Fine structure in the comet’s jets

In the first OSIRIS image release of 2015, the team provides an unprecedented look at the finer details of 67P/C-G’s dust jets.

Comet 67P/Churyumov-Gerasimenko has shown activity in the form of jets for many months now, but the latest image reveals that the large-scale jets seen in previous images can now be resolved into many smaller jets emerging from the surface, which seem to merge together further away from the comet nucleus. Although much activity still emanates from the ‘neck’ region, jets are also appearing from both of the comet’s two lobes.

 

OSIRIS wide-angle camera image acquired on 22 November 2014 from a distance of 30 km from Comet 67P/C-G. The image resolution is 2.8 m/pixel.  Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

OSIRIS wide-angle camera image acquired on 22 November 2014 from a distance of 30 km from Comet 67P/C-G. The image resolution is 2.8 m/pixel. The vertical line in the bottom right of the image, which seems to separate two regions of the coma with slightly different brightness, is the shadow of the nucleus cast onto the coma.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The image presented here was taken on 22 November 2014 by the OSIRIS wide-angle camera, from a distance of 30 km. It is part of a set of observations dedicated to the investigation of the comet’s general activity. As such, the nucleus is deliberately overexposed in order to reveal faint jets and the collimated nature of the streams of gas and dust rising from the surface.

“This is still the beginning of the activity compared to what we expect to see in summer this year,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “From the last perihelion passage we know that the comet will evolve by a factor of 100 in activity at that time compared to now.”

But the jets are already strong enough now to show distinct features, from which the OSIRIS scientists aim to understand the physical processes that are creating and shaping them.

In this particular study, the jets were observed over one full comet rotation. “By tracking them from image to image, we reconstruct their three-dimensional structures and link them to specific areas on the nucleus, of which the morphology and composition is now being investigated,” explains OSIRIS scientist Jean-Baptiste Vincent from MPS.

By understanding where exactly the jets are emerging, e.g., from the cliffs or plains, the scientists will learn exactly how the activity is generated. The scientists will also learn how the jets interact with the dust particles and gas coma that is surrounding the nucleus, but which is only clearly visible at much greater distances from the comet (for example, take a look at the coma as seen through the ground-based VLT).

In addition to the jets, the new image also reveals surface features from the “dark-side” of the comet. Although this region is not yet illuminated directly – this will happen as the comet moves ever closer to perihelion in August this year – the diffuse light reflected from other areas allows a glimpse of what is to come.

 

 

Comments

80 Comments

  • Andrew R Brown says:

    Thank You Emily,

    What I think has intruiged me more than the jets themselves is the backlit pat of the comet's 'neck' that has been in constant darkness.

    Looks very different to the now very familar front of the neck, with many narrow ridglines.

    Andrew R Brown.

  • Dale Green says:

    Why do the particles move away from the comet? It appears as thought the material is leaving the comet in jets. Recognizing that the sun is heating the comet, why does the comet's gravity not hold onto the material? What forces the material away?
    Thanks.

    • graham says:

      The comets gravity is very low- its a very small body. Escape velocity is only circa 1mt per second (somebody will correct me if I'm too wrong!). Therefore material will be able to escape carried along with the vaporising gases. we don't see the gas - but we do see the dust. And its very fluffy dust - think snowflake rather than sand.

    • Prof Harvey Rutt says:

      The comet's gravity is minute and the escape velocity very low. A very gentle jump would give you escape velocity.
      The dust particles are accelerated by gas, mainly water vapour, ablating from the comet as it warms up. Very quickly as they move away from the comet the gas density falls to very low values, and the dust particle just keeps going. The gas itself is largely invisible. You have to be very careful about any sort of intuitive or 'common sense' interpretation of what you see; conditions on 67P are so radically different to what we are used to.
      Others will doubtless tell you the jets are the result of electrical discharges. The mainstream physics community regards this as utter nonsense.

      • THOMAS says:

        Hi Prof,

        Your recurrent protest that "The mainstream physics community regards this [the jets being the result of electrical discharges] as utter nonsense" is not only unscientific in its formulation, but it is starting to sound increasingly hollow in terms of its substance as ever more contrary evidence is provided by the comet itself to give it the lie.

        The “mainstream physics community” would be much more convincing in its out-of-hand rejection of alternative models which *have true predictive power* if it could provide plausible explanations for observed phenomena which, in its own terms, are utterly unexpected and baffling. Equations which seek to prove that these observations are a physical/mathematical impossibility will no longer do. Abusive expressions such as “utter nonsense” will only still convince the faithful.

        Eventual disclosure of the close-up OSIRIS images of the fine structure of the jets in 3D will conclusively demonstrate that it is certainly not the EU model which is “utter nonsense”.

        • AndreH says:

          Sorry Thomas,

          but as EU cannot it even correctly explain how the Rosetta probe flew to the comet, it is prooven to be greatly wrong already. So it is not worth discussing it. But EU protagonistts typically ignore all evidence that falsifies their theory and jump simply to the next claim if one is prooven wrong. The theory itself is not unscientific, because it can be falsified very easily. It is the behaviour of the protagonists who ignore all the facts which are there to falsify it. As for example that mainstream physicis can calculate the correct trajectory for the probe and bring it to the outer solar system.

          • THOMAS says:

            EU has no issue with the way what we understand about gravity is used to get probes where they are required to be. It's not totally precise (I suggest you google "flyby anomalies" or "Pioneer anomaly") but it works pretty well, with a few inevitable minor adjustments along the way, even if we haven't the faintest clue as to its first causes.

            I was talking about all the other observations (on 67P and elsewhere) for which the standard theory has no plausible explanation.

          • originalJohn says:

            AndreH, You have a completely naive understanding of how spacecraft are navigated and yet you offer it as a falsification of the rational description of the comet as discharging rock body moving through a a plasma current stream. Do you imagine the Rosetta craft, or any other space craft, has the calculated navigation coordinates typed into its system before launch and then everybody sits back for ten years waiting for it to arrive at it destination. That would be a feat. In reality the craft is tracked every minute of every day and any deviation from the planned course is immediately corrected and the course is restored. This is a feedback control system and the Rosetta orbiter has four pairs of delta-v thrusters for this purpose as well as another twenty thruster pairs, and at the start had 1720 kg of hypergolic propellant. Errors in navigation calculations based on the masses of the craft and of solar system bodies would be minute because of the enormous mass differences and easily compensated for in this way. There would be an item included in the mission budget to cover this tracking aspect. I don't know what it is for this one but for the Cassini-Huygens mission it was $57 million dollars.

            Also you see those who understand the solar system as an electrical environment as protagonists. Do you see this as some sort of battle. It is a perfectly reasonable scientific procedure to propose plausible alternative theories, particularly in the case of a theory as fragile as the standard comet theory. And I don't see in this case all attempts at falsification being ignored on the part of the electric description. Have you been reading a different blog. They have all been dealt with. Legitimate criticisms of the standard theory have on the other hand been ignored, such as the very reasonable observation that no ice has been identified on or in the comet nucleus and yet the unshakable faith in sublimating ice as the source of water in the coma continues with confident assertion, and a reluctance to entertain other possibilities.

