CometWatch 20 November – In the shadow of the coma

This NAVCAM mosaic comprises four individual images taken on 20 November from a distance of 30.8 km from the centre of Comet 67P/C-G. The image resolution is 2.6 m/pixel, so each original 1024 x 1024 pixel frame measured about 2.7 km across. The mosaic has been slightly rescaled, rotated, and cropped, and measures roughly 4.2 x 5.0 km.


Four image NAVCAM mosaic comprising images taken on 20 November. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Due to rotation and translation of the comet during the image taking sequence, making a mosaic involves some compromises, as features change slightly from one image to the next. In addition, scattering in the NAVCAM optics can lead to large-scale intensity artefacts which are difficult to cater for when mosaicing.

Thus, for this set of NAVCAM images, some pre-mosaicing masking and post-mosaicing localised intensity adjustments have been made to reduce the low-level artefacts. By their very nature, these adjustments are not perfect. However, as always, the individual images have also been made available below to allow you to check the accuracy of the mosaicing and intensity matching.

The image shows vast outflows of gas and dust, as well as smaller ‘jets’ stemming from the neck and the larger lobe of the comet, suggesting increased levels of activity since rendezvous in August.

Post-processing in LightRoom was also used to bring out the faint outflows, while retaining the brighter features on the comet. Exceptionally, an increased exposure and contrast version of the mosaic is also provided to give an even better view of the outflowing material.


Same as the mosaic above, with increased exposure and contrast. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

In particular, at the bottom of the mosaic, the non-illuminated part of the comet stands out as a silhouette against the broader diffuse emission coming from the comet's coma. There are hints of a diffuse 'atmosphere' close to the surface of the comet seen along the illuminated edges, but this could be due to scattering in the NAVCAM optics. The large number of small white blobs in the image are likely specks of dust or other small objects in the vicinity of the comet.

ROS_CAM1_20141120A ROS_CAM1_20141120B ROS_CAM1_20141120C ROS_CAM1_20141120D



  • Redgy Devos says:

    Outstanding pictures from the navcams. Can't wait to see the dustjets as seen by the Osiris camera!

  • Ingo Althöfer says:

    What a nice post-processed picture!
    Thanks a lot for showing.

  • Harish Mehta says:

    I developed hobby of sky gazing and to track latest astronomical events happening . Seeing comet photographs make me miss my heart beat and got goose bump. I have photographs of Helly's comet

  • Jacob nielsen says:

    That brim top, left: snowdrift. (coherent dust of some sort, deposited as a function of ejection / reimpacting on a rotating body). Haven't noticed that feature before; previously unphotographed?

  • Robin Sherman says:

    Excellently done Claudia, a wonderful image. It can be compared to the image taken on 19th September, which is taken from almost the same angle and distance.

    The greyness of the coma in the background is now very noticeable, highlighted by the silhouette of the comet. There is loads of debris floating about, some of which is pretty large. At about 995 x 1020 there is a large white blob. It appears to be in the path of a jet, or being propelled by it, as the jet splits either side of it. This would mean it is at the same distance as the comet from Rosetta. I reckon its about 4 pixels across so that makes it in region of 10 metres across, there is even a hint of a shadow on its underside. That is one mighty big snowflake/dust ball. The gas we can't see in the jets must be exerting a considerable pressure.

    The light reflected from the coma is now strong enough to illuminate the shadows from the sun sufficiently to show quite a lot of detail of cliffs and crevices. It is noticeable the near side of the big lobe, which we have not seen so much of before, is extremely rugged and looks more like the surface of a glacier, with deep ravines and crevasses.

    The patch of dust dunes can still be seen, though not as well defined from this distance and the large crack running along the base of the neck. I still can't see any obvious significant activity from it though. The large lobe seems to be more active than the small one, is this due to less dust, fewer volatiles left near the surface or less illumination?

    Finally Bob the Builder has returned. At 435 x 1400, if you zoom in a couple of times, you can see him lying down peering into a pit, presumably still looking for his saucepan.

    • Bruce says:

      Thanks Robin,

      I also noticed the large crack along the base of the neck, which is more obvious in the 19 Sept image.Does it potentially extend through the whole comet and represent a fracture zone.

