CometWatch – 21 & 24 September

Today’s lead CometWatch image is a four-image NAVCAM mosaic taken on 24 September from a distance of 28.5 km from the centre of comet 67P/C-G (the four 1024 x 1024 pixel images making up the mosaic are provided at the end of this post). The images are background subtracted to remove some striping and fixed noise patterns.

Note that at these closer distances, it is harder to create accurate mosaics due to combined effect of the comet rotation between the first and last images taken in the sequence (about 10 degrees over 20 minutes), and the fact that the spacecraft has moved some 1-2 km in the same time. The mosaicking programme we are using (Microsoft ICE) seems to have done a nice job of stitching the images together, but if you refer to the four separate images you will see some differences in illumination and shadows due to this rotation and motion.

Four image mosaic of Comet 67P/C-G using images taken on 24 September. Credits: ESA/Rosetta/NAVCAM

Four image mosaic of Comet 67P/C-G using images taken on 24 September. Credits: ESA/Rosetta/NAVCAM (Click for higher resolution image)

Nevertheless, we can enjoy this very impressive view from NAVCAM, and can point out some interesting features. However, please remember that thorough scientific analyses of what 67P/C-G’s features are, how they came to be, and what they mean for this comet’s history and evolution will come in the form of scientific papers in the fullness of time.

Some obvious features that stand out are the large boulders, several metres across, lying in the smooth ‘neck’ region. Boulders are also seen at the base of exposed cliff faces, for example towards the top left in this image, and on the ‘head’ of the comet.

Other notable features include a variety of depressions with differing morphologies. One prominent example of a crater-like depression is located on the larger lobe (or the ‘body’), to the far left centre of the image. It is about 350 metres across with quite a well-defined rim from this viewing angle, and a mixture of ‘rubble’ and smooth terrain inside. Although the rubble is in shadow in the 23 September mosaic, it is clearly seen in other images, for example in the frame shown below, which was captured on 21 September.

Single frame (and slightly cropped) NAVCAM image taken on 21 September. Credits: ESA/Rosetta/NAVCAM

Single frame (and slightly cropped) NAVCAM image taken on 21 September. Note this image shows the backup landing site C. Credits: ESA/Rosetta/NAVCAM

In the same image (towards the left in the 21 September view) another family of depressions can be seen; these are characterised by both irregular and near-circular shapes, steep walls and smooth floors.

Another very different type of crater-like feature again can be seen to the upper right of the large depression in the main image (slightly to the lower right of it in the 21 September image), about 1.5 times the large feature’s diameter away. This one appears to be a rather fresh-looking small ‘dimple’, about 20 metres across.

As discussed during the EPSC conference earlier this month, the majority of the depressions on 67P/C-G have likely formed as a result of activity; that is, through surface collapse either as subsurface ice sublimates out through a porous crust, or as pockets of trapped gases are expelled.

But of course that doesn’t exclude impacts by external sources as a method of crater formation, although in general, due to the active nature of comet surfaces, impact craters that formed billions of years ago have likely long since been erased.

The origin of craters has been debated for other comet nuclei seen in brief flybys of other spacecraft. Fortunately, Rosetta is perfectly placed to determine the origin of these features on 67P/C-G, and if and how they may change over the course of the mission.


ESA_Rosetta_NAVCAM_140924_DESA_Rosetta_NAVCAM_140924_B ESA_Rosetta_NAVCAM_140924_C



  • Stu says:

    Absolutely gorgeous pics, thank you! :-)264

  • Peter Humphrey says:

    I'm surprised you don't draw attention to the feature that instantly caught my eye: the deep cleft between the neck and the head, which I hadn't seen before. It looks almost as though the head is being ripped off!
    Does the team have anything to say about this feature?

  • Mattias Malmer says:

    Image Cropping

    This cropped image:

    was originally rotated 180 degrees and had 154 more pixels of black "sky".

  • Bill says:

    What a wonderful new world to explore! Now that Rosetta is getting closer to the comet and has moved past the terminator line we are beginning to see interesting details.

    And thank you for the insightful comments on some of the features in these images. As well as presenting the images themselves!


  • Bill says:

    Nice! But what about more spectacular OSIRIS images? Yes, I know... proprietary data... 6 months delay to publish... Have to be patient, very patient...

    • Ross Dalrymple says:

      Whats this proprietary data business about! Isn't this funded by EU taxpayers? Its public property and these pictures should be released as soon as they come in.I cant see why not?

      • Denis says:

        Do you get results of publicly funded research against cancer as soon as the experiments are done?
        No you don't. Where's the difference ?

        • Martin Schäfer says:

          We do not want to get the results of the research! We only want to see a high resolution image of the surface taken by the OSIRIS system. The pictures of the NAVCAM are impressing, this is fact. But the difference between the image of Sept, 21, and Sept, 24 is insignificant. The resolution of the OSIRIS images must be gorgeous! Please let us see one of them!

          • Sovereign Slave says:

            I've posted as well about being frustrated with the lack of information, much less images, coming out of ESA. Found this very informative article about ESA policy/approach to information release:
            "Rubber Duckie Gate" indeed. So, like Rosetta has done in the past, and ESA has apparently done now with the public, I'm going to go into sleep mode and just check in every few months and hope there's actually something noteworthy they've deigned to release during the interim.

  • Kai Roesner says:

    Another fantastic image! Are there any plans to create a "cometographic" map of the comet's surface features? I imagine finding an appropriate projection method will not be easy, though...

  • Stuart says:

    apologies if this is an obvious sill question about the Rosetta’s lander Philae: the lander will fire barbs into the surface to hook onto comet 67P/C-G. However, as the gravity is so low, is there a chance this action will in fact propel the lander back into space (actions / reactions)?

    • Jason Rowberg says:

      Well, there's always a chance... but the ice screws tap into the comet first, actuated by the impact of Philae on the surface, so the rebound from that should be minimal. The harpoon fires simultaneously with a gas blast facing away from the comet (out the top of Philae) so again, the force away from 67P should be minimized.

      I guess we'll just have to keep our fingers crossed. You know ESA is planning for that contingency since the first round of picture data is being collected almost instantly after touchdown.

    • Dertutenix says:

      I think with a propellant of N2 H4+2 H2 O2 the resulting 4 H2 O+2 N will launch the harpoons into the soil without kicking the 100kg Philae. Back into space again. Its to be compared to fiering a pistol and not a canon.

  • Jacob Nielsen says:

    Absolutely! Therefore a thruster i fired simultaneously to force Philae down. Ther is a video that models this... Though in real lfe there is no smooth landing promise.

  • Robin Sherman says:

    Two more great pictures. No evidence for the crack, which caused much comment before, around this side of the neck and at the bottom of the neck area in this view there looks to be a solid less eroded lump bridging across the neck region. Should hold together for a while yet I think.

    Nice view of the backup landing site. I counted 6 boulders 10 to 15m in size and that big depression with a cliff at the end which must be around 50 meters high. A bit more level terrain but nowhere near as interesting as site J.

    To the right of site C it looks like a purpose built landing platform, (Star Wars Episode 2). Maybe it is an alien base after all. 😉 It would give amazing views across the neck to the smaller lobe. With the weird gravity vectors though it may be at some impossible angle as well as being just a "little" bit smaller than Philae's landing ellipse.

    Stuart A. Any plans to do your magic on these two pics? Really enjoyed the ones you did before on the 19th of Sep. picture.

  • Ross says:

    Emily, have electric discharges between the nucleus and its plasma environment been considered as a plausible explanation for the crater formation? Unlike the sub-surface ice sublimation, electric discharges can be falsified from above the comet and are direct results of cometary activity. If not, why not?

    • Rob says:

      @Ross - you already know why not - it's because the hollow faith-based Electric Universe "hypotheses" have regularly been roundly debunked by experts in the field as being pseudo-scientific nonsense.

      So, no - electric discharges/electric machining/electric golf-buggies, plasmoids and all the rest of the EU sci-babble won't be considered as anything remotely approaching "plausible explanation" for any of the features on the comet.

      But don't be disheartened - you can always get the IEEE or vixra to publish your "ideas".

      • Ross says:

        Debunked? Pseudo-science? Haha it sounds like you know nothing of the electric comet theory and are dismissing it without doing your dudiligence.

        The standard model consisting of water-ice sublimating is pseudoscience. It fits perfectly with Carl Sagan's description of pseudoscience,
        "Hypothesis are often framed precisely so they are invulnerable to any experiment that offers a prospect of disproof, so even in principle they cannot be invalidated."