          • Gerald says:

            Rosetta hasn't been tracked during hybernation and still has been on track within measurement precision.
            Propulsion isn't perfectly accurate, and deviations add up over time, so need to be corrected.
            Most of the propellant is needed for planned acceleration and deacceleration, not for adjustments due to errors in trajectory calculations.

        • martinvolwerk says:

          On the contrary, there is lots and lots of data available from cometary missions and there is no signature whatsoever in the fields data that shows the presence of discharges.

  • Sovereign Slave says:

    This is a truly phenomenal picture! Thanks for posting Emily. We can only hope that the Osiris team is loosening their gorilla grip on “their” pictures.

    Interesting language being attributed to the jets in this article, “fine structure” and “merging” in particular. This strongly implies some kind of organizing dynamic that is arranging the finer jets into larger jets. If the smaller jets were caused by explosive sublimation, by all scientifically valid standards the gas/dust should be dispersing with distance, not merging into larger columnized structures. As the article says, the scientists are now faced with an exciting mystery that they will be studying so they can determine what might be causing this. But based on this article, I believe we can now safely conclude that there is a totally new, previously unknown and unanticipated comet dynamic that is acknowledged to have the power to organize dust into large jet structures within a vacuum. This discovery is obviously outside the standard model, so before ruling anything out, it seems the question becomes, “What are all the known phenomena that could create patterns of organized structure within a vacuum, and can any of them account for these jet structures?” And I get the sneaking suspicion that this time it will stretch all limits of believability to fall back to the common ad hoc explanations of sublimation, supernatural gravity, shock waves, bow shock, or any of the other standby explanations within the standard model theory box.

    • Jacob Nielsen says:

      @Sovereign, consider a number of not perfectly collimated jets, placed in a group and having almost the same orientation. Being not perfectly collimated means: particles leaving in a slightly cone shaped beam. Then at distance 0 you would see the narrow concentrated beams pinpointing each source of jet. Moving away, while not necessarily interacting in any way, the individual beams will seem to merge, optically. Moving even further away, the "merged" or "fused" beam will "dissolve" due to progressively larger distance between particles. No special force or principle at play, just an optical impression.

      • THOMAS says:

        @ Jacob Nielsen.
        In the 16 January press release from the Max Planck Institut für Astronomie, https://www.mps.mpg.de/3879237/PM_2015_01_16_Fine_structure_of_activity_jets, Holger Sierks, PI for the OSIRIS team, explicitly acknowledges the actual *physical reality* of the 'merging jets' phenomenon. He is basing his comments on yet undisclosed 3D images they now have, so there can be absolutely no question of any form of optical illusion. Individual jets really are merging into increasingly larger ones.

        • jacob Nielsen says:

          @THOMAS, this somehow turns into a discussion of the qualities of the words "impression", "phenomenon" and "illusion". I really can't find a substantiation by Holger, of a particular 'merging jet' phenomenon. I see fans or jets or light cones radiating in many directions, seemingly more or less perpendicular to nucleus surface. I see nothing that suggest that the brighter, longer merged jets are anything more than coincidentially 'stacked' from point of view to appear this bright. I don't consider this an 'illusion' in the sense that it somehow obscures its own true nature. I see no trace of interaction between 'rays' (or jets or whatewer) only passive blending.
          The bending of 'rays' must in part be caused by nuvleus rotation and the article does mentions the posibility to study the makeup of the jets on the basis of the 3D structure.
          Btw.: no 'nozzle' required to produce a collimated jet: supersonic speeds suffice.

          • THOMAS says:

            @ jacob Nielsen

            The key words here are quite simply "unite" and "merge". They are used by Holger Sierks himself in his January 16, 2015 press release:

            “Recent OSIRIS images reveal that large scale jets as seen in previous images can now be resolved into many smaller jets emerging from the surface and then *unite further away from the comet nucleus*. [...] From the appearance of individual jets (for instance how *small jets are merged into larger ones*, or how they are bending), the scientists can learn about how the jets interact with the larger dust particles and gas coma, that is surrounding the comet.”

            He is not talking about a simple "impression" or "illusion" but actual MERGING. And he has the 3D images which prove it, we don't.

          • Jacob Nielsen says:

            @THOMAS, yes the keyword is "merge", the way I understand the word: some kind of dissolving of the individual sources into some unity. No demands on forces and interaction? (even if it is often the case)
            By the way: what is the importance of this matter in your view?

    • originalJohn says:

      Absolutely right Sovereign Slave and well said. As you and I know this merging behaviour is standard in plasma current filaments, for one.

    • Ross says:

      This observation flies in the face of conventional theory, given the nozzle explanation as the source of the jet. There is NO reason that the supposed sublimating gasses should be condensing above the comet. They have the mechanism 100% backwards.

    • Richard says:

      Does 67P have a magnetic field?

      • martinvolwerk says:

        probably no internal magnetic field, but we don't know yet for certain.
        there will be a draped magnetic field around the comet building up, which would have its orientation perpendicular to the jets, i.e. mainly parallel to the surface of the nucleus.

  • Phil Stooke says:

    " why does the comet's gravity not hold onto the material? What forces the material away?"

    The comet contains ice (in fact, ices of several different substances, not just water), and the sun's heat makes it 'evaporate' (technically, sublime - turn to gas. That expands into the vacuum of space, and that flow from the surface into the surrounding vacuum is what causes the motion of the dust particles. The exact method of formation of narrow jets is not certain (despite claims for various mechanisms). I have often promoted the idea published about 20 years ago by Jean Crifo and colleagues, in which dusty gas fans are emitted from active area, and where they meet the gas is compressed into a smaller space. If lots of fan-shaped 3D outflows of gas occur, every place where two or three come together will concentrate their dust components into narrow sheets or jets. It might not be the whole story, or fully understood yet, but it's better than assuming the entire edifice of physics is falling down.

  • Gonzalo says:

    Would be nice if the camera could take a fast sequence of images so we could enjoy that jets in time lapse. Their behavior is like a jet? Or more like a flame?

  • IamNotaRobot says:

    What seems to curve some of the jets but not others right after leaving the comet ?

    • THOMAS says:

      @IamNotaRobot

      I would be surprised if the standard "neutral gas dynamics" model had any explanations to offer you. Neutral gas, even expelled under pressure (increasingly hypothetical in the case of the putative sublimation process required by the standard model) would just go "phut" as it dispersed into the no-pressure zone of the vacuum of space. There is nothing in the arsenal of simple standard *thermodynamic processes* to even collimate and merge the jets, let alone curve them.

      The curving you mention is, on the other hand, routinely observed wherever and whenever *electromagnetic* forces are observed acting on *ionized* particles as part of self-organizing electric circuits, starting with what is happening every single second (or rather every nanosecond) on the Sun to produce the extraordinarily high temperature of the Sun’s corona. Here is just one example from an impeccably mainstream-sponsored source showing different degrees of curvature: http://zeus.nascom.nasa.gov/~dmueller/gfx/TRACE171.gif.