      And the distinct shaddowing on the large white blob (995 x 1020), does suggest that many of the "small white blobs in the image" are more than just "specks of dust or other small objects in the vicinity of the comet." It makes sense that if a comet is a frozen rubble pile, that some of the rubble will break free - perhaps completely - as it thaws. Much will remain gravitationally bound and reassemble as the comet retunrs to the freezer. I wonder if the Osiris camera is being used to image any of these larger free-range blobs.

      I don't quite get your Bob-the-Builder reference. Are you referring to the pair of legs about 10 pixels long?

      • Robin Sherman says:

        This is a long running theme in the Blog going back a few months about Bob the Builder, who even posted himself to confirm he was there on 67P. Hence any feature that looks like a human figure to me is assumed to be him.

    • No news says:

      Hi RS, the size of the fluffy flakes can not be estimated by the size or amount of the pixels covered due to its huge, almost 100% albedo and the camera used plus the image editing present.
      On a prior NASA mission to a similar comet the flakes where estimated to have a maximum size of 1/3 meter in diameter.
      Apparently no one at ESA is able to make any comments about the science facts about such things like coma, streamers or floating shapes. Its sad facts.

      • Robin Sherman says:

        I totally accept your reservations Nn, and my estimate was little more than a guess, but it does appear there are some large metres size bits of debris floating around 67P. With such a low gravity and density of materials, ejecta of that size should not be unexpected that close to the comet's surface. The NASA evidence you mention was for bits of coma a lot further from the nucleus, but does illustrate we are not talking just grains of dust making up the coma.

  • logan says:

    What a vessel!

  • logan says:

    Permission to go on-board 😉

  • Bill says:

    Whoa. You have done an exceptional job today.

    I am speechless.and have nothing to add...


  • JP says:

    Great view, great picture, excellent editing...
    now the coma is finally bright enough such as to see the outline of the night-side of the nucleus. As far as I can tell, the only back-illuminated features are illuminated by the nucleus, not by the coma.

  • Robin Sherman says:

    I posted this on Monday's blog, but this new fantastic image appeared as I was doing so, so I'll post it again. Its from our friend Matthias, he has been playing with his toys again to generate this brilliant image from the CIVAS landing panorama.

    Now compare the boulders and their positions to the view from the circle in these images, where I think Philae is hiding.

    • logan says:

      Thanks a lot Robin and Mattias. Makes a lot easier the perception 🙂

    • Robin Sherman says:

      While passing a cold damp November afternoon I thought I would add some fancy annotations to these images, as others have done. I have added the wider view of the comet for some context.

      The trajectories are in no sense accurate or to scale just illustrations, but the first bounce trajectory does show how Philae could be seen in flight in the OSIRIS images next to the bright boulder. Also I tried to show how Philae has slightly drifted in direction due to the rotation of the comet beneath her.

      The next two images have been annotated to circle the same "cryorocks" and features in both images. The key point to look at is the area of the white square. There is an indentation in the "cryorock" seen in both images and crucially the blue circled boulder can be seen through the gap. This is a very particular view that is likely to be unique.

      Altogether with the lighting, telemetry, and CONSERT data, I think this is a convincing case, but no doubt as usual will be proved otherwise once the OSIRIS views from 20Km are available. We have to assume that those from 30Km were unable to pick out Philae or else we would have heard by now.

      • logan says:

        Hi Robin. We have to look for a new, nearer, low altitutide impact.

        Impressive your graphic 🙂

    • THOMAS says:

      Mattias Malmer's image is indeed extraordinary, with all that in-depth perspective showing us precisely what sort of incredible jumble of rocks and boulders Philae finally came to rest in. Better than 3D! From the shadow, you can actually sense the cliff-face sloping upwards to the right....

      • THOMAS says:

        I just hope that no more rocks fall down from the right off that cliff-face in the coming days/weeks/months on top of Philae.

        Personally, if I were up there, I'd avoid the area but apparently Philae is stuck there till the end of time....

        For those who haven't seen it yet, here's Mattias Malmer's reprocessed image again:

        Many thanks to Mattias for his extraordinary perception and to Robin for bringing it to a wider audience on this blog.

  • Raymond says:

    Beautiful pictures. Btw am I The only one who sees a status of Easter Island in this picture. 🙂

  • ogan says:

    Just look at the mosaic with increased exposure and contrast, and bend your neck to the right... 🙂

    • logan says:

      The speed of those jets are high compared to rotational speed. They are parallelized along the back border of the body.