        The coma was supposed to be formed by surface ice, but of course there is absolutely none to be found... so it must be under the surface where it can't be seen. The standard model is becoming unfalsifiable and that's not scientific.

    • THOMAS says:

      Ross, I fear that considering the mere possibility of electric discharge phenomena taking place on the comet is quite logically out of bounds for the mainstream astrophysicists who are leading this mission. "Electric discharges" don't need to be "falsified" if evidence of their existence is never disclosed. I'm just hoping that close-up OSIRIS pictures of those hot-spots on the neck where the discharges are clearly originating (but not only on the neck judging from other white-outs visible elsewhere on the nucleus) will provide the necessary, incontrovertible evidence.

    • Marco says:

      Certainly the crater shapes and features are not adequately explained by any known observed phenomena. How can electric discharges be "falsified"? Would electric discharges between the comet and plasma would be like "lightning", or like the migration of ions in a solution? I think electric comet theory will be falsified as soon as Philae lands.

      • Ross says:

        All scientific theories are supposed to be falsifiable. The electric comet theory can be falsified if substantial electric fields around the nucleus are not found. No electric fields = no electric discharges. Comas are "supposed" to be due to surface water-ice. No water ice exists on the surface and yet we have a coma, though the standard model is not falsified because they can hypothesize that the water ice is just under the surface where we can't see it. The standard model is becoming unfalsifiable and unscientific.

        • Rob says:

          @Ross, @Thomas - I hereby invite you both to submit applications to join the science team at ESA/Rosetta headquarters. Do come back here, both of you, and tell us how successful you were. Good luck with that.

          In the meantime, we can read about the progress of the Rosetta mission from real (= put in the hard work and effort to get there) scientists, talking about real science.


        • Marco says:

          @ross Saying that electric comet theory is falsifiable does not make it so. "Electric fields" are everywhere. No one is expecting zero electric fields. The same thing can be said of the electric field as of the surface ice. If it isn't found on the surface, there could be electric fields below the surface...... And so on. If there is a (minimum) particular measurement of electric field at a particular location at a particular time that would make electric comet theory viable or not, that would make the theory falsifiable. All I have seen from followers of the theory is vague references to what electric processes "can" do.

          • Ross says:

            Marco that makes no sense. If the jets we observe are due to electric discharges then the electric field must exist outside the comet nucleus between the double layers of separated charge, negative nearest to the surface and positive farther away. So, yes, the theory can be falsified if no electric field exists outside of the comet, or if the jets are sourced from an open vent in nucleus (never been found).
            That is clearly not the case with the water-ice excuse. If you can think of how to directly falsify the standard sublimation model with any conceivable observation please post it here (this shouldn't be difficult).

          • Marco says:

            @ross there are myriad other explanations other than electric fields and near surface direct sublimation for the emissions. It is clear to me that the emissions are neither, though I believe vents will be found when activity increases enough. Finding vents will not falsify or prove any theory. The vents are small and the velocity of emissions high. The reality could even be a combination of thermal effects creating gas pressure, and electric fields funnelling some emissions. The processes appear much more complex than a simple model can explain, and there is nothing pristine or pure about the elements and compounds found.

      • THOMAS says:

        No need for "lightning" on this small scale, just steady arc discharge (as in arc welding). That's what those so-called "jets" shooting up from the white spots on the neck (and other parts of the comet) are. Still waiting for close-ups of those white spots and the associated activity. They will confirm the electric comet theory. Perhaps not that surprising we haven’t been shown any yet. .

    • steve wiggins says:

      Regarding electric discharges: The star-like brilliance of Comet West (1976) in broad daylight was obviously due to some other type of energy than mere reflected sunlight. I'm wondering if anyone else ignored the negative media at the time and ventured out starting at 3 AM to witness this spectacular comet.

  • Ingo Althöfer says:

    Wow, what a scene. I know I should work -
    but I cannot help: I have to wathc first.

  • Mark Zambelli says:

    I know we have to wait for published papers on the morphology etc of the crater-like large depresions but they really look like 'inverted craters' ie the crater remnant equivalent of 'inverted channels' found on Earth and Mars. Shock-heated/fused material hangs around a lot longer than the eroding (or in the case of Churyumov-Gerasimenko, sublimating) terrain and causes the large circular depressions.

  • logan says:

    Amount of metallic elements vary wildly among the layers.

  • logan says:

    Well, there is a lot of deposits on the neck. Obviously they are not structural...

  • JohnM says:

    It is interesting to look at the boulders some on the sides of the 'neck' between the head and the body seem to be situated at imposssible angles and should have fallen 'down'. I presume they stay in place as the local gravity field at the surface is at some very strange angles due to the two masses. A map showing the calculated surface gravity would be very instructive.

    • Roberto Nesci says:

      A map of the gravity vector would surely be very useful also to plan the landing of Philae. And i think it has already been computed, but will be published later...

  • Xavier says:

    what you guys are doing is fabulous! every picture is a wonder and the participation on this blog is great; thanks emily for a very good curation!

    • logan says:

      That word is my very worst nightmare for all of what we have of space investigation.

  • Robin Sherman says:

    I have noticed that the latest pictures of the comet, in places it looks like melted chocolate poured over ice cream. That is, some thick slow moving liquid has flowed over the surface, then frozen, like a lava flow. This is particularly striking in the first image just to the right of the big black crater in the middle of the large lobe. So many of the depression/craters have large overhangs as "erosion" has undercut the upper layer of the surface, implying the upper layer is more compact or made of less volatile material. Eventually these overhangs seem to collapse leaving a cliff and scree slope of rubble and boulders.

    Could a colliding object transfer enough energy to melt significant amounts of ices, quickly enough for liquid to flow before it sublimates? Surely in a vacuum, unless the ices contain large amounts of contaminants, Nitrogen or noble gases perhaps, capable of lowering the triple point point to below 200K, water ice would instantly evaporate. I'm no expert on low temperature physics so I'm sure someone will tell me if and why my conjecture is complete rubbish.

    • logan says:

      Alright Robin, I didn't want to admit it. Those smooth, silly, putty surfaces over the craters indeed flow. Indeed are flowing...

    • Erich says:

      If comet scale objects, tons to mega tons of mass, collide even at slow speed a lot of energy is transfered into heat, also a very high pressure is created at the impact area.
      Any proper solids of frosen liquids will for sure melt and also evaporate. For some period of time the material will move around in form of gas liquids and solids. The thing is although that the gravity force is very weak and most of the movements will be in almost straight trajectories. Rivers running down hillsides is not really the case, the other way around like heated material in all form spraying up from underneath is most likely what will occur. The higher the speed of impact the more of the material will evaporate into space.

      • logan says:

        Remember those 'fluds' on polar regions?

        • logan says:

          But this mass is a lot more cohesive. Also think of ceramic 'mud' and long chain organics.

      • logan says:

        Low speed and fusion. This is new to me. This make possible a lot of phenomena. Even wobbling. Could anyone chat about the modeling of this, please? Need to chew a lot.

  • Bill says:

    Today's image is one of the better released pictures of the "North Polar Plain" which is the suspected source of the prominent collimated dust jet we have marvelled over.

    Here is a series of images from 8 Aug 14 to 24 Sept 14 showing the area over time and under different lighting conditions.

    source: ESA/Rosetta


  • Birgit Hofmann says:

    What for a wild and dramatic beauty.....wonderfull..
    And always : Go,Rosetta !

  • Stuart Atkinson says:

    Thanks Robin! New post going up on my blog soon.

  • logan says:

    Those 'mouths', 'vomiting' gas, dust and humidity.

  • logan says:

    Anyone using zoom see the 'scar' at 8 o'clock from the big shadow crater in the body? The scar is a 45ª line. The agent causing it is really heavy. (Consider how slow gravity is here).

      • logan says:

        Take the mosaic NAVCAM of Sept 24. trace an horizontal line just at the middle. Yo will be crossing a frontal big crater. Up and right of it. (By the way, the 'putty' dish of that crater has a big fracture).

    • Robin Sherman says:

      Hi Logan. The best view I could get showed a line of what looked like little pits surrounded by lighter material along the edge of a cliff jutting out into the sunlight. Could be active vents. About 10 of them all in a line. They could be a line of brighter little boulders and their shadows too.