      The standard theory misnames the arcs observed on the Sun “magnetic field lines”, presumably in order to avoid having to acknowledge their true electrical nature. (In any case, you just don’t get dynamic magnetic fields without generating electric currents and vice versa). The curved jets observed leaving 67P do not arc back onto the nucleus as we see most of them doing on the Sun. Instead, they are self-organizing to respond to the comet’s rotation and the varying potential at different points of the plasma sheath (aka double layer) which separates the coma and tail from the flow of ionized particles known as the “solar wind”. It would be extremely interesting to observe variations in the curvature or straightness of the jets over a period of time; I understand that is what Sierks and the OSIRIS team are now doing.

      • Adam A says:

        Electrical/electrostatic vs magnetic solar phenomena. Refer to:

        http://thesurfaceofthesun.com/index.html?

        Yes, do these ejecta in fact return to the nucleus having traveled around the magnetic field line under the initial impetus from the sublimation?

        How is the mass balance looking for the comet? Loss rate seems high when considered over geological time - its a wonder it still has any mass left.

        • Gerald says:

          The site, you pointed to, is 19th century level, before fusion has been discovered, and before it was known, that the Sun is billions of years old.

          We know by now, that the Sun is made of hydrogen and helium plus some trace species, see e.g. here:
          http://www.space.com/17170-what-is-the-sun-made-of.html
          Look at the emission spectrum of the Sun, and you see clearly the lines of hydrogen.

      • Gerald says:

        You see the dust, not the gas in the jets. The dust is accelerated mostly by water vapor of sublimating water ice with about the speed of sound, as expected for vapor relaxing into the vacuum. The dust jets are curved due to the solar wind, to form the cometary tail pointing away from the Sun. Add some curvature by the rotation of the comet, if you like.
        Just an easy simplified explanation with standard means.
        Jets, if colliding may interact aerodynamically to unite.
        No need at all for the electric universe stuff, which creates electric charge magically out of nothing, wrapped in rhetoric.

        Regarding the magnetic field lines at the Sun: The hot gas alignes along these field lines; it's not the magnetic field lines themselves.

        • originalJohn says:

          The hot plasma follows the direction of the field Gerald. There are no lines. There is no electric charge "created magically out of nothing" either. Electric currents have been measured in the solar system as I have pointed out to you. Electric current is a flow of charge. Where is the magic there. Can you not grasp the logic.

          • Gerald says:

            It's *because* I can grasp logic very well, I can't follow what you call "logic".
            And, of course, logic taken isolated isn't sufficient; a hypothesis about the physical universe should be consistent with physics and observations.
            I.e., if you suggest an alternative for an established model about nature, it should provide at least an equivalent theoretical framework to be considered.

            These constraints are clearly not fulfilled by the electric universe framework.
            i've thrown away obsolete models many times, and replaced them by improved or better alternatives.
            There exist several competing more or less established theoretical models of physics. But they either are very consitent with observations, or they cover fields which aren't (yet) accessible for experiments.
            It's also well-known, that the two best-established physical theories don't match, i.e. quantum theory and general relativity. So for theoretical physics, replacing quantum theory and general relativity by a better framework covering both domains in a consistent way would be kind of a holy grail.
            Unfortunately the electric universe approach is far from improving the well-known deficits of established physics.

            I've no problem at all with paying attention, that electromagnetic phenomenons are considered where applicable. But whenever other straightforward explanations do the job, they need to be considered as well. Finding out the best-fitting is the job of experiments and measurements.
            Just claiming that "my" personal idea is the best, and ignoring all facts which don't match this idea, doesn't return a useful result.
            As far as I can see, the "established" - although wrong at some point as we know - physical theories work very well with explaining the comet, whereas the electric universe framework has severe flaws.
            Science isn't about selling a given fixed theory, but about finding a better theory.
            The existence of currents doesn't imply that everything is a current. If existence of an object with a given property would imply that all objects have this property, exactly one object would exist in the considered universe.
            If talking about logic, then apply logic, not rhetoric or sophism.
            This implies, after properly defining a theory, to apply the theory quantitavely, and countercheck it with the observations. If there occur inconsitencies, either something went wrong with the observations, or there is a flaw in the theory. Then both needs to be cross-checked until the flaws are identified and the discrepancy is resolved. Otherwise the theory may still be self-consistent, but not applicable to the observation.

            In the case of the comet, sublimating CO2, CO, H2O mixed with silicate dust explains straightforward the observation of ionized CO2, CO, H2O.
            That's as straightforward as water flowing out of a bottle is explained by the bottle filled with water.

            CO2 emission is no way straightforward explained by the interaction of protons with some silicate (Na,K, Fe,Al)nSiO4.

            Solar protons and electrons are easily explained by ionization of neutral hydrogen.

            They are not easily explained by the Sun as a proton source, but not an electron source, with planets or the heliosphere as an electron source, which needs to come from somewhere, together with complications that they don't neutralize when moving in opposite directions, unless there is a strong electric field, which again needs to come from somewhere.

          • Kamal Lodaya says:

            Gerald: I had some discussion with a logician regarding the kind of "physics logic" that was emerging from the discussion on the seeming opposition of the comet's solid-looking surface, with density seemingly well above 1, with its overall density of 0.47. (At one point I was thinking of caves and voids but Consert seems to have convincingly refuted those.)

            Another interesting question is "where are the coma gases coming from?" This seems to be more of an occam's razor argument.

            On the other hand "the comet as toasted pizza" argument (a recent post by Judy) has been challenged by Harvey as relying too much on earthly intuitions.

            What is emerging is a "physics in space logic": something which allows one to keep some physics intuitions and quantitative details in our arguments allowing for their extrapolation into space, at the same time allowing for novel phenomena which we are conjecturing and seeing for the first time.

            One thing I found difficult to reconcile with (in this very academic exercise) is that I was greatly helped by Mattias Malmer's depth-cue-based visualization of the CIVA panorama (I used the picture in an article I wrote on the comet for children). In spite of the fact that there is actually no atmosphere on the comet, imagining how things would look if there were an atmosphere seems to help the mind.

          • Gerald says:

            Kamal Lodaya:
            Thanks, several interesting thoughts! I'll try to reply to some of them, and try to do some elaboration

            Regarding prosity: The CONSERT data constrain the size of the pores, not the porosity itself. So yes large caverns appear less likely / frequent.

            The question "Where do the gases come from?" should be possible to be reduced to the following pattern of logical reasoning:
            B implies A, and
            C implies A, and
            C implies D, and
            D is false, and
            A is true.
            From "C implies D" and "D is false" we get "C is false".
            This leaves "B implies A" as the only possible of the two considered explanations.