    • logan says:

      The collimations are such high speed they look linear.

  • gg says:

    Jar-Jar? :-O

  • Ross says:

    I can't WAIT to finally see a picture of a vent which is supposed to produce these spectacular jets.

    • originalJohn says:

      Well Ross, as you know, you will be waiting a long time, about as long as I will be waiting for an analysis of the jets showing they are neutral gas.

  • Nick in Wales says:

    I will be interesting to see if emissions just grow steadily or they increase in distinct bursts or steps as our icy friend hurtles towards it's perihelion. Are there critical temperatures or other conditions which when reached cause a sudden increase in coma activity? Just pondering like. 🙂

  • Sovereign Slave says:

    Wow! Simply amazing.

  • algol says:

    Is there some kind of primitive atmosphere of sublimated material on some Sun-exposed surface fragments? it's seen in the increased exposure pics, in the vicinity of edges. or it's rather some kind of CCD bloom/optics effects?

    • logan says:

      Hi Algol. Ions travels relatively fast. Should be mainly dust. Static electricity could be playing a little around there.

    • logan says:

      I ignore CCD details. Don't know if photon and electron isolation in sensors of that age 🙂

      • algol says:

        Thx for reply. well, as other users said already - maybe it's really just an effect of scattering of light in ejected comet material between comet and rosetta which make edges to glow?

        • algol says:

          well, in the main text, there is hints of that effect already;). I didn't wrote it all;):

          "In addition, scattering in the NAVCAM optics can lead to large-scale intensity artefacts which are difficult to cater for when mosaicing."

          "There are hints of a diffuse 'atmosphere' close to the surface of the comet seen along the illuminated edges, but this could be due to scattering in the NAVCAM optics."

  • Atom Universe says:

    what are those tiny white particles, Is it ice?

    • logan says:

      Hi Atom Unverse. No official comment yet. Believed here it's fluffy snow.

  • Max says:

    The processed photo has a dramatic style somehow very reminiscent of black-and-whit film photography. It really stands out among all the other images.

    With the scattered light from the developing coma, I wonder if we'll soon have anough backscatter to see features in the shadow. On the other hand, at some point this will certainly act as a kind of diffuser or soft-focus for the surface images in future, rather like Earth's atmosphere does.

    Taking this one step further, I wonder if we'll reach a point where a significant amount of light will be backscattered towards Philae's soler panels even while it's not directly illuminated?

    • Robin Sherman says:

      Hi Max a couple of good points there. I think the "clarity" of the September 19th image compared to this one illustrates the problem of "soft-focus". Zoom in on both images in the same area and the loss of sharpness and detail is clearly visible.

      The extra illumination from the coma may help Philae in the future, but the balance to that is the direct sunlight is also scattered by the coma and its intensity reduced. Remember what appears as a bright sunlit surface is reflecting only about 5% of the light from the Sun. The amount of light coming from the barely visible coma, is still small even compared to reflected surface light. The only advantage to Philae is that it comes from all directions.

    • JP says:

      Hi Max,
      I previously estimated the brightness from the coma, using a number of assumptions (principally that the coma is not optically thick). I estimated the coma brightness to about a faint moonlight at maximum. So even if efficient in low-light, Philae solar panels would simply not produce any noticeable power from that.
      I used past observations of the comet coma, their associated brightness and extension to make this estimation. But no one had reviewed this estimation, so feel free doing so...

      • Max says:

        Hi JP, Robin,

        I'm glad someone considered this, and wouldn't dream of putting your results into question; anyway I have far too little hard information from that, and anyway both your comments seem perfectly logical to me. So we'll probably have to continue fiddling our thumbs for Philly till next summer.

        Anyway, if even an interested layman like me can learn so much new about comets from this mission, I can't begin to fathom what our scientific friends will find out. And we've already learned so much that could be applicable to the next mission that'd rendezvous with our land on a minor body. It's really something to be excited about.