      Another interesting spot is at the bottom edge of the "North Polar Plain". There is a very bright cliff which at the bottom has a clear demarcation from the plains material as if softer material has been "blown" away from the bottom of the cliff. The angle of the sun is almost perpendicular to this cliff face which would make it brighter, but it does seem to be a lot brighter than other areas exposed so directly. Its the first hint I've seen of what could be an exposed area of "ice".

      • logan says:

        Do you refer to the brightest pixelation just about the center of

        Don't have photo tools but they should be at top luminosity.

        • Robin Sherman says:

          No, thats just one of the landing lights for the alien base landing platform.;-)

          Could be an image artefact, but its a few pixels across so maybe a freshly fallen lump from the cliff edge with an exposed, "unweathered" surface.

          Oh for some close up pictures. Stuarts "Rubber Duckie-Gate" article gets more and more pertinent each day.

      • logan says:

        Have seen some 'dusted off' spots along the photos. But my mind tells me the underlying is just decanted (not sublimating) material. To even admit it as a possibility, the pixels should really go to the top of scale.

        Do you realize we are 'chewing' the possible nature of something represented by a handful of pixels?

        Thanks NAVCAM team.


  • Emily--

    Thanks for posting today's images. Keep the good ones coming....

    The dominant process on the comet today is the LOSS of material by evaporation and venting of gases during perihelion passage. When this occurs, the interior layers are exposed. Much of the "shelly" and layered appearance of the surface may be due to buried crater "roots" that are now being exposed.

    During the formation of the proto-comet some 4.5 Gyr ago, it grew by accretion of smaller bodies. Many of the boulders now weathering" from the interior may be more-or-less intact example. The small impacts are loose and rather fluffy icy conglomerates. The comets we see today are those proto-comets that, by chance, grew largest, and their gravity, though weak, helped them grow fastest. Formation by accretion is standard model that for asteroid, planets, etc.

    In the temperature regime of the comet formation, however, low-speed impacts shock and compress the material under the impact, producing local fusing of the fluffy substrate into a flattened or bowl-shaped structures, while expelling an ejecta cloud that may have re-impact the comet elsewhere. On asteroids, the magma formed by impact is never excavated; on icy comet bodies, the impact hardened disks and bowls are buried and only partially broken up by later impacts. The interior of a comet is thus composed of relatively hard "bowls" of resistant material embedded in a matrix of softer, fluffier, icier material. Because mass LOSS is the dominant process on a comet, we can view the interior structure of the body in a way that we do not see on asteroids. On asteroids we see the final surface; on comets, we see exposed the interior structure of the body.

    Thus the comet is a rubble pile, and the loose rubble is interspersed with layers and shells of resistant material. And the softer stuff is now being evaporated or sublimed away. Rimmed bowls like the pristine one in the photo posted today suggest that ancient impact events created circular shells of shocked ice that were buried during formation, and are now excavated as the comet disintegrates. The elevated "mesas" and "buttes" are more fully exposed impact roots. The circular rings resemble the once-buried and now-excavated Gosse Butte impact crater in Australia.

    Of course, some of the oval, cliff, circular surface features may be caused by local collapse of the surface, and some other circular features appear to be deep vents, perhaps associated with jets.


    • Rob says:

      Excellent description of comet formation and morphology - thank you for this.


      • THOMAS says:

        No, Rob. It's simply a description of the current THEORY of comet formation and morphology which the Rosetta images have now falsified. It's a mere statement of faith, a simple reminder of the mainstream party line. If Richard Berry's detailed description were already accepted as known fact, then why on earth did we even bother to spend 20 years and billion of dollars sending Rosetta to get these astounding hands-on images and information, which NOBODY in the mainstream community expected?

        • Rob says:


          I'm not going to argue this pointless toss with you - I'll simply say that your remarks show you up as misguided, purblind and out on the very shaky limb of your faith-based, uncountable-times-disproven pseudo-science. Mainstream physics - and your pet hate astrophysics - are mainstream for many very good reasons, and this you simply cannot accept. That is your problem, not that of mainstream science, and certainly not that of the readers of this blog.

          Here's a worthwhile suggestion - get some sponsors, get some engineers to build your own craft, fly it to a comet and conduct whatever activities you and your battery-driven Electric Universe buddies can think up to prove your own, ahem, "theories". Good luck with all of that. Afterwards, you can astonish the world by publishing your findings in whichever tin-pan-alley, peer-reviewed-only-by-your-pals journal, or crank website, will be willing to host them.

          Meanwhile, do continue to amuse us with your held-together-with-duct-tape ramblings...


          • THOMAS says:

            Thanks for all the compliments, Rob.

            I'm not prepared to argue the toss either, since it's the hands-on data currently being collected by Rosetta (as yet undisclosed) which will eventually settle the debate one way or the other. That is precisely the "point" I'm making. I can wait.

            I just stick to facts and my understanding of the scientific method is that theories stand or fall by them. And the fact is that the images coming back to us from Rosetta (even the ones that are being carefully selected for our public consumption) are doing nothing to prop up the "dirty snowball" THEORY, whether you like it or not.

            You didn't answer my question,BTW: "If Richard Berry's detailed description were already accepted as known fact, then why on earth did we even bother to spend 20 years and billion of dollars sending Rosetta to get these astounding hands-on images and information, which NOBODY in the mainstream community expected?"

            Too hard a question to field, no doubt. Much easier to hurl abuse, I guess.

            Stick to the facts, Rob.


    • Robin Sherman says:

      Thats certainly what the pictures are telling us so far Richard. It is surprising given the tiny escape velocity of the comet ,how much ejecta is spread over the surface of the comet if that is indeed what the flatter, smoother "plains" are made of. The jets we see appear to have very significant velocities since they are so straight.

      Looks like we are going to have to wait until November 12th for an overview of the science conclusions so far, and we are promised OSIRIS pictures and Philae pictures of the landing are going to be made public "As Soon As Possible" at that point, data rates permitting.

      Meanwhile we just have hope that Emily can pry a few more amazing pictures out of the team. They are it seems fascinating not only to us as enthusiasts, but to the wider public, children in particular, which is great.

      Congrats to ESA and all the Rosetta team!

    • logan says:

      Beautiful, indeed. But impact mechanisms doesn't bring this highly structured 'fractal' geometry below of the craters. Are, in your model, a kind of thermal flow, after impact phenomena?

    • logan says:

      Hi Richard.

      '...while expelling an ejecta cloud that may have re-impact the comet elsewhere.'

      When imagining fusing impacts I don't expect re-impacts.

      • logan says:

        Really Richard. When thinking of impacting a ruble pile with gravity forces in the milli-newtons, can't avoid of imaging doom.

        • logan says:

          This things are someway 'cooked', a la planetoid. Came from the coldest places, not meaning they were forever cold.

          • logan says:

            Even ISS external paints are 'cooked' a little on every solar storm hitting. I imagine this process extended to billion years.

            There a lot more than 'rubble' out there. Organic molecules could sinterize on powerful adherents.

            'Rubble' tag offends me. 😉

    • Bill says:

      I think you have it nailed. A comet accretes from the primordial solar nebula (or before) by various unknown processes. The composition is silicate dust (pyroxenes and olivines), water and various gases containing C, H, O and N. And at this point we do not know any of the details of this accretion process, but we can see many tantalizing clues on 67P.

      As the comet heats up approaching the Sun, the gases sublimate, driving the fine nano-scale silicate dust from the surface. Thia dust forms the dust tail we see telescopically and the gas forms the ion tail by interaction with the Solar wind. And some of the larger entrained duat particles fall back to the comet creating the smooth. blanket overlying the rocky surface. I think of it as a deflationary process, with many variations on that theme.

      It's a fascinating new world.


  • Marco says:

    I think they might not be "loose boulders" but protrusions from beneath, securely attached to the comet. 🙂

  • Clive Hartland says:

    I am amazed at the imagination of some people as they describe electrical discharges and other Phenomena.
    The erosion of the neck is proved by the fact that there are gas jets and materiel is being ejected from the core via the neck! The Comet 67P is very old and this has been going on for millennia.
    What is not clear is what is generating this out gassing of materiel.
    My own idea is that there is an incandescence in the middle of the Comet but the cause and function is a mystery yet.
    I would feel that the Scientists and Geoligists are very surprised people at this time as they did not expect to find and active Comet but expected to find a frozen lump of ice and play with.
    The Coma and tail of a Comet has now been explained as it seems all Comets are active and not dead.
    Philae will land safely it is hoped and a lot more will be explained as it probes the Comets secrets.