            Example:
            Instantiate the logical variables as follows:
            A: "H2O, CO, and CO2 gas is emanated from the comet in amounts high enough to drag Rosetta away from the nucleus."
            B: "Subsurface ices of H2O, CO and CO2 are heated by the Sun."
            C: "Solar wind protons react with water-free rock, including silicates, Assume a possible proton - rock interaction resulting in sputtered water."
            D: "The flux of protons in solar wind is at least double the flux of emanated water molecules."

            In a post below I've esimated the proton flux to 40,000 per cm² and second.
            The comet emits about 1 liter of water per second, that's about 6e23 * 1000 / 18, hence a little more than 3e25 molecules per second.
            The surface of a circumscribed sphere around the comet is about 4 pi r² = 4 pi * (2 km)² = 50 km² = 50 * (100,000 cm)² = 5e11 cm².
            The average emission of water can hence be estimated as about 3e25 / 5e11 = 6e13 molecules per cm² and second.
            This is by a factor 2 * 6e13 / 40,000 = 3e9 higher than the needed minimal proton flux, if all solar protons are converted to water.
            An error of nine orders of magnitude cannot be explained by fluctuations of the solar wind or inaccuracies of the estimates.

            This proves statement D false.

            The above logical pattern applies, and sublimation is the only remaining of the two considered explanations for the emanated gasses.

            Regarding intuition: I appreciate Mattias Malmer's work. His depth-cue visualization inspired me, too, to get an idea about the possible local topography at Philae's final touchdown location.
            Good to see you inspiring young people to get interested in science.
            Finding a good compromise between strict scientific reasoning and Earth-based intuition is an art for itself.

    • PTR says:

      If the jets are dust particles accelerated by the gas "going phut" (which would be the most likely explanation IMHO), the dust 'd keep travelling straight ahead. With the comet rotating that results in curved "jets" coming from the nucleus. The spiral-shaped curvature will then look different depending on the angle from which we see it.
      As there would be a certain degree of dissipation - dust particles travelling not parallel, as they leave the surface in different angles caused by the outgassing - nearby jets may tend to mix or join after some distance.
      To me this seems to perfectly explain what we see here. I'm sure some find a different explanation though 😉

  • graham says:

    I wondered what the process could be too. And we're not the first - there's and interesting paper online - just search for "Formation of jets in Comet 19P/Borrelly by subsurface geysers"

    This paper suggests that to produce a collimated jet it must be moving very fast indeed "supersonic" speeds. The entire paper can be seen here:

    http://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf

    This suggestion also ties in with something said at the AGU meeting where it was said the dust was moving at 700m per second (2520KM per hour!) - unfortunately not all of the presentations are still available and that one in particular I can't find any longer.

    The jets seen on 67P are in greater clarity and resolution than anything possible previously, but they don't look all that dissimilar to those seen on Comet Hartley by the Deep Impact mission. We can expect further papers from the Rosetta team in the future, but surely the evidence is starting to stack up into a strong case?

    • dave says:

      Hi Graham,
      the paper is very interesting,
      It discounts that lifting dust over a wide area by sublimation through a permeable crust.
      This has been suggested on the blog a few times and for the appearance of some of the dust patches.
      It does show how sublimation from a large cavity through a single hole will produce a colimated geyser of gas and dust as long as the ratio between the hole size and and the horizontal area of the cavity is correct, and of course there is enough energy on the surface to give the required amount of heat to conduct through the surface to the cavity.
      They go on to say that there calculations are unlikely to be correct in detail, because of insufficient information on the size and shape of the geyser. For their model they used a cavity with a depth of 1 meter, they expected that these cavities could grow to 3 meters in diameter. This size of cavity should of easily been picked up from the consert measurements on our comet 67p but the data from consert was said to show a homogeneous structure right through the core.
      Even at the end of the paper it cautions on the calculations presented as it was impossible to specify the thermal conductivity, density, specific heat, crustal thickness, ice dust ratio (we have not even detected ice on 67p yet). also they state there are many uncertainties in the physical properties of the cometary surfaces and sub surfaces.

      Its almost as though they have the same problems we do., do we even know what the surface of 67p is yet?

      So although the equations show a possible way forward, we have a long way to go before a method of colimation is understood.

      • Ian says:

        We do know what the surface of 67P is Dave (at least at the lander site) - dust on top of a layer of hard ice.

        • dave says:

          I am afraid that's not true Ian.

          It was stated that under the ice there was a hard surface not inconstant with ice.
          It hardly narrows it down does it, they might just as well said it is hard it could be rock. nether statement tells us anything about the surface except that it is hard.
          So far no ice or even ices have been found on the surface or under it, the article that graham posted above postulates that for the high speed sublimation to work we might expect cavities under the surface a meter deep and 3 meters in diameter. Cavities this big should of shown up on the Consert experiment, but it found no cavities, so even if there was ice below the surface it does not appear to be sublimating.
          Further, esa tells us that the bright patches we see on the surface are not ice.
          If its there Ian it is really well hidden, do you have any suggestions

          • dave says:

            Sorry,

            statement above should say it was stated that under the dust

            Not under the ice

      • Graham Hall says:

        I don't think anything from CONSERT released to date goes into whether cavities of 3 metres have been found or not. Stating that the structure is homogeneous throughout means what it says. The dust examined so far is very fluffy. the gases given off are water, Co, Co2 and the like which sublimate at very low temperatures, which are exceeded now when in sunlight given the comet's proximity to our star. In the AGU presentation it was said in one (that I can't find any longer) that the dust's speed off the comets was circa 700 metres per second. that's in excess of 2500 KM per hour. To me that's supersonic as suggested in the paper.

        Of course the proposition is not proven beyond reasonable doubt, we've not had available the evidence that will be being collected now. But watch this space - the papers will come thick and fast and I'm absolutely confident that nothing will support the EU lobby.

    • logan says:

      Hi Graham. The few of OSIRIS on the wild showed some muddy structures remembering 'primitive British jet engines' 🙂 The Values you are talking about are too damn high :/

      • Graham Hall says:

        Logan

        The paper suggests a collimated jet from a comet requires supersonic speeds for the jet. The AGU was told in a presentation that was at one time available to view but has now been deleted (thank you Max Planck Institute - I hope you never get another public subsidy for your work!) the speed of the jets was put at circa 700m per second - that's supersonic speed (2500Kmh).

        I was surprised too, but given that all the comets that we have pictures of have collimated jets, there is a mechanism to be explained. the mixed comet material is hard when frozen, but composed of gases and very fluffy dust when its not. The density of the comet is low. I don't find it difficult to accept that in the frozen state the mixed cometary material is hard - but that doesn't make it rock as some would have us believe, implying that the Rosetta measurements are completely wrong, despite being able to get the lander after a 7 hour journey to about 100metres of the aim point.

  • Robin Sherman says:

    Thanks Emily. Although a striking image, the resolution is less than that of the regular NAVCAM images and on top of that it has been seriously compressed. Todays NAVCAM mosaic is 1.6MB, this only 178KB. Holger and the OSIRIS team still not giving much away, a sop to alleviate the recent criticism no doubt. Whinging aside, it is an interesting image.