      • logan says:

        Hi JP. Do you have a link to your estimation? Thanks 🙂

        • JP says:

          Hi Logan,
          Sorry, the captcha were broken yesterday, ESA might have forgotten paying the google tax...
          I can't find the post, so here is the quick calculation, it is based on the conservation of étendue.
          67/P is typically of magnitude up to 9 at its brightest, for a coma approximately 1 arcmin in diameter.
          Bringing back such an object that close that it occupies the whole sky provides a total brigthness about 150 million times larger.
          This corresponds in turn to an object about 20 magnitudes brighter, i.e. magnitude -11, which is about the luminosity produced by a faint Moonlight.
          There are large assumptions in my calculations, but I am confident they do not change the conclusion: Philae will not benefit from coma-scattered illumination. If we are to wonder about alternative contributions, illumination by neighbouring rocks will be much higher, even if they are as black as coal.

  • Dave says:

    great pictures

    If it is sublimation though, what is powering the acceleration of the dust and gas. Even our fasteest steam engine, Mallard, can't puff that hard.

    It looks like one or two of the jets are eminating from this side of the horizon, but there does not seem to be anything resembling nozzles to concentrate the flow in the areas under the jets.
    The picture promises to deliver but still holds on to it secrets.
    I have old eyes though, maybe someone else can decipher.

    Strange also how new views show things you have seen before in a different perspective.
    I particularly like the half pipe, exiting the large crater on the right. So difficult to ski it though, while its full of debri.

    • Ross says:

      There is nothing resembling nozzles anywhere on the comet. In fact, many of these jets seem to be sourced from the edges of terraces and peaks.

  • Sylvain says:

    CometWatch 26 (and not 20, which already exists...) I guess ?

    Anyway, awesome picture !
    Thank you for let us dreaming ESA !
    Her's my tribute to Rosetta & Philae

  • Jacob Nielsen says:

    When Rosetta approached 67p a pet name came to be: Rubber Duck. A name referring to shape, not size or composition. BUT it seem likely that crosslinking of organics (containing unsaturated C's) could occur over some lenghty time, especially when ejected in the coma. Sulphur could be Involved..? Hence rubber.

    • Marco says:

      Yes - I had mentioned somewhere previously that the black substance could be vulcanised rubber. Very ironic with regards to the duck shape and now Philae "bouncing"

      • Jacob Nielsen says:

        in the October 23th post sulphur was shown to be in the coma. Most likely the blackness of 67p is carbon black, but many different organics will rest on the nucleus, among them unsaturated ones. industrial crosslinking of rubber requires peroxides or sulphur - and high temperatures or long curing times. On 67p maybe cosmic radiation? I found an article that described the use of plastic as a means of shielding against tissue damage from cosmic radiation - a lot of interaction between the bonding energies in organic compounds and cosmic radiation. (That is why cosmic radiation damages our tissue in the first place). Some parts of the surface of 67p could be something resembling ebonite. Certainly it's not ebonite all the way through, and I will not begin to speculate on structure vs. density etc. And I don't think it will be "bouncy".., only way to be sure if it really is a rubber duck: if we squeeze it, it should make a sound 😉

      • logan says:

        You make me nervous Marco 🙂 Plasticity had I considered, not elasticity. do you know of any earthly rubbers at 180ºK?

      • logan says:

        OK, does high temperature silicones have Fe in their formulas? If inside a graphite matrix here your 'stealth' skin 🙂 [Just playing]

  • No news says:

    After so many images from the very start of the first orbits around the comet those streamaers are present and of a variable presence, sometime faint and sometime dense.

    Is it just me or is someone else wondering why ESA is not capable of give an estimate or at least an educated guess what is initiating thesse streamers.

    I know what i think and also know what a lot of others think but i would read what some researcher at ESA think. Are there any researchers at ESA that are occupied with the study of the coma and its origin at all? If yes why is it so hard to deliver an intermediate report in layman's term that do not compromise any polices or ruin some career?

    Honestly, ESA has clearly declared that its all about science fact. It is about time to live up to this declaration.