    • logan says:

      Your model talks of radioactivity? Actual instruments could easily spot it.

  • Rob says:

    "My own idea is that there is an incandescence in the middle of the Comet" No - the jets are caused by outgassing of ices sublimating directly into the vacuum, and this is driven solely by solar radiation impinging on the surface of the comet. The comet has no mystical hot center.

    "I would feel that the Scientists and Geoligists are very surprised people at this time as they did not expect to find and active Comet but expected to find a frozen lump of ice and play with." - You're half-way there - they certainly did expect to find a frozen lump of ice and dust, the activity of which (outgassing, tail, etc.) would be dependent on the amount of solar radiation impinging on the comet at any point in its' orbit around the sun. And that's exactly what they found.

    "... it seems all Comets are active and not dead." - Correct; it's just when they're far away from the sun, their activity is low, or VERY low, depending on how far they are from the sun. 67P's activity is now picking up to the extent that Rosetta's cameras are now registering outgassing and jets.

    W'hat a marvellous space mission - GO Rosetta!

    • THOMAS says:

      « ...they certainly did expect to find a frozen lump of ice and dust […] And that's exactly what they found. »

      As in this picture, for example?:

      Are all those rugged, jagged, stratified features the "ice" or the "dust"?

      Please stick to the FACTS, Rob! However hard you try, you can't fool all the people all the time into thinking that black is white.

      • Robin Sherman says:

        As I understand it Thomas your position is therefore, "If it LOOKS like rock, it is rock". Perhaps you should review the results and pictures from the Huygens probe to Titan.

        • THOMAS says:

          Spot on, Robin Sherman! I couldn’t have phrased it better myself. Many thanks for asking the right question!

          In our modern world of fantasy, virtual reality and unfalsifiable scientific theories, I still indeed honestly believe that if you see a close-up photo of a guy holding a smoking gun, then he’s probably just used it to shoot somebody or something. Even if he were my best friend, I would probably be forced to give up on claiming he was just watering his lawn with a garden-hose.

          IMHO, the images ROSETTA has been sending back to us for the past few weeks (even the frustratingly few which have actually been disclosed), like this very old one now, from over 6 weeks ago: look as much like pictures of stratified rock formations as in the thousands of photos that tourists take of the Grand Canyon every day, for example (chosen completely at random from Google images): / . (Just flip it 90° and zoom in…).

          I just happen to believe (as you suggest, as if there were something perverse about the idea), that what looks like rock probably IS rock. (I’ve walked down into the Grand Canyon and back up again and that was enough to convince me that it wasn’t made of ice, dust or marshmallow). It’s called hands-on evidence, which we’re also now getting back from Rosetta: if it looks like rock, then it is rock. I still have a naïve faith in the idea that it’s the hard evidence you acquire which is the very basis of the so-called (and currently forgotten) “scientific method”. But it’s true it took me a few years and quite a bit of training to get rid of the distorting filter of those preconceived ideas we call “theory”.

          As for the “pictures from the Huygens probe to Titan” you refer to, many thanks too for reviving that particular memory. I still vividly remember sitting in front of my computer screen at the time and being astounded, like everyone else, as those first pictures came in of small rocks chaotically littering a desert plain:

          We’ve since had very similar pictures from (amongst others) the Mars Curiosity mission, for example:

          In short, rocks and boulders everywhere, just like on Rosetta’s comet (can’t wait for the close-ups…!)

          What was the point you were you trying to make, actually?

        • THOMAS says:

          What is your source, please, for your statement that those rocks on Titan are made of ice? With what degree of confidence does your source advance this bizarre idea,and on what basis?

          Personally, I've never, ever seen a single chunk of ice which looks like a rock but perhaps I just don't get out enough. In the picture I linked to, there are hundreds of rocks. And they're all supposed to be lumps of ice? Who's trying to make us believe black is white, and for what purpose?

          • Robin Sherman says:

            Once again I refer you to the Huygens mission.


            To save you the trouble of reading through it all.

            "Instead of liquid water, Titan has liquid methane. Instead of silicate rocks, Titan has frozen water ice. Instead of dirt, Titan has hydrocarbon particles settling out of the atmosphere, and instead of lava, Titanian volcanoes spew very cold ice."

            I have no problem with you questioning currently accepted theories, it is part of science history that such doubt has brought progress. However that history also has constructed a huge self consistent, proven by experimental measurement, construct of the world around us. Where is the cut off point? Presumably you take the laws of Electromagnetism to be true, since you believe so much in electrical phenomena. It seems that you do not accept General Relativity and its results and conclusions, even though it too has been proven by experimental measurement.

            It comes down to what evidence you accept other than your own personal experience. I'm willing to accept the scientific community has measures and systems in place to ensure the integrity of science and so am prepared to accept the current mainstream models as the starting point for further advance. That does not mean they are correct, or that I think they are correct, but practically and intellectually we are in no position disprove the current accepted theories. Your views are based on what you know and accept, mine are based on what I know and accept.

            Small objects orbiting the sun made mainly of rocky material are called Asteroids. Those made mainly of ices are called Comets. If you wish to argue Rosetta is in orbit around an asteroid, then do so. In which case, ESA has made a pretty fundamental error.

          • THOMAS says:

            Thanks for the link, Robin S. Don’t worry, I’m a compulsive reader anyway but in this case I also read the whole thing to get the context. I note, above all, that your press release was issued back in January 2005, just a week after the Huygens landing. The findings could hence presumably only be provisional. Perhaps you shouldn’t accept as fact what was clearly only hasty first-guessing based on theoretical expectations. I don’t.

            More relevant to our discussion, I think, is this NASA release I just found from nearly six years later, dated November 2010,, which quotes the authors of the study in question as saying, much more tentatively, that “Titan's rocks are BELIEVED to be made primarily of water ice frozen into a hard mass about minus 180 degrees Celsius (minus 290 degrees Fahrenheit), RATHER THAN Earth's mineral rocks” (my capitals, for emphasis). After over five more years of further research compared with your link, the article cannot be said to exude huge amounts of certainty or confidence on the part of the research team. The conclusion is “The radar team PLANS TO CONTINUE LOOKING for other instances of small, smooth spheres in nature TO INCREASE THEIR CONFIDENCE ABOUT THE EXPLANATION. They also said MORE STUDY IS NEEDED on the mechanical properties of water ice at such cold temperatures.” (my capitals, for emphasis).

            Suffice it to say that if even those NASA people most closely involved with the Cassini mission are, six years on, so lacking in confidence in their “findings” (which still need a lot more work to try to confirm them), then I don’t see why I (or anyone else, for that matter) should be convinced by their hypothesis either. Personally, I still believe that when we see pictures of what looks like rocks, whether it’s on Earth, On Mars, on the Moon, on Titan or on the five comet nuclei we have so far acquired images of (and whatever the temperature), then they are indeed mineral rocks, not “water-ice rocks” (whatever THEY are!) And I find the contortions which are routinely made to try to fix the facts to fit the theory initially amusing but ultimately extremely worrying.

          • THOMAS says:

            Concerning two details:
            - I naturally “take the laws of Electromagnetism to be true” because the reality of the “electrical phenomena” you refer to is increasingly being established as a fundamental mechanism in every branch of what used to be called the “natural sciences” (before theoretical maths made its successful takeover bid…). It ranges from the infinitely small (probably even going way down below the electrical workings of the living cell which research in the field of molecular biology is increasingly revealing to us) up to the infinitely large in the workings of the Universe as a whole. Basically, I think that Nature (or whatever we call it) is extremely lazy: it’s that tiny force exerted by a plus on a minus (and vice versa) which, in one way or another, organizes EVERYTHING from top to bottom (including even gravity, in ways we don’t yet understand and perhaps never will do completely; in any case, presently we don’t have the faintest idea of what gravity is…). I think this sort of holistic approach could go a long way to solving the long-standing problem of finding a unifying principle to reconcile apparently disparate forces (the four basic forces) or mutually incompatible theories (Relativity and quantum physics).
            -I don’t, indeed, “accept General Relativity and its results and conclusions” as anything other than a theory which can also be falsified by observation. In this connection, some of the more spectacular observations which have been held up as providing definitive confirmation of the theory (“gravitational lensing” of quasars, for example, as in the “Einstein Cross”) don’t in any way confirm the theory at all, quite the contrary. I’m far from being the only one to have such heretical thoughts:

          • THOMAS says:

            Robin S, as regards your final point about what you seem to consider as a fundamental generic difference between comets and asteroids, perhaps you should read up on the Centaurs (half comet –half asteroid bodies on eccentric orbits)…. For a mainstream view, I suggest this recent NASA press release (note the bewilderment…) and for a more hard-hitting dissident interpretation, try

            Which brings us back to the Rosetta mission…. The only-recently-acknowledged hybrid nature of certain asteroids which at some point in their orbit “inexplicably” start to demonstrate cometary behaviour with a full- blown coma tail provides even more forceful arguments for the “electric comet” theory. Their behaviour (naturally baffling to the proponents of the standard theory) seems to confirm that the ONLY fundamental difference between asteroids and comets is the shape of their orbit: asteroids are lumps of rock with standard, relatively circular orbits round the Sun while comets are lumps of rock with eccentric, more elliptical orbits round the Sun, causing them to undergo an exponentially increasing electrical charge imbalance. They can only return to a state of equilibrium (as Nature will always have it) via electric discharge. It’s the phenomenon we know as “lightning” down here on Earth and which we are currently (pun intended) observing on 67P/C-G (after observing them on the other four comet nuclei we have imaged) in the shape of those long, dead straight “jets” we observe. Asteroids become comets when their orbit round the Sun is altered, not because the rock they’re indisputably made of has been somehow magically transformed into dirty snow or ice!

            I’m confident that the findings of the Rosetta mission, once ultimately disclosed, will tend to confirm this theory.

        • THOMAS says:

          And are you seriously suggesting that all that rock visible on Comet 67P is also ice? Nobody else is (at least for the time being). What's the deal?

          Or perhaps you mean that, as in the case of the Cassini mission, in a few years when all the fuss has blown over and most people have forgotten all about it, we'll be quietly told that everything we thought was rock on 67P, like on Titan, was actually ICE? I won't swallow that one either.

          So what scientific point are you making exactly?

      • Rob says:

        Thomas - the facts are these - there's plenty of gases and ice out there in space, plenty of dust, plenty of mixing of both in discs surrounding protostars and early main-sequence stars, plenty of planets, planetoids, asteroids and comets forming within these discs. How can dirty iceballs NOT form in such circumstances? Gravity and intermolecular forces hold these bodies together, unless or until they spin too fast, or collide with other bodies, or are disrupted by tidal forces. Comets simply cannot be anything else than simple agglomerations of ices, dust and rocky detritus. No need to invoke fairies, unicorns or electric universes to explain things.

        That much is certain - what's not known are the details: what ices/gases are present in the comet body; the proportions of ices (water ice, frozen gases) to rocky materials; the isotopic ratios of the various elements in the materials bound up in the comet; does the comet contain any complex organic compounds; if so, the chirality ("handedness") of such compounds can be tested; determining the noble gas content in the comet body/ejecta; the precise mechanisms by which the surface- or sub-surface ices manage to escape the comet body; the energy balances between incoming solar radiation and outgoing gas/dust; what effects the solar wind and magnetic field have on the comet and it's ejecta; determining the internal structure of the comet body by radio waves, and so on.

        Both the main Rosetta craft and the Philae lander have purposefully been equipped with the requisite instrumentation to provide data which will hopefully lead to answers to these questions. I say purposefully - what you so disparagingly term "mainstream" scientists have pooled their knowledge, skills and wisdom to build a beautiful and complex set of machinery, sent it on its' way on a voyage of many hundreds of millions of kilometers of deep space, lasting over a decade, to arrive at its' destination fully equipped to investigate the comet in great detail. The only real surprise for the team, and the rest of us looking on, is the unexpectedly peculiar shape of 67P/C-G, which will have its' greatest impact on the (hopeful) landing of Philae.

        So, no: you're wrong. There are no great embarassing holes in any "mainstream" theories, no red faces at ESA/Rosetta headquarters, no rush to contact your good self to get them out of a fix which they could never have imagined in their wildest dreams. It's really business as usual: the political will of the countries involved in ESA to fund the application of deep knowledge of physics and engineering, years of training, competence, skill, good judgement, great planning and teamwork and - what's missing in your pitifully 1 1/2-dimensional view of things: imagination - the stuff of dreams come true.

        Welcome to the REAL world, Thomas.

        • Marco says:

          Rob. When you say "Comets simply cannot be anything else than simple agglomerations of ices, dust and rocky detritus."
          You really mean that comets could only have *started out* as simple.... They are clearly now complex, evolved objects with bi-lobed shapes more often than not, pitch black exteriors, discrete jets, cliffs, scarps, and other geometric features. It's emissions are of different elements and compounds than its visible exterior indicates. Data indicates liquid water processing in its past, when logic dictates only solid ice is possible because of the vacuum of space. Also it's solid monolithic looking exterior is incompatible with a "rubble pile" and a density a fraction of that of water. All in all comets look different from what logic and science tells us they should look like.

          • THOMAS says:

            "All in all comets look different from what logic and science tells us they should look like."

            Marco, I'd have said rather: "All in all comets look different from what standard theory tells us they should look like."

            It's not a question of "logic" here except for the internal logic on the theory itself. But that's a circular argument, it just isn't science. At some point, according to the scientific method, the theory is quite simply falsified by objective, external evidence which refutes that theory's internal logic.

            And what you accurately describe above is actually doing exactly that...

        • THOMAS says:

          Don’t worry, Rob, I know all about the theory of planetary formation by accretion. Just don’t tell me it’s FACT. Your argument is totally circular: OF COURSE everything MUST have happened exactly as you describe it IF (and only IF) mainstream Big Bang theory is CORRECT, quite simply because THAT IS HOW THE THEORY DESCRIBES IT.

          But whether you like it or not, your theory, like any other theory which aspires to scientific status, must be FALSIFIABLE by any observed contrary evidence which proves the existence of OTHER mechanisms, thereby giving rise to a more SCIENTIFICALLY ACCEPTABLE theory. (I trust you learned about the requirements of the scientific method at school or in college). That is precisely the question which is currently being posed in a particularly challenging way by the images and data coming back from Rosetta, just as it’s being challenged the whole time by countless other observations.

          Take, for example, the data on the workings of our nearest star, the Sun, which have been baffling mainstream astronomers for several years now, ever since images started coming back to us from SOHO: how does your theory explain away the Sun’s astounding inverted temperature curve compared with mainstream expectations (over 1,000,000 K way up in the corona, compared with a paltry 5,700 K way down below at the visible surface of the Sun, in the photosphere)? Sorry to challenge you with mere facts, but if actual images and data have now become such an embarrassingly challenging problem for current astrophysical theory, I suggest we simply cut short all planned and even ongoing missions, including ROSETTA….

        • THOMAS says:

          Actually, I know exactly where you’re coming from Rob, since I was there myself around 15 years ago. I can assure you there was no more convinced and supportive mainstreamer than myself at that time. You shouldn’t so naïvely believe that non-believers-in-the-official-doctrine are necessarily young, ignorant, misguided or brainless iconoclasts. Personally, I’m over 60 and I’ve led what most people would call a highly respectable academic career in applied research. I know how to think, I know precisely what the scientific method is (or should be!) and I know how to apply it. Do you?

          The fact is that after several decades of closely and trustingly following developments in astronomy back in the 20th century (including the Apollo Moon missions in my youth, of course…), I finally started having doubts about the validity of the established BB paradigm after realizing that the PICTURES and what they implied were stubbornly refusing to confirm the THEORY. Worse, the theory was being forced to make ever more comical contortions to attempt to explain away the observed data which mainstream astronomy was literally “in the dark” about, by inventing those beautifully convenient but unobservable, hence unfalsifiable, concepts: “black holes”, “dark matter”, “dark energy”, etc. (I guess that’s what you mean, BTW, when you speak, at the end of your post, of the need to use “imagination” to create a good theory. I hope you will eventually learn that scientific theory stands or falls SOLELY by the validity of the FACTS which give rise to it and that the need for excessive “imagination” is simply a euphemistic excuse for either “dreaming up” mere science-fiction or for patching up a failing theory. If you think that’s the “real world”, I don’t, but you’re welcome to it. It’s not for me).