    The collimation process seems to occur on a wide range of scales and as SS says it is intriguing that even far from the surface there is little dispersion. It is difficult to imagine that some sort of electrical/magnetic interaction between the dust particles is not contributing to this. The merging in most cases seems to be due to the different angles the jets are leaving the surface, which in turns seems to be a function of the angle of the surface terrain. Once the less powerful jets cross the path of more powerful jets the dust joins the more powerful flow. There does seem to be very little sign of turbulence though which one might expect.

    Also of note is the way the jets curve, due to the rotation of the comet would seem the obvious explanation. On the far right edge there are two jets that appear to be travelling in the opposite "downward" direction. These two activity points are not that far from Philae's hiding place.

    As Andrew says, the real interest is the tantalising glimpse of the "Dark Side". This terrain appears scoured clean of dust and boulders, ridged and covered in pits and depressions. As previously speculated, erosion of the surface in the Summer, Southern "Hemiduck" is significantly greater than in the North. The pinching at the neck is much less, possibly because the higher solar flux is eroding all areas fairly equally, composition being less critical as all volatiles sublimate, not just some.

  • Ken says:

    From Hubblesite.org: (I know everyone here knows this bit of standard (pre comet CG theory) but it's nice to have a refresher): "There are two types of comet tails: dust and gas ion. A dust tail contains small, solid particles that are about the same size found in cigarette smoke. This tail forms because sunlight pushes on these small particles, gently shoving them away from the comet’s nucleus. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail. A gas ion tail forms when ultraviolet sunlight rips one or more electrons from gas atoms in the coma, making them into ions (a process called ionization). The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower. Both types of tails may extend millions of kilometers into space. As a comet heads away from the Sun, its tail dissipates, its coma disappears, and the matter contained in its nucleus freezes into a rock-like material."

    I would hypothesize that we might be seeing the effects of the ion trail origination as unionized particles aren't going to change courses so fast. For example perhaps in the case of little jet in the middle that bends left and quickly merges with it's bigger neighbor - perhaps the bigger neighbor's net positive charge acts a barrier - helping to funnel the positive'y charged little jet alongside it in the direction of the solar wind.

    • martinvolwerk says:

      why would there be a net positive charge? the electron does not disappear suddenly after a atom has been ionized, it sticks around.

  • logan says:

    The speed of that emitted dust being about ten times the tangential speed of emitting surface? 😉

  • THOMAS says:

    Pity that this truly spectacular image from OSIRIS is actually 8 weeks old but I suppose we must be thankful for small mercies and just wait patiently for the whole treasure trove to be opened, at last, in a few months time.

    The “fine structure” of the jets must now - 2 months later and after all the work done on producing 3D images of them - be crystal clear but nonetheless baffling for the OSIRIS team. It can safely be predicted that the “fine structure” includes spiraling and braided features.

    But what is also remarkable in this image is the large number of what appear as white dots surrounding the nucleus. We can only clearly see the largest but we can make out and further infer a very large number of others, presumably smaller or further away from the OSIRIS camera. Given the scale and the resolution of the image, these objects are certainly not grains of dust: they must be solid bodies and some of them must measure several metres across. It is perhaps time to start attempting to account for the mechanism which is necessarily lifting them from the comet’s surface.

    • THOMAS says:

      (To avoid confusion, I’m not claiming any sort of primacy regarding the surrounding dots/blobs. There was already some discussion about them on the COMETWATCH 20 NOVEMBER thread, initiated by Robin's comment http://blogs.esa.int/rosetta/2014/11/26/cometwatch-20-november-in-the-shadow-of-the-coma/#comment-239062 following Claudia’s suggestion: “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.”
      Many have also been seen on images taken before and since. Again, given the scale and resolution of all these images, they can hardly be “specks of dust or *small* objects”).

      • Ian says:

        The scale and resolution of an astronomical image does not tell you how far an object is away in the image. THOMAS. Those "small white blobs" could be specks of dust a few meters from the instrument or large chunks of ice tens of kilometers away. What you have to do is look at what else the image and science. We see the blobs in comet shadows so they are between Rosetta and the comet. The comet is unlikely to blast large chunks of ice from its surface so the blobs are small. The most likely source is than "of dust or other small objects in the vicinity of the comet".

        • THOMAS says:

          I take your point about perspective, Ian.

          But if you look closely, for example, at the powerful jet shooting up from the top of the head lobe, you will see several less distinct blobs, almost in a line, which are apparently embedded in it. They can hardly be foreground objects.

          I wholeheartedly agree that the blobs cannot be large chunks of ice being blasted off the comet by sublimation: firstly because no ice has ever actually been detected on or below the surface (claims to the contrary being merely based on standard theory assumptions and expectations), and secondly because the putative sublimation process could not possibly be energetic enough to overcome the necessarily considerable inertia of such large, obviously solid objects.

          I suggest rather that these objects are chunks of rock being lifted from the surface by the highly energetic electrical activity which is forming the jets.

          In any case, given their extremely intriguing nature, some of them have presumably already been studied close-up by the OSIRIS team so we shall have conclusive evidence, one way or the other, in a few weeks or months time.

      • Guest says:

        Some clarity is warranted regarding the "blobs" in the 67P image above: Not all the specks of light are comet bits. In fact, most are stars of Cassiopeia. Near the center of the image, 67P is blocking ß Cas (Caph).

        Within a typical position error 230 light specks to stars out of ~300+ light visible specks (including those in the comet's shadowed foreground regions). Roughly 75% of all visible light specs are stars which leaves roughly 1-in-4 specks are comet dust/blobs and/or image artifacts (also a contender). So, although comet ejected comet material is plausible, one has to work to disentangle them from stars first, and then the artifacts second.

        If you want to see a "blink" comparison of the comet image and the associated star field, see my post at http://asterisk.apod.com/viewtopic.php?f=9&t=34418&start=25

  • Nick Moore says:

    The jets are, I expect, emitted through vents similar to geysers on Earth. The vents will direct the particles on similar trajectories. There doesn't have to be ongoing interaction between the particles once they leave the vent in order to maintain a jet.

    That said, jets of material usually fan out gradually, in this case because the particles do not all leave on exactly the same trajectory. Where there are several jets close together, the effect will be for individual jets to merge.

  • I Over E says:

    To the poster above, this is not even tangentially related to the Standard Model of particle physics (note that this is "particle" as in "electrons" and "muons," not dust). The Standard Model is a mathematical formula which has allowed us to identify more than 400 different types of *subatomic* particles. While it may seem counterintuitive, Newtonian and Einsteinian physics are at work here, not Quantum Mechanics or the Standard Model, which apply only to the subatomic.

  • Edward cox says:

    the phenomenal of the jets reminds me a lot of electrical plasma. Could this whole thing simply be caused by electrical potentials as the comet nears the Sun ever deeper into the magnetic heliosphere the electrical differential generating an increase and we see the dust coma as it is pushed off the comet by that differential. Moving At its great speed it's able to generate considerable electric potential on its downward plunge. Also is there any instruments that can measure this activity and any impact the recent solar pole reversal might have had on the field strength?