    • Dave says:

      Maybe like us they dont know enough yet.
      For the various sublimating ice models, there has to be ice somewhere, on the surface, under the surface or as part of the rock.
      The data so far released reports things like, - could be splintered ice or not inconsistant with a hard ice. There still appears to be no direct evidence of ice.
      For the eletrical universe model, there needs to be evidence of magnetic fields that can hold the 'jets' in columated streamers, plus measurement of plasma flows, some high temperatures on the ground.
      We have not seen very much detail of this, even though there are instruments designed to measure. Perhaps nothing is showing, or instruments giving are inconsistant results.
      For the people who believe there is water inside the hard core of the comet, then presumeably they wish to see what the internal structure is. All the models want need that information but there appears to be some problem because the position of Phillae is not accurately known. So any figures to clarify the structure have not been released. Maybe these results are ambiguous in some way.
      Then the density figure for the comet does not appear to match anybodies expectation what ever model they are using, so again we need some good view of the internal structure and some clue at least what the surface is made from.
      Also the surface temperature has always been considered hotter than the standard model would have suggested by some 30degrees or so. We have seen an average temperature map some time ago, but the comet is more active now so I assume things have changed. Also temperature wise it would be nice to know peak temperatures and where they are and lowest temperatures and where they are.
      Maybe the data for this is unambiguous.

      With so much data seemingly not available or in some way ambigious, if I was one of the senior scientists, reporting to the world, I would be very carefull what I said especially if I did not have complete confidence in the results or maybe not having corroborating facts from two or more diffent approaches.
      I dont think we should have even educated guessing from them, the media often seems to latch on to things, especially if it makes a good headline.

      • Prof Harvey Rutt says:

        The only significant point on which I would differ regards the 'expectation' on density. There are estimated densities for about half a dozen comets, and the average is around 0.6kg/L, going as low as 0.3, with substantial error bars. So the 67P value is not out of line (though how well that was know at the time of Rosetta's design I haven't researched.)

        It's perhaps worth pointing out *why* the instrument teams 'own the data'. People invest significant fractions of their working life in these instruments. There is often a huge gap between the effort of design, with minimal publication return, and years later, the results. To get people to comit to that, they need to be sure they will benefit career/reputation wise. So they get to mine the data and present it as they wish. That seems quite reasonable to me.

        • Dave says:

          Hi Harvey,

          I aree the density is in the range of other coments, but on this comet it was different to predicted (no error bars were ever mentioned for guidance)
          Also what ever the surface density is, because the comet surface appears to be solid and hard it begins to make the explanation of the the low density of the whole comet difficult to explain.
          Porous core or hollow core are ofcourse possibilities, but we are then back to speculating, untill we get some data.
          I am just a bit uneasy about the last paragraph, I think if you personally had sponcered the experiment and the building of the equipment, you may expect to be on a fast track to access the data.
          I appreciate that we have to give the scientists time to get it right and make sure the numbers work, but this is publicly funded research and so there is some responcibility that the scientists have, to reasonably communicate something (other than the 'not inconsistant with ice' type of statements).
          After all we have put the roof over their heads for the last 20 years.
          Early in my career I worked in cutting edge R&D for a large multi national, each sites R&D worked in isolation. 8 years into one major project, where we were world technology, it became apparent that two sites were working on the same issues. It was a shocking waste of research, and probably would of knocked 2 years off the project if we had been communicating with each other.
          I believe that some sharing is important its easy to think its your baby, when in reality there is a whole project team, not just the scientists but also, all those people who have contributed, they are part of the team that has made this incredible project a success.
          It looks like a sermon, not meant to be just an opinion, sorry.

        • No news says:

          Hi PHR,
          The people that invest some time of their life at work on parts of this mission are paid for their efforts and are not held as slaves. They do this for a living and mostly are paid by tax money. The result is not their property if they are not acting as private enterprises. If they are private investors then they also paid a lot to get on board these vessel, say 50 million € per kilogram payload. Who did that? I know the origin of some of the instruments and still see no result of those experiments that are performed with those instruments that are owned by me, you and other tax payers. The researchers only own their ingenuity and are allowed to make a career and will do so if it is some value in it, this is what drives them to do this well paid labor. Others will have their go as well once the treasure boxes opens and then it will be clear who are the most ingenious scientists and why this sad delay was just a waste of time.

          • Prof Harvey Rutt says:

            Basically, without an arrangement of this kind, you are not going to get University researchers to work on it. At the moment, much of it is done in Universities and Research institutes. They are paid far less than they would be in industry, and the work is effectively heavily subsidised., and a heck of a lot of unpaid effort goes in to it.
            Sure, you could do it fully commercially, but it would cost a lot more, and you'd probably end up paying the University guys as consultants.
            Be that as it may, right now the contracts are as they are, and those working on them clearly have a right to see the contract honoured.
            The other aspect here is that proper analysis of complex data takes time, whoever 'owns it' and controls its release. Some of this data really is complex to interpret, CONSERT in particular for example. Personally I would prefer a slightly slower release of considered and properly analysed results to a stream of 'whoops sorry...' Which would otherwise result.

