CometWatch 22 August

Today's CometWatch entry, featuring a dramatic outburst from Comet 67P/Churyumov-Gerasimenko, was taken by Rosetta’s NAVCAM on 22 August 2015, about 336 km from the nucleus.

ESA_Rosetta_NavCam_20150822_LR

NAVCAM image of Comet 67P/C-G taken on 22 August 2015, nine days after perihelion. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The image scale is 28.6 m/pixel and the image measures 29.3 km across. Although the activity is extraordinarily bright even in the original (below), the image above has been lightly enhanced to give a better view of the outline of the nucleus in the lower part of the image, as well as to show the full extent of the activity.

In this view, the comet is oriented with the large lobe up, revealing the Imhotep region as well as parts of Ash to the left, Aten at the centre (close to the edge and partly in shade), and Khepry to the right. The outburst seems to originate from a patch of the comet's surface between Imhotep and Khepry.

The smaller lobe can be seen in the lower right part of the image, where indications of the ongoing activity over much of the comet can also be seen.

Comet 67P/C-G made its closest approach to the Sun, or perihelion, on 13 August 2015, just nine days before this image was taken. Based on observations made during previous passages of the comet through the inner solar system, scientists expect the activity to remain high for several weeks after perihelion, and the comet is likely to produce more of these sudden outbursts and peaks of activity.

The science instruments on Rosetta have also observed these outbursts and the teams are busy analysing the data to understand the nature of these events. These in-situ measurements are being complemented by astronomical observations from ground-based and near-Earth telescopes to try and understand the global impact of these events on the much larger coma of 67P/C-G.

The original 1024 x 1024 image of today's CometWatch is provided below:

ESA_Rosetta_NavCam_20150822

Comments

69 Comments

  • Marcin says:

    That's quite close to the Philae location, isn't it? Shame that we don't have any contact with the little lander, photographs might have been amazing.

    • Tom Billings says:

      No, the Agilkia landing site was on the smaller lobe of the comet. This eruption of gas and dust is on the larger lobe.

    • Kastior says:

      Marcin, I think Philae is on the other lobe of the comet, the small one. 🙂

    • Ramcomet says:

      Marcin,
      Actually, Philae is on the opposite end, on the "head". Here, you are looking at the bottom of the "body" of the duck.
      It certainly is a shame that they probably can't contact Philae till after everything subsides and Rosetta can move back in close again, if even then.
      I wonder if at least some commands got through to keep taking pictures, even if Philae cannot reply?
      Still... much more to come!

    • Kamal says:

      Marcin: No, the action is in Anhur or Khepry on the bigger lobe which is far from Philae. I find it hard to make out but the 12 August flash was also close to Anhur or Khepry.

    • Gerald says:

      Philae is sitting on the smaller lobe. The above outburst occured on the larger lobe.
      Would have been amazing, nevertheless.

  • ianw16 says:

    "The science instruments on Rosetta have also observed these outbursts and the teams are busy analysing the data to understand the nature of these events. These in-situ measurements are being complemented by astronomical observations from ground-based and near-Earth telescopes to try and understand the global impact of these events on the much larger coma of 67P/C-G."

    Good to hear. Is it prediction time yet 😉
    I'll go with these outbursts being mainly driven by CO/ CO2. No anomalous temperature data will be seen. No spike in magnetic data will be seen. There will be a slight increase in soft X-ray/ EUV due to additional charge exchange with the solar wind, but nothing dramatic. If the probe is close enough, we may see further extension of the diamagnetic cavity.
    Not exactly going out on a limb, I know, but that is what has been seen at other comets, so not expecting this one to be dramatically different.

    • THOMAS says:

      @ianw16
      "...that is what has been seen at other comets, so not expecting this one to be dramatically different."

      You mean "that is what has been seen at other comets" during hour-long flybys? Sure, maybe so. But so what? If we'd stuck around for over a whole year as we have at 67P, we would certainly have seen a number of far more impressive events than this one, with the attendant intense plasma activity and high temperatures which they entail. Your "expectation" is like stating that it can't possibly ever rain in Manchester on the basis of a one-day trip there during a heat-wave. 67P is showing us NEW types of cometary behaviour in close-up which cannot possibly be accounted for by referring back to the scant data acquired during those fleeting flybys of other comets. That’s why we went to 67P.

      • Marco says:

        Hi Thomas,

        You are ignoring the fact that this is necessarily a long exposure time to get any surface detail whatsoever. Thus the "intrinsic brightness" is not intrinsic at all. It is just a huge amount of gas and dust expelled omnidirectionally from a small area of the surface. It is highly reflective compared to the surface, thus saturating the pixels at the long exposure time even with unstretched lighting. This is simple optics, and then simple physics to work out what we are seeing. As to the cause, we shall get more clues as to the surface changes or lack thereof when we look closer again.

        • THOMAS says:

          Hi Marco,

          I don't call a 1.5-km-diameter circle a "small area of the surface"... It's huge! - hundreds or thousands of times larger than any of the other activity-emitting areas so far observed (including the recent July 29 “jet”). And that lopsided dome of matter protruding half a km up above the rim of the larger lobe is of the same dazzling white as that huge surface area which is producing it. It's certainly not all reflected sunlight, by any stretch of the evidence.

          Be that as it may, we're truly in money time here and it's the simplest of all parameters - temperature - which will decide the issue: if EU theory is correct, then this gigantic flash is the result of a massive arc-mode electric discharge of apparently unknown duration and the temperature recorded in the area at the time must necessarily be extremely high. If, on the other hand, the VIRTIS data for this event shows *reduced* temperatures all over the base of the outburst and inside the dome of rising matter (as the physics of sublimation would require), then I personally would consider the EU theory to be falsified and some form of sublimating ice model to be confirmed. I for one eagerly await disclosure of this essential VIRTIS data.

        • Marco says:

          Hi Thomas,
          I think this has to be analysed methodically and objectively. First of all, this phenomenon is on the daylight side of the comet, so the bright areas are also subject to sunlight. There are lines radiating from the bright zone - following them back to the origin I would say the origin is much smaller than 1.5 km. the area of saturated pixels is also roughly circular, adding weight to the possibility of gas and dust expansion omnidirectionally from a small area, and making your suggestion that it is a large intrinsically bright surface event somewhat fanciful. The lopsided "dome of matter" is not matter at all but just the back of the almost circular bright area. No-one has any reason to hide the temperature or lie about what the VIRTIS readings are, and there is really no need to publicise them unless they are spectacularly unexpected in