          I would have thought that after many decades now of fruitless observations and futile theorizing about the nature of “dark matter”, we could safely conclude that it simply doesn’t exist. We should perhaps all grudgingly accept the idea that the inexplicable observation (inexplicable to mainstream, “gravity-only” thought, I mean) which gave rise to the invention of the concept of “dark matter” in the first place (i.e. the apparently “anomalous” rotation of spiral galaxies, with the athletic outliers effortlessly keeping pace with the hundreds of billions of other stars more fortunately placed on the inside lanes in each galactic sports arena) is in fact driven by the overwhelmingly dominant role of electricity in the Universe, exactly as if it were a homopolar motor.

        • THOMAS says:

          Which, to conclude, brings us back to the Rosetta mission…. The problem I haven’t yet seen addressed on this forum is the fact that however competent, highly-trained and totally sincere the scientists who planned this mission are (about which I personally have absolutely no doubt, on any score), the unfortunate fact remains that the planning phase they conducted over the ten years between 1994 and 2004 necessarily dates from an epoch when we had obtained a lot fewer images and much less data about comets, the only previous images of an actual comet nucleus being those of Comet Halley, acquired by ESA’s Giotto probe in March 1986…. Since 2004 when the Rosetta probe was launched, we have acquired extraordinary images of three more rocky comet nuclei (Comet Tempel 1 of “Deep Impact” fame, in 2005 and again in 2011, Comet Wild 2 in 2004 (but we only got to start analyzing the highly problematic “stardust” it was sent to collect as of 2006…), and the peanut-shaped, dry ice spitting Comet Hartley 2 in 2010), which have all provided extremely challenging data for mainstream theory to try to account for. I haven’t yet seen any sort of satisfactory explanation, for example, for the double flash recorded on images of the 2005 encounter of the tiny copper “impactor” with Comet Tempel 1 which was the undisputed highlight of the “Deep Impact” mission (and which, incidentally, had been PREDICTED pre-impact by the “Electric Universe” people)

          Consequently, all the thinking which went into the planning of the ROSETTA/PHILAE mission, however brilliant and scientifically respectable at the time, has necessarily been overtaken by more recent, groundbreaking observations. It’s called history in the making and it’s probably a unique case in human history of scientific theory being definitively overtaken (not to say swamped) by more recently-acquired scientific fact, thanks to the exponential technological progress currently being made in every scientific field on Earth.

          Rob, you will presumably realize in time (pun intended) that the FOURTH dimension, time, is by definition crucial to the progress of human understanding. For your own sake, I sincerely hope you’ll eventually leave your current Dark Age science-fiction ideas behind and go beyond them to enjoy the light which comes with the correct application of the scientific method. Welcome to the real universe in FOUR dimensions!

          • THOMAS says:

            Sorry, that last sentence should have read: "For your own sake, I sincerely hope you’ll eventually leave your current Dark Age science-fiction ideas behind and go beyond them to enjoy the Enlightenment which comes with the correct application of the scientific method. Welcome to the real universe in FOUR dimensions!"

  • logan says:

    Wonder if this 'clam' like structures are kind of related to long gone craters.

    Just right of top 'collapsed' crater.

    Being x axis 100, at 65,20 and suggested just below dust at 22,46.

    (As image tech custom, being upper left corner 0,0).

    Have seen in another photos, too.

  • Bill says:

    A couple of observations on the North Polar Jet we've been monitoring the past few days--

    Looking at it from the side-- "90 degrees longitude" the jet looks narrow and well-defined:

    But getting a little over 90 deg longitude to the south, the jet becomes less sharp and defined:

    and looking at it from 0 deg latitude (the front), it becomes very broad:

    What I propose is that North Polar Jet is actually a broad, fan-shaped jet elongated along the 90 deg-270 deg longitude plane (east-west?). Viewed from the "side" is is very sharp and distinct, but viewed from the "front" is is very wide and ill-defined.

    This tells us volumes about the nature of the set of vents that produce this feature.


    • frankebe says:

      "...this tells us volumes..."

      OK—Like what?

    • Robin Sherman says:

      Bill having seen your pictures, I have tried looking for any signs of vents in the plain/neck region. Below and just to the right of the collection of the biggest "boulders/crater remnants" there a number of small depressions, some in groups, the most visible are in a linear arrangement running pretty close to east/west.

      There is another area containing several smaller "dimples" in the far right corner of the valley, one large one appears to be at the centre of the very bright spot close to the cliff. Similarly there are some more "dimples" on the outcrop highlighted in your pictures. There is another line of white surrounded pits at about 11 O'clock on the rim of the huge crater centre picture. It is similar to the straight line Logan spotted.

      As Emily says it is difficult to say if these are small impact craters or depressions, created as gas sublimating from just below the surface, means the dust has sunk down to fill the void.

      Surface dust would facilitate chemical reactions with the solar wind/cosmic rays, sintering as Logan calls it, as seen in interstellar dust clouds, to create the dark organic type material suggested by the Rosetta team.

      The surface dust may not come just from the comet itself, but be slowly swept up as the comet orbits through the zodiacal cloud. The very low gravity would mean this layer of dust would not be compacted and remain light and fluffy. Any ices contained in this collected material may explain the beef period of bright activity in April/May as the solar radiation reached an energy level sufficient to evaporate this very thin layer of surface ices. This would match the evidence of a dry, porous, very dark surface outlined by the science team earlier.

  • Henk says:

    The pictures are absolutely unbelievable. This is really one of the most interesting and most incredible space science missions ever (water on earth possible coming from ancient comets some from before the solar system/building blocks for earth life possible coming from comets, the never before seen close up comet views, the comet tail buildup over the next 12 months, etc, etc).

    And to know these are only the navcam images and we have to wait for most of those much sharper Osiris images (some 6 months according to some?).

    While a very large part of the science can be done from the orbiter i`m really hoping the lander makes it down as well. The risk with such a strange object and all the unknowns are just so high that i`m not going to expect it. It just would be a Christmas bonus beyond belief.

  • Dave says:

    ESA nice to have some text with the pictures, but tell us the story behind it instead of an uncommitted look at this.
    Please tell us some facts
    Also more and more stories of sublimating ice under the surface are just not supported by the visuals. There are many deeply cut features, if there was ice it would be exposed every where but it's not even detectable with your sensitive instruments. Please tell us what the dust collected is made of, show us the pictures of the columated high speed jet streams and show us the sublimating jets and the holes they come from. Are they rifled to get such parallel emission or some other novel form that can be generated purely by sublimation, good luck

  • Erich says:

    Sublimation is a phase change from solids to vapours or a vapour to solidify without ever getting into a liquid state.

    H2O does this trick at a pressure under 6 mBar and a temperature under 0 deg C, its called the triple point. (Most substances can do this but not all of them can melt and for a while ago scientist thought helium could not freeze).

    Just a note,,,

    • Robin Sherman says:

      The lowest temperature pure water can be liquid is 250.16K at a vapour pressure of 209 Mpa ( ~2 atmospheres). The important thing is the vapour pressure above the water/ice. As mentioned above, impacts provide heat and pressure, liquid water at impact sites would seem to be possible. The sublimation would be very rapid in a vacuum creating, at least close to the comet surface, a significant vapour pressure, allowing the liquid to remain for periods of time.

      The large eroded impact craters "revealed" all seem to have flat bottoms, without the central peaks often seen in impact craters on rocky bodies, so I'm guessing the bottom of the crater would fill with liquid, find its level and then solidify as a very compact ice, the lighter, more volatile components having boiled away. There are any number of examples of this all over the comet, the rims of the craters being made of compressed denser ice are slower to sublimate as are the flat floors.

      For very large impacts such as the one on the equator on each lobe, there could be enough liquid to "slosh" over the edges of the craters and create flows on the surface. When the comets gets closer to the sun, the rate at which ice sublimates and an increase in surface temperature could also create the conditions for liquid water to exist. The surface temperature is already 220K in places we are told. The key is the vapour pressure at the surface, which hopefully Philae will measure.

      Well its a vaguely plausible theory anyway. Not much else to do in the absence of any coming from the Rosetta team.

      Have you got a volume from your digital shape model Mattias?

    • Sovereign Slave says:

      Thanks for this explanation, Erich. This point has been very confusing to me as far as how water could account for the comet's coma through sublimation. If the comet is mainly ice and rock, and it's the ice that mainly accounts for the tail, and as comets don't have internal heating systems that we know of, all the required heat must come from the sun. When I read articles like this:, which was well over a month ago, the average temperature of the comet was minus 94F, yet it was already sublimating. In my world water is still very frozen at -94F, what exactly makes the water change from being frozen in the comet's world at that incredibly cold temperature?