        • logan says:

          Hi Prof Harvey. I understand the personal dilemma. The system, as is now, is wrong.
          Nowadays, I have even seen scientists who seat in their raw data for all of their life. Doing 'remakes' of just one investigative work. I have seen them 'dressing' his coffin with the raw data.
          Publicly paid investigative works should belong to the people who paid it. More than nothing the 'raw' data.
          No public investigative work should be approved without very clear, simple and 'pronto' terms for fully open delivery of all of the 'raw data' and methodology, in a FOSS format.

        • logan says:

          Hi Prof Harvey. "...Some of this data really is complex to interpret". Agree, specifically on CONCERT. But 'publicly supported' experiments shouldn't be designed that way. Essentially, that is an error in experiment design. Complexity can be 'modularized'. Bigger -true-, but more reliable and peer friendly [and public friendly].

    • Robin Sherman says:

      Part of the problem is the scientists and their instruments are not part of ESA. ESA can only pass on what the scientists tell them. ESA's involvement is principally the building, operation and flight control of Rossetta, hence we see a lot of NAVCAM images, because it is ESA's instrument.

      The project scientists of the individual instruments are free to release any information they are going to share through their choice of media it seems. Some have been kind enough to share some of their data with ESA, mainly only at ESA's big media events, even then ESA has to ask them for images etc.

      ESA has been clear to point out that this mission could only happen because the spacecraft instruments were paid for and built by outside consortia of research institutions and private industry. The instruments and their data belong to them, not ESA.

      Having said all that, ESA's own science team do seem to be very reluctant to come forward and give "intermediate reports in Layman's terms" as you say, but they are hampered by the same situation, they have little more access to the science results than we do.

    • JP says:

      Hi No news,
      well, I guess science has never been made in a blog, has it? The very first papers (actually more letter) have been published on Rosetta data, and they of course look desuet*, based on images a couple of months old... Science means reflexion, review and publishing delays.
      A blog means a totally different reaction time. Frustrating, but it leaves us a vast area of discussion without borders. What do you think about the origin of these streamers?


      • Robin Sherman says:

        Hi JP. There was some discussion here a while back about streamers/jets, their mechanism, origin and nature. Bill found an interesting paper showing computer models developed from previous comet flybys, which explained how collimated jets could be produced by subsurface sublimation passing through a porous, small grained surface layer. I likened it to how a liquid flowing through a filter is collimated into a central stream. The analogy of subsurface hot springs producing "boiling sand" in a lake in New Zealand added to that, gives me the impression that "vents" and "pits" may not be seen as the source of jets, but as the post activity evidence once the dust layer has been removed.

        Looking at where the jets are coming from on the bigger, body lobe, they would seem to be coming from the vast plains of dust we have seen on that part of the comet. The evidence from this image suggests that the remains of crater rims act to collimate larger areas of sublimation too. How the dust in jets becomes visible is also a factor in where they are seen to emanate from in these images. As others have pointed out earlier, only those with the correct angle of illumination will be visible, so there may be more streamers, but such is their diffuse nature they can't be seen in this NAVCAM image from this angle.

        Sublimation from exposed areas of "cryorock" seems to be in the form of a low level haze that slowly drifts away from the surface into the coma. Elizabeth and Marco's image I posted above, seems to show this particularly well. The earlier post from "algol" refers to this as well. Studying the images from NAVCAM when less than 10Km from the surface, gas plumes rising from exposed surfaces were visible as a sort of "heat haze", as there is very little dust to make them visible, just what is embedded within the "cryorock" itself and released on sublimation of the icy matrix. In fact such is the size of these plumes, as activity has increased, a few can still be seen from Rosetta's current 30Km orbit emanating from the bright, exposed surfaces of large "cryobolders".

        • Prof Harvey Rutt says:

          Do you have the reference to the jet model?
          Would be helpful, though I may be able to find it.

          Fluid dynamics is not exactly my strong point, and I'm very unclear what sort of conditions might exist. I'd been musing on how it would work with a heat flux limited ablation source and possibly a choked flow situation at the vent?