    • Gerald says:

      Although looking somewhat similar to plasma discharges, the jets are not caused by the magnetic field of the Sun (Lorenz force), nor by an electric potential difference relative to the Sun or to surrounding plasma. But solar wind (which is a plasma overall moving away from the Sun) acts on the gas and dust jets, and bends the jets away from the Sun. Gas is then ionized by collisions with solar wind to form a plasme; this may then be subject to the Lorenz force and spiral along its path.

      The mechanism of dust ejection and outgassing isn't yet described in full detail. The Rosetta mission is designed to find out more.

      But it's very close to sure, that the driving force is mostly sublimation due to heating of volatiles (water ice, carbon dioxide ice (dry ice), might be clathrates (gas bound in water ice), several more chemical compounds) by the Sun. So it's more like steam, smoke and blown dust.

      Impact of solar wind ions onto the surface of the comet may "sputter" some ions, but that's minor relative to sublimation.

      • Gerald says:

        See also Ken's nice summary above.
        (with photo-ionization as a second way to turn steam into a plasma)

      • originalJohn says:

        The Lorentz force is caused by current flow Gerald. It is self induced by the current stream and is the inwardly acting radial magnetic force on any current conductor. In a plasma stream it acts on the naturally formed plasma filaments and is capable of increasing the current density by huge amounts. This feature is exploited in fusion research.
        It is applicable to all current conductors so the solar current plasma is not exempt.

        • Gerald says:

          The point is, such plasma pinches
          http://en.wikipedia.org/wiki/Pinch_(plasma_physics))
          should have been measured by space probes like Ulysses
          http://sci.esa.int/ulysses/

          In fusion experiments you need highly complex technology to provide the necessary geometry

          http://en.wikipedia.org/wiki/Stellarator

          The reasons, why such highly compressed plasma filaments don't form in the heliosphere are the lack of strong electric fields (hence no strong currents), and the missing containment, like a surrounding neutral gas (as for lightnings), or a stellarator (as used for fusion research).

          There are no strong currents, since the Sun provides both, positively charged ions, and electrons. Currents are a statistical phenomenon. So although on a microscopic scale there are strong electric forces between positively cherged ions and electrons of the solar wind, those microscopic fileds (up to maybe a few centimeters) don't act on a larger scale; the annihilate locally.
          Any remaining differences of the electric potential are rapidly reduced by the almost freely floating electrons of the plasma.
          The magnetic field isn't strong enough to cause high voltages, despite moving charged particles.
          High magnetic fields don't come into existence, since there are no strongly electrically charged volumes.

          So, although solar wind plasma could be pinched in a fusion reactor experiment, it doesn't apply, since there is a very different settings.

          • originalJohn says:

            Gerald, I tried a reply here and it did not post so here is another attempt and apologies if it turns out to be a repeat.
            I have not seen any results of heliosphere current measurements from Ulysses so would be grateful if you could post a link. I do know that it spent much of its time above or below the ecliptic plane therefore out of the main current sheet..

            The reasons for the complexity in fusion experiments are the very high energy density required to attain fusion temperature and the need for containment, the objective being fusion under control. The energy densities required for the pinch I have suggested are minute by comparison and no confinement is required in a natural pinch, over and above the self induced magnetic field.

            The potential for the current flow results from the Sun as an anodic element and the heliosphere as a virtual cathode, and all other solar system bodies as secondary cathodes. That potential is there all the time. The filamentary nature of the plasma current generates the magnetic fields which apply the Lorentz forces to the filaments. These filaments coalesce by mutual attraction into larger filaments and the magnetic force persists at a higher intensity and so on. The force is self induced. It is a local effect and may be promoted by particular conditions such as those in the vicinity of comets.
            The Lorentz force applies to any conductor with a current flowing. In solids there is minimal if any increase in current density. In plasma there is no constraint and very large increases are possible, depending on current level.

            As far as I am aware this is a characteristic of plasma that has not been studied at all in astrophysics.

          • Gerald says:

            Here (in NASA's Planetary Data System) you find the calibrated cruise radiation data of the MSL Curiosity rover:
            http://ppi.pds.nasa.gov/search/view/?f=yes&id=pds://PPI/MSL-M-RAD-3-RDR-V1.0/DATA/CRUISE

            Most of the data have been taken clearly outside the magnetotail of the Earth, if you don't trust Ulysses or SOHO.
            You may like to dig into the data to look for anomalies.

            If you don't trust the calibration, here the uncalibrated raw data:
            http://ppi.pds.nasa.gov/search/view/?f=yes&id=pds://PPI/MSL-M-RAD-2-EDR-V1.0/DATA

            From what I've seen sofar, I didn't find indications of punched plasma filaments the way you describe.
            But well, try your luck, maybe you find something interesting.

            Probably your anode - cathode model of the solar system is simply wrong, in the sense of not applicable.

            Electric currents may occur e.g. in the atmosphere of planets, near the surface of stars or in their interior due to the strong magnetic fields, or near the surface of neutron stars with their excessively strong magnetic fields, and their fast rotation.

          • Gerald says:

            Here an overview over the Ulysses mission, showing that it has been out of planetary influence much of the time:

            http://www.swri.org/3pubs/ttoday/fall03/pdfs/solar-wind.pdf

            But when crossing the ecliptic, your "current sheet" should have resulted in peaks of the solar wind.

            Regarding the discharges between the Sun and planets:
            It's hard to study something which doesn't exist.

      • originalJohn says:

        You've misunderstood it Gerald. The Lorentz force in question is nothing to do with the Sun's magnetic field. It is the self induced radial magnetic field generated by each current filament in the solar wind current stream.
        Then you say the solar wind "acts on the gas and dust jets". Could you be more specific about how. A sort of puff is it? Then you say "gas is ionised by collisions with solar wind". Is this the only process you can see, and what do you see as the probability of collision in view of the particle densities involved.

        And whether of not the sputtering of the rock surface is minor or not depends on the impinging proton current density. I have shown that the required current density can be easily achieved by natural processes in the plasma. So sputtering is solidly plausible. Find some ice, even a kilogram or two and the sublimation idea that you favour will immediately grow in plausibility from zero to at least something.

        • Gerald says:

          The solar wind acts on neutral gas by collision (exchange of kinetic energy and momentum), charge exchange (ionization), particularly after ionization by its electromagnetic field ("pickup ions"). I'm attributing this embedded field to the Sun, but it's ok to treat it separately, since it's so much distorted.

          Collision probability seen from a solar wind ion is largely dependent of the gas/dust density and size of the coma.
          Due to the about (order of magnitude, assuming 400 km/s for solar wind, and 400 m/s for gas jets) 1000-fold higher velocity, hence about 1,000,000-fold higher kinetic energy of solar wind ions than sublimating gas from the comet, seen in comet inertial frame, collision of only about a millionth of the gas jets changes the jets significantly.
          Within gas jets gas is dense enough to allow for collisions between molecules within the jet, such that aerodynamic model get applicable.
          You'll get some drag for dust grains within this gas, but also direct collisions of solar wind particles with dust grains, as well as uv photons ionizing dust and gas.
          This additionally allows the electromagnetic field embedded in the solar wind to excert a force on the dust and gas.