  • Lynn says:

    Anyone care to guess what orbital plane Rosetta will be flying on the release of Philae. Also why release at 22.5 KM, seems like greater accuracy would be achieved at a lower altitude.

    • THOMAS says:

      Obviously there would be exponentially greater accuracy at half the currently planned release altitude. From 22 km, touchdown anywhere near the centre of the chosen landing site is clearly just a lottery.

      But I seem to remember it was said in one of the recent releases that Rosetta would only attempt to go down to 10 km if it was judged safe to to so on the basis of the collected data. That is now clearly not the case, but we're going to have to wait months or years to be (perhaps) told exactly why.... My bet is on those pesky electric discharge machining phenomena which are likely being detected all over the place.

      In my view, Philae unfortunately thus has scant chance of safely making it down to the surface and sending us back the data we'd all love to collect..

    • logan says:

      From what has been told here, it seems that an impact is actually needed, as the planning goes.

    • Lynn says:

      Are we in a quiet period. Have we inserted into the 20KM orbit?

  • Dave says:

    Most people have a good idea of sublimation, as it comes early in chemistry and physics.
    The problem is there appears to be no water beneath the surface, even NASA scientists said tounge in cheek we know the ice is there but it's just well hidden.
    So with out ice what's to sublimate and what gives the illusion of water in the tail?
    Is Rosetta bathed in water or bathed in hydroxils of indeterminate origins ?
    We can not answer this which ever side of the fence you are on because no data is being released,
    So if there is water ice lets have it detected, if there is electric machining then let's have it detected, there are enough instruments running to give real clues.
    I don't mind what the answer is, just let's have the data so that we cAn all agree the basics and move on

    • Denis says:

      Move on?
      Rosetta just got there and is going to stay for one more year. Do you expect final conclusion after one month there ?
      I expect partial conclusion in a few years time 😉

    • Robin Sherman says:

      As the Rosetta science team explained it, the surface is covered in a layer of dust containing many organic chemicals (hence the black "colour"). The dust is very fine and the low gravity means it does not get compacted and is therefore very porous or "fluffy". Any ices in this layer would have sublimated away as it is easy for the gas to escape. hence no water/ice visible on the surface. This layer varies in thickness over the comet as we see in the images.

      It's porous nature means it acts like an insulation layer, with lots of tiny spaces filled by vacuum. Conduction of heat through this layer is hence very slow and radiation nearly all absorbed at the surface.
      However, even at very low temperatures, in a vacuum, the ice will still sublimate at the boundary of the two layers. The porous nature also means that very small amounts of sublimating gases seep through the surface layer to create the coma that Rosetta has detected. This is the evidence that ices are below the surface layer.

      Highly contrast stretched images do indeed show a thin icy halo above the surface of the entire comet. Harder to explain are the large clouds/jets seen in these images.

      Much of the instrumentation on Philae and some on Rosetta are specifically designed to work out the thermal conductivity of the surface layer and the temperature gradient as you move through it down into the comet. In other words how much heat/energy actually reaches the ice below.

      That was the official preliminary explanation, there are it seems plenty of areas where surface coverage is minimal, cliff faces, crater rims and "boulders" where this reasoning does not apply. Unfortunately these are the areas Philae can't land on and investigate.

      We await enlightenment.

    • THOMAS says:

      Hear, hear, Dave!

  • WJ says:

    download the .mov file, play it with VLC - loop, slightly reduced speed, full screen

    The shadows don't move on 67P -> ovserver is moving.

  • logan says:

    ...The processes appear much more complex than a simple model can explain...

    Thanks a lot for that, Marco.

  • Kamal Lodaya says:

    We have had a few pictures and a lot of discussion on the "front" of the neck. Until a few days ago Rosetta hasn't been to the back but from the rotation of the comet do we have any pictures of what the "back" of the neck looks like? Does it have a similar structure, or is it different?

  • Kamal Lodaya says:

    The picture on 3 August seems to be the one where some of the "back of the neck" is visible. (To some extent also 19 September.) The smooth surface visible at the front of the neck (on which the "necklace" of boulders lies) extends farther, but does not seem to extend all the way around, although it is hard to be sure because of the shadows.

  • Dave says:

    To robin s
    I understand the theory you describe, that does not make it right, you have to question the data as it comes
    The belief that the tail is sublimated water seem to stretch fActs, there are H and O detected but on previous missions not in the right proportions to have come from water.
    The temperature and pressure appears to rule out sublimation, so why can we believe the tail is from sublimation?
    So why are we so sure that sublimation is occurring below the surface?
    ESA has instruments that are attempting to see the structure beneath the surface right now. With such a key plank of the theory depending on water ice, you can bet the would of a lived to the universe if they found it, so it looks extremely unlikely the longer we look.
    The composition of the dust and the structure (has it been heat cycled) will have been determined by now but no data has been released let us make up our own minds.
    If you have some science training it's good for a while to let go of the straight jacket of a theory developed way before we could get close to a comet.
    This is the real deal, the comet looks completely different to what was expected, so let's open our minds and assess the limited data as though we came across it for the first time.
    If you did would you really come up with the current theory?
    Electric theory may not be right ether but let at least be guided by some sort of factual analysis

  • Marco says:

    You're welcome Logan. I didn't really want to get into my pet theory, which involves liquid water within the comet, teeming with microbial life.. Oh and a giant amoeba. 😉 in fact the whole comet is reproducing into two, with a giant amoeba in each. Makes electric comet theory appear like a simple, logical model.

    • logan says:

      Welcome, you other Marco.


      • logan says:

        Really believe on determinacy of electric processes. Happens that I'm not just a 'believer'. Please easy up. (Really liked your joke).

        • logan says:

          (Even believe on relevant electric phenomena during accretion). Now the other side can hit me too.

          • Marco says:

            Logan, my pet theory is greatly at odds with both standard cometary theory, because it assumes sublimating ices, and at odds with electric comet hypothesis, because it assumes dry rocky electric body.
            I am much more favourable to the panspermia theories on comets - ie. that they have undergone a phase change to a liquid water core, that living organisms inhabit the comet and that the surface is organic cemented material from those organisms. The surface absorbing enough energy, and sealing off enough pressure for the liquid core to stay liquid.
            Also, in cases where comets have "split up" what we see is when comets that have already separated move quickly apart due to tidal or aerodynamic forces. The actual separation is very gradual and comets go from roughly spherical, to peanut shape, then dumbbell shape before they separate, then rely on close encounters with planet's tidal influences to have separate heliocentric orbits.

          • THOMAS says:

            Marco, the electric comet hypothesis doesn’t "ASSUME" “dry rocky bodies”, it was born of, and is reinforced by, actual observation of things like the rocky comet nuclei we have so far imaged, which all happen to be black, dry, ice-free and totally rocky. There may well be ice, water, whisky or your favourite barbecue sauce under the visible rock (as in this view, for example:, but why should there be? The pictures speak for themselves and leave little room for pet theories (or even the standard theory, for that matter…).

  • Dave says:

    Robin S
    Yes there are theories about the dust, but not all surfaces are covered in dust. Some are freshly eroded.
    ESA by now has very good information on the dust from the coma both chemical. Composition and structure. It has not been released yet, until you get this info I don't understand why you are so sure of sublimating ice . The text book is no good it was written a long time ago before we had such. Good close up view.
    To expect the original theory to be even 50 percent right is asking a lot.
    It is better to look at the data not read the text book.
    If the data was anyway near confirming the std model it would of been stated lowd and clear and celebrated as huge success by now.
    That we don't get to see even the most inocuos data probably means that the ESA scientists are also puzzled by the data themselves.
    Hence whether std, electric, incandescent core or any other theory there is a lot of thinking to do.
    Fore sure the text book will be rewritten, but that's good, we peel off the skin of the onion and it reveals more and more.

    • Robin Sherman says:

      Thanks for your comments Dave. You are right, all my theories are speculation based on meagre facts and I guess on the so called dirty snowball theory, but its fun to speculate. In no way do I assert that anything I post is the actual explanation, I just pose the questions and the maybes. We know that members of the science team are connected to this blog and as you say, appear to be somewhat puzzled, so I see know no reason why we shouldn't add a few of our ideas to the pot, however implausible they might be. The introduction to this blog certainly implies that this is one of the reasons for running it. I am sure members of the team have been doing this since before the mission was designed. Given the unknowns, any weird theory might be the right one.