        • JP says:

          thanks for the somprehensive summary.
          On a different matter, considering the fact that the orbit exposes one hemiduck only once close to the Sun, while the othe ris exposed mostly far away from the Sun, one could expect that, orbit after orbit, the composition of both sides differ quite noticeably, as well as their shapes. For instance, one side with little dust because the sublimation rate is so high it blows away the dust...

  • robert nelson says:

    on 26 Nov Stubbe Hviid said;“The transmission takes place through a microwave signal which is comparable to a flashlight in energy”
    I was wondering if it was an incandescent or LED light source
    Thanks again for the GREAT pictures you have been providing

  • logan says:

    Estimating those jets in tens of tons per orbit, would not be surprised if the spin vector going up.

  • Two of our processing (handmade!):

    standard b/n:

    Colorized to highlight both, profile and jets:

  • Gilbert says:

    I hope Philea is found sooner rather than later because when I see these contrast enhanced images and imagine the specs to be more material and less optical artefacts I fear that in time Philea will become smothered and buried in a seething cauldron of rock and ice.
    Even if Philea doesn’t reawake just knowing her exact location has scientific value.

  • Kim says:

    Sorry about that Hello comment I actually meant, where is the probe now? Is it in the comet or still travelling?

    • Prof Harvey Rutt says:

      Philae is on 67P, but dormant.Rosetta in in orbit around 67P. There is an excellent 'where is Rosetta now' tool on the ESA web site.

  • Prof Harvey Rutt says:

    Im not sure we differ much. If they were still sitting on the data a year hence, I'd be yelling too. But ensuring those who invested in it get a first shot at it, and time to do a proper analysis before publishing, seems reasonable to me. So far we are talking a few weeks!

    Re the structure.
    It is indeed hard to envisage just how this thing is put together. Seems like a sort of solar walnut 🙂
    But I think much of that is our very earth bound view of processes that make 'things'. We are not used to what happens in a hard vacuum, periodically ablated, low Gravity, exposed to hard UV/solar wind environment. Our intuition of how things 'should be' what 'things should look like' is pretty useless.
    In the end the data decides; too soon to call it, but it still seems like some sort of dirty snowball with a crust; leaving out those who just refuse to believe the data we have so far and fundamental physics, what competing model is there?
    If in a commercial environment there was 8 years of non-deliberate duplication, some senior management needs firing! In a university, you would not survive anywhere near that long befit ore publication made it evident.

    • Marco says:

      Harvey, I will repeat a competing model. I do not precisely endorse all details, but it is consistent with both data and the laws of physics: The wet comet model:

      Possible facts that would lend it credence are evidence for liquid water, or microbial life.

    • Dave says:

      Hi Harvey,
      yes we are more or less in agreement,

      Also making solid conclusions, when we are not familiar with low gravity and hard vacuum is difficult so we do need to wait for some figures
      It also means that we cant confirm the stardard model or any of the other on the blog just by observation, however wild they may be.
      Also if the data shows the current model is wrong I hope you are not suggesting we stay with it (''what competing model is there'') just because there may be no current alternative.
      The surprises with the comet data that we already have, visual & measured, do begin to beg the question HOW?
      The state of the topography, even though we are not familiar with the environment beggars belief if the std model is used. How for example are large swathes of material ripped of the comet making parallel valleys, a glancing collision with something could do it if the comet was soft and fluffy, but esa says the surface is Hard!
      There are raised portions with flat tops, this looks difficult to model even if there were significant plate techtonics.
      We were expecting a sublimation model with a smoother profile, it is impossible for me at the moment to imagine how such a craggy surface has resulted from sublimation.
      Plus now we can see that apparently more neck is missing than we have seen before, so this will probably mean a higher density when it is recalcuated.
      Slowly but surely the std model is falling apart.
      We will eventually have a lot of explaining to do or a new model.

    • THOMAS says:

      @ Prof Harvey Rutt "Re the structure. It is indeed hard to envisage just how this thing is put together. Seems like a sort of solar walnut"

      Hi Prof,

      The evidence for a 'stratified rock' rather than a 'solar walnut' composition seems to be accumulating at all scales.

      I just posted this reply to Robin Sherman who asked for my opinion on his interpretation of a heretofore much neglected CIVA image of Philae's final resting place:

      I would, in my turn, be interested in hearing your opinion of our different readings of this image, which Robin posted with his annotations here:

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