          Some of the basics here:
          ftp://space.mit.edu/pub/plasma/publications/jdr_sw_lism/jdr_sw_lism.pdf

          The paper mentions particle densities between 0.1 and 135 ions per cm³.
          For a densely-packed one-molecule layer of gas (by projecting the neutral gas volume into a 2-dimansional plane perpendicular to the velocity vector of the solar wind) the collision probability is 1, meaning collision is certain.
          To get a collision probability of a solar wind ion with randomly distributed neutral gas moleules of 0.3, a 1-molecule layer is still sufficient. With each random layer impact probability converges rapidly towards 1.

          This means, that a substantial part of the momentum, charge, and energy of the solar wind is exchanged even with a very dilute gas.

          The other way round:
          Take the hydrogen atom as a lower bound for the cross section of a proton, when interacting with molecules. We get about 1e-16 cm². Take average solar wind with 5 protons per cm³, and a velocity of 400 m/s, hence a flux of 40,000 protons per second and cm².
          This means, we get about 1e-16 cm² x 40,000 /(cm² s) = 4e-12 collisions per second for a given molecule of the neutral gas. As shown before, a jet is disturbed significantly by interaction with 1e-6 of the molecules with solar protons.
          So divide the 4e.12 by 1e-6 to get 4e-6 direct hits per second for 1 million neutral molecules, or one hit every 69.4 hours to accelerate the coma purely by collisions on a Newton mechanical basis.
          For CMEs the time reduces to about a tenth, or 7 hours, enough to separate part of the cometary tail from the comet.

          Now add the ionization by these collisions and the electric field of the solar wind, and you get shorter times for pickup ions.

          Remeber, that the hydrogen ionization energy is higher than the ionization energy of the outermost electron of most atoms, including oxygen, such that the cross-section of the proton has been chosen very conservative, meaning it's larger for most collisions with molecules.
          Adding consideration of electrostatic interaction with molecules below the ionization energy extends the cross section of the proton further.
          Energy release due to charge exchange adds energy to the collisions beyond the mere mechanical portion.
          As an order of magnitude estimate, the ionization energy of hydrogen is about 13.6 eV (http://en.wikipedia.org/wiki/Rydberg_constant).
          Part of this energy is released during charge exchange and transfered into the degrees of freedom of the colliding particles, three of these degrees of freedom are translational; for the possibly resulting atomic hydrogen, as an example, these translational components are the only degrees of freedom. That way another several km/s velocity can be added; by m=E/c², and E = mv²/2, a proton mass of about 926 MeV/c², you'd get about v = sqrt(2 x 13.6 eV / 928e6 eV) x 3e5 km/s = 51 km/s, if all engergy of the electron capture would do go the newly formed hydrogen atom.

          • Gerald says:

            ... if all energy of the electron capture would go to the newly formed hydrogen atom, if it would have been at rest before.

          • originalJohn says:

            Thank you Gerald for your detailed and considered reply about the collisions aspect. Interesting observation that the kinetic energy of the solar wind protons is a million times greater than the gas. This of course also emphasis the the work that the protons can do when they strike the comet nucleus. As you say collision probability and therefore ionisation probability depends on the density of the jets. To my knowledge we do not have a published figure for this yet. Neither do we have a figure for the change in density moving away from the point of emission on the comet surface. And neither do we have more than one result ( I recall for the neutral CO2/ H2O ratio, and that for an indeterminate position in the coma, not in the jet) for the composition of the jets. So we don't know for example the ratio of ions to neutral matter at any point. The jets are clearly more dense near the nucleus but must disperse rapidly into the low pressure vacuum surroundings such that the gas pressure would be very low and therefore separation between molecules would be very great. We don't have a figure for this either. It does emphasise though that the collision model would be very different in the coma and the jets and that the situation is very complex. The ideal densely packed molecule layer, and consequent probability of 1 would not therefore persist for very long.
            I have a lot of issues with the Richardson paper but a detailed criticism here would take far too long. I will briefly summarise and say it is not reasonable to call it the basics. It contains a number of contentious interpretations not least the description of field lines as a physical entity, which they are not. Also the confusion in cause and effect between current flow and magnetic field, and statements like "magnetic field cannot pass through a conductor" and the implication that magnetic fields can somehow act independently of their causal influence, the flow of electric current. His paper is thus a subjective interpretation which does not consider any alternative interpretation and whilst it contains some interesting data it has no justification to be accepted as definitive and incontrovertible. I guessed it dates from around 2010 and even since then it has been superseded by NASA confirmations, such as the lack of a "bow shock" at the heliosphere boundary.
            I accept all you suggest about the relative size of the proton and likely frequency of collision with gas molecules. But should you not have said 4. e-6 hits per second for 1 in a million neutral molecules.
            Also I follow your suggestion that the resultant energy and thus speed of hydrogen atoms would be increased by somewhat more than an exchange of kinetic energy, I would however appreciate a brief explanation of the concept of degrees of freedom of colliding particles.

          • Gerald says:

            I agree, that the precise numbers about gas density near the comet aren't published, so we can just do some very tentative estimates at the moment.
            I've referenced the paper mainly to provide density estimates of the solar wind.
            About degrees of freedom: In the considered context that's a notion referring to quantum mechanical properties of gas molecules.
            Protons and hydrogen atoms are sphere symmetrical and small. Therefore they have no vibrational and no rotational degrees of freedom at "low" temperatures.
            Some background here in Wikipedia:
            http://en.wikipedia.org/wiki/Degrees_of_freedom_(physics_and_chemistry)#Degrees_of_freedom_of_gas_molecules

            You may think of the degrees of freedom of atoms and molecules as the means kinetic temperature is stored on the atomic level.

          • Gerald says:

            Regarding the composition of the sublimated gas, not specifically the jets:
            http://blogs.esa.int/rosetta/2015/01/22/comets-coma-composition-varies-significantly-over-time/

        • Gerald says:

          The plausibility for sublimation is very high, since water, carbon monoxide and carbon dioxide is measured. Where else should it come from?

          Whenever there comes steam out of a pot, it's highly plausible, that it comes from a liquid inside the pot, usually not from self-induced electric current, sputtering the outside of the pot. The pot can well be dry at the outside.
          It's your task to provide evidence for your fringe electric universe hypothesis, which has been ruled out many times.