      You question the presence of water. I point you to Will's post. The science team has outlined the nature of the surface layer and measured water coming from the comet, at 5 litre/sec was quoted by the team. The surface has been shown to be "dry" therefore, the only other place water and other volatiles can come from is below the surface. If there are large amounts of water ice below the surface layer, I speculated how that might happen. The fact that water ice will sublime in a vacuum if sufficient heat/energy is available, is not in question. What does need to be found by the team, is the energy transfer processes involved and whether they explain the observed outflow. The instruments on the mission are designed to answer that question, so I don't think it is unreasonable to outline the process they are there to investigate. It remains to be seen if that process actually is going on, but given the time and effort expended it is a pretty sure bet, the science behind it is valid.

      As for dust. As "erosion" of the surface takes place, which it evidently does and however that occurs, non volatiles, dust, rocks etc., will be left behind exposed on the surface. Others speculated that that material outflowing from vents might contain non volatiles heavy enough to not reach escape velocity and hence fall back onto the surfaceI too. The Earth in it's orbit collects around 100 tonnes of dust a year, it is not unreasonable to suppose in a 6+ year orbit, which also goes through the asteroid belt, the comet will accumulate some dust, ices and rock as well. It stands to reason then, that the surface layer does have silica dust as a component. As I said above, I too would like an explanation for the areas not obviously covered in a thick surface layer, not showing greater evidence of change given the team's earlier explanation. Indeed the visual indications are that the most activity is occurring in areas where there is a visible and thick surface layer. The "plot thickens."

      Finally the argument that if the evidence is there to disprove or prove various speculations made here, then we would have heard about it. We all know the reasons why results and conclusions have not been forthcoming as yet and they are certainly not going to go against that to prove or disprove the speculations of amateurs, however close or far away from the actuality they are.

      The scientific method is to propose a theory to explain initial observations, then make other experimental observations to prove or disprove that theory. At the moment all we have are a few isolated bits of data, known physical processes and some pictures. Speculate and theorise is all that we can do at the moment. As I have already said, "we await enlightenment."

  • Dave says:

    Robin s
    Sorry robin I am in a hospital in Sicily waiting for a flight back home to blighty, I was disturbed a few times while writing. Reading back today I may have lost the thread a bit in a few places

    • Robin Sherman says:

      No problem Dave. Hope things go better for you and you get back in time for the big day in November. That we are told is when the science team are going to give us more science results and initial conclusions. We can only hope some Osiris images come along with that.

      I think the large public interest the early pictures generated took ESA by surprise and the clamour for the science even more so. Given the level of science literacy in Europe especially, I would have thought that would have been expected. They appear not to have had a plan/timetable in place to release such information. I guess they had to wait and see if they could actually get there with a functional system.

  • Dertutenix says:

    This mission will give a few answers but will create a lot more questions. Right now scientists at ESA are hiding behind their proprietary screens trying to find som answers to a few questions, they are not confident enough to deliver a result of theirs studies yet. The conclusion is that it is a lot more complex than we in the public can imagine. Not even high resolution images are published. We can only speculate in vane and fail to get even close to the truth. From ESA an extremely small ammount of data is released, the poor resolution pictures are only nice to look at but tell us nothing essential. Even the figure of mass we in the public had to calculate for ourself from by chance delivered orbital data of rosetta to an accuracy of within 1% instead of wikis within 20% figure.
    Although ESA has a proper figure of its volume they will for some reason not deliver and we have to do an estimate of that as well (21km^3 +/- 15%). On top of this is the fact that this comet is not a general picture of all comets, its just one of a few short orbit time comets and all the other species may and will be totally different. This comet was chosen only because it was in reach for our technology. And so far all that is of essence is that it is black and most likely not made out of cheese at all. That vapor and ice of some substances and at any kind of temperatures are present in comets was known for decades. It would be appreciated if someone at ESA would gain enough confidence to stick out its head and make a qualified estimation or guesswork of an overall image of this comet or at least tell us about when some esential data will be released.

  • Alter Schwede says:

    In November Philae will most likely land successfully and the world wide media will try to make the most of it to sell their products. Some pictures will be delivered and thats it folks! Scientists at ESA will continue their work and the vanishing small minority of the public that has an interest will continue to speculate. NOTHING of essence will hit the head lines. If a follow up mission is ever again planed for i would like to know how it is possible to gain this huge pile of money to finance it when data collected are hidden away.

  • Erich says:

    There is one person out of 50000 on this planet that has an intrest of this mission and likes to get proper information delivered. The rest are not able to read or have no access to media or are only interested to read a short head line but don't understand what it is all about.
    Why is it then so important to keep collected mission data hidden away from those sparse species? Every scientist at ESA has less then one thousend dedicated fans on this planet, how can anyone plan a career when amongst those thousand fans there is nobody willing to spend another euro for further research that is made behind exuses of propriatary rights.

  • james says:

    an amazing advancement in space exploration sciences and a great engineering feat!

  • Frankebe says:

    Although I, too, impatiently await the latest details of discovery, let's be thankful that ESA has put up this blog. I believe they will be telling us what they find as time goes along--let's give them time to do the work! The whole mission is astounding to me, and it goes beyond my ability to express in words my amazement at how great a feat of engineering this all is. So thank you ESA for making any of this available to public in such an informal forum, and I greatly look forward to the next installment of in situ observations!

  • Hansart says:

    Every day I am looking anxiously to see if there is any update on the blog and... I get desperate 🙁
    Last update was posted on 26th of September, today is 2nd of October. Come on ESA team, we are at the core of the operations, please entertain our excitement, and not only our imagination !!!!

  • Erich says:

    The problem is that Rosetta is now at less than 20 km over the surface and again we reached a state where the image resolution is by faaaar too good to be delivered to the public for free. The navcam can do a 4*4 binning and we can the stitch the 16 image pussle together.

  • THOMAS says:

    Logan, thanks for your comment of a few days ago (30/09/2014 at 17:21) that “You have a point in that Natural Sciences is not Mathematics”.

    I didn’t actually make that point explicitly but apparently you guessed from my previous comments that that is precisely what I think. I also think that this distinction is essential and that it should be underlined.

    The “Natural Sciences” concern the study of the real world AS IT IS and rely 100% on actual observations. It is on the basis of the observations obtained by its study that we can then (and only then) build falsifiable theories. “Mathematics”, on the other hand, is an absolutely essential and totally admirable tool for engineering the means to obtain those observations and then for making the necessary calculations required to formulate a hypothesis which, if confirmed, can then form the basis of a scientific theory. (If that particular theory is ultimately falsified, it’s not a problem: maths will subsequently be equally useful in supporting the alternative, more successful theory).

    But mathematics is (or SHOULD be) only ever a TOOL. It’s no different from any other tool you need, to do the job in hand, exactly like a spade, a screwdriver, a computer or whatever: its importance for the real world, like any other tool you need to do the job, is that it’s a means of doing things accurately, safely and efficiently (just like in everyday life, in fact…). That ranges from “shopping in the supermarket” through “building roads and bridges” up to the extraordinary engineering feat which the Rosetta team has just performed in delivering their probe to Comet 67P/C-G spot on time and in sending back breathtaking and groundbreaking images and data of it.

    And incidentally, maths can also be fun to play around with, as when it is used for playing mind games. Problems arise, however, (as suggested by the number of problems mainstream theory has dealing with the actual observations flooding in) when mathematicians are allowed and even encouraged to believe that the games they play and the resulting intellectual concepts they build (as a child builds a house of cards) actually correspond to the world and the universe we live in. Personally, I have been playing chess (as an amateur) for well over half a century and I have trained children and youngsters with some success. I am hence fully aware of the hypnotic or anesthetic effect the game can exert on people (hypnotic on its adepts, anesthetic on the people who sincerely and rightly admire it as the “king of games”). But the “king of games” is still only a game, just as mathematical mind games are also only games. Neither the rules of chess nor the games mathematicians play have anything to do with real life or the “natural sciences” we use to study it.

    Hats off, again, to the many engineers who have used their incredible mastery of applied maths (incredible for me and probably for nearly everyone else on this blog) to enable Rosetta and (I fervently hope…) Philae, to provide us with an extraordinary hands-on opportunity to study cometary behaviour using both natural science and applied maths techniques …

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