually any small surface of 67P will receive an equilibrated amount of charges...

      • logan says:

        At the micro level, electric balance is eventual. electric un-balance is the norm.

      • logan says:

        Magnetism at the surface:

        Would partially separate [by deflection] incoming protons, electrons and ions, bringing electric unbalance at the macro level, too.

        • Harvey says:

          Logan, as you are clearly trying to understand this, again a few brief pointers.
          We are now, at 67P, I think already *behind* the bow shock, which means not directly exposed to the solar wind. The bow shock deflects much (not all) of it.
          Its a 'bow shock' because its detached from the body (67P & environs) causing it; yes, its the transition to subsonic flow; it can be thought of a separating, crudely, 'comet space' from 'interplanetary space'.
          Yes, 'wind' is a bad term; look up the 'Parker spiral'.
          You also need to take into account the fact that the magnetic field at 67P is tiny (order nT) compared to earth order tens of uT, some 10,000 times stronger.)
          Weak fields take huge distances to significantly deflect the fairly high energy, heavy protons.
          The other ions exist, easy to detect, but in the bigger scheme of things are probably not that important, electrons & protons dominate that.
          At solar wind energies, further out before there is heavy degassing, the proton sputter yield is very low. The protons are mainly just 'buried'.

          • logan says:

            Thanks a lot for taking the time, Harvey.

            Being protons so heavy and 67P magnetosphere so weak as for them to be significantly deflected. I am accepting your argument, on a theoretic level.

            But, what about electrons? Personally do not expect them to arrive at so low 400km/s average speed. I expect them to be a lot more energetic. If not, they would be so light as to be significantly deflected, even by weak fields. Also preferentially absorbed (to protons) into 67P gassy emission. Solar storms inducting electric havocs on space equipment (as an allegory) make me wonder if solar electrons could travel faster than solar protons.

            'The protons are mainly just 'buried'. Yea! I visualize them as 'just going under' 🙂

  • originalJohn says:

    You would do well, Logan, to ignore the bow shock fantasy. The truth is that the coma of a comet is a plasma sheath within the different plasma of the heliosphere. The boundary between two plasma regions with different characteristics is called a double layer. It is a self forming boundary and has its own special properties, There is no deflection of the solar wind (solar electric current) protons at the boundary. They have very high energy and pass straight through it. The positively charged protons are then accelerated towards the negatively charged nucleus and the proton stream is greatly increased in density by the action of its own self induced magnetic field before it impacts the rock surface. The boundary of the comet sheath would more accurately be thought of as a bow suck.

    By the way, the Earth's magnetic field deflects the solar wind current in the equatorial region but it provides no protection at the poles, where the auroras form. So when there is a coronal mass ejection and the solar wind increases in intensity the auroras become much brighter, because they are carrying much more current.

    Even if this comet had a significant magnetic field its overall effect would depend on the orientation of that dipolar field to the direction of solar current flow.

    • Gerald says:

      I thought, it should be clear by now, that the comet can't be electrically charged to a degree, that it can significantly alter the motion of solar protons by electric fields.

  • logan says:

    Hi OriginalJohn. 150 to 200 Km above the Earth's Poles? I am admitting Auroras as a manifestation of plasma sheath phenomena.

    Nowadays, also admitting that, at Earth's equator strong magnetism should be the main agent causing a 'supersonic', 'bow shaped', 'shock wave' deflection of most of the constituents of the solar wind.

    Also, at 67P -if and only if- supersonic to subsonic deceleration of solar wind is occurring, then admitting from Harvey that it should be mainly caused by Ducky's weak magnetosphere.

    Persisting as a mule that most of the solar wind particles should be trespassing this proposed -and also weak- 'bow'.

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