          • originalJohn says:

            The kettle analogy is invalid Gerald. Nobody would or has ever suggested that the plume of steam might result from an electric discharge. There is no reason too.
            On the other hand there is every reason to suspect that there might be a better explanation for how comets work than the fragile sublimation idea. ( as there would be for the steam if there was no water in the kettle and the kettle looked more like an egg whisk than a kettle).
            The reason electric discharge is a good alternative is that the behaviour manifests recognisable characteristics of electrical effects and we know that the comet is moving in the solar electric field.
            I should also point out Gerald that the only people who can test that hypothesis and provide evidence for or against it at this time are the ESA. Whoever else proposes that or any other hypothesis can do no more than speculate.
            The electric hypothesis has been contested on this blog but not ruled out. And before the discussions that have taken place here it has not been considered at all.

          • Gerald says:

            The sublimation "idea" is already definitively evidenced.
            As 67P/C-G gets more active, I'm sure we'll get even more evidence by exposed and ejected rock/dust/ice mix.

            But a deep dogmatic belief in plasma discharges may still ignore all facts, call ice "plasma glow", and claim electric universe models confirmed.

            So, what level of confidence is needed to convince electric universe proponents of actual physics?

        • Gerald says:

          A "current density" able to sputter the comet would have sputtered Rosetta, too.
          By simplest logic there can't be a proton flux as high as you suggest: Rosetta and other probes would have turned into a comet and vanished.

        • Gerald says:

          Regarding the ice: It's mixed with dust and rocks, and mostly covered by dried rock and dust - yet.
          But not everywhere. First icy rock samples are going to be exposed:
          http://www.esa.int/spaceinimages/Images/2015/01/Icy_alcoves

  • Bill Harris says:

    Here are two beautiful renditions of the OSIRIS image of 22 NOV 14. This image had the basic exposure adjusted to show the faint parts of the dust jets and coma, while overexposing the body of the comet.

    This first image has been processed to show fine details of the North Polar Dust Jets:

    http://univ.smugmug.com/Rosetta-Philae-Mission/Rosetta-Dust-Jets/i-z4KvnxD/0/L/ESA_Rosetta_OSIRISwac_20141122--enh1-L.png

    The second image has been processed to show details of shadow of the comet on the inner coma, the faint outer details of the North Polar Dust Jets and the "winter" dark side of the comet illuminated by reflected light from the comet along with a silhouette on the lower side.

    http://univ.smugmug.com/Rosetta-Philae-Mission/Rosetta-Dust-Jets/i-dh44ZZq/0/L/ESA_Rosetta_OSIRISwac_20141122--enh4-L.png

    The weakly-illuminated dark side may very well be lighter in tone ("higher albedo") than the sunlit-side of the comet at this time. Remember that this unlit side of the comet has been in the cold of outer space for years and may well be within a few tens of degrees of Absolute Zero. And with the gas-rich environment of the coma due to sublimation processes on the sunlight side, this cold dark side is a ideal "cold trap" and may be covered with an exotic frost of gases, organics and ice. Once the dark "winter" side of the comet is exposed to sunlight in it's "Spring" later this year, we may see spectacular sublimation of this fresh surface material.

    Just Arm-Waving. 🙂

    --Bill

  • THOMAS says:

    In a January 16, 2015 press release (https://www.mps.mpg.de/3879237/PM_2015_01_16_Fine_structure_of_activity_jets), the news and its possible repercussions and predictive power comes “straight from the horse’s mouth”…! Holger Sierks (OSIRIS Principal Investigator employed by the Max Planck Institut für Astronomie) states that “Recent OSIRIS images reveal that large scale jets as seen in previous images can now be resolved into many smaller jets emerging from the surface and then unite further away from the comet nucleus”. (By “recent”, he apparently means the above 8-week-old November 22 image…). He adds: “From the appearance of individual jets (for instance how small jets are merged into larger ones, or how they are bending), the scientists can learn about how the jets interact with the larger dust particles and gas coma, that is surrounding the comet.”

    To me, it sounds very much like braided hair, with the individual strands which emerge from the head being wound into fine tresses and then into plaits to ultimately form full-blown ropes of hair. (In this connection, it should perhaps be pointed out that the ancient Greek word “κόμη » (kómē) means “hair” and the derived Latin word “coma” means “hair of the head”: see http://en.wiktionary.org/wiki/coma).

    We can be confident that the jetting phenomena observed (now reportedly resolved in 3D) will be found to demonstrate the self-organizing properties of the comet’s electrical activity, as the spiraling Birkland currents feed the coma (and then the tail) with solid particles of varying calibre and a variety of mainly ionized molecules.

    Random “outgassing” into a vacuum can in no way lead to the unification of individual puffs of sublimating water-ice with entrained dust into the majestic collimated columns we see in this image.

  • logan says:

    Want to pinpoint to those perfectly aligned and regularly separated boulders at the top of the body. 4 total. [Like jet pits in a carrier 😉 ]

    • daposter says:

      awesome....
      there are other weird coincidences too:
      those 'craters' (which could also be things analog to sprung bubbles in mud, all in slomo... I am not implying there is mud on the comet....) seem sometimes to appear in pairs, rows of pairs...... go figure...

    • Robin Sherman says:

      Bill's second image above makes those "studs", their strangely regular spacing and size very clear. What it means is anyones guess. Markers for different layers during the accretion process, result of a string of impacts like Shoemaker Levy 9 on Jupiter, coincidence, signs of internal structure, no idea.

      Back to the "curving" jets. At the AGU meeting, I think it was Katherin Altwegg said that due to the activity and density of the extended coma that the Solar Wind could not gat any where near the comet nucleus. The bow shock that gave rise to the famous singing comet also creates a magnetic field far in front of the comet preventing the Solar Wind from reaching the comet. It is the shape of this shock wave and magnetic field as it travels past and around the comet that I understood to be what creates the initial shape of the tails, that is narrowly confined, and then as the dust, gas and ions emerge from the shadow and bow wave wake, the solar radiation and Solar wind separate the dust/gas from the ionised particles to give the two distinct tails. This shock wave front and it's shape are also expected to be present on Pluto and New Horizons is specifically going to look at the plasma and magnetic fields to see if Pluto also has a "comet tail". Similarly MAVEN is doing the same thing at Mars and the instruments on Rosetta too. Unfortunately these teams were conspicuous by their secretiveness at the recent AGU meeting, so there may be results clarifying the initial findings outlined on this blog several months ago. It would seem unlikely that this close to the nucleus the bending of the jets is due to the Solar Wind, but more to do with the interaction with the material of the inner coma, the motion of 67P, or both.

      • Robin Sherman says:

        I should add that the shape of the coma itself and the shock wave in front of it, is in large part due to the Solar Wind, the Sun's magnetic field and solar radiation so I suppose there is an indirect link to the Solar Wind.

      • Gerald says:

        This would really be interesting to know, how far the solar wind can survive the coma.
        Particularly since MAVEN seems to have found protons much lower in the Martian atmosphere than expected, probably due to temporary recombination to neutral atoms, and stripping of the electron deeper in the atmosphere.
        Protons seem also to be implanted on the Martian surface in the top few microns.
        Great opportunity to get a better understanding with Rosetta / Philae.

  • logan says:

    Ducky in a sharp an interrogative look at us, eclipsing his own dust-o-sphere at bottom. Misty, blended and enveloping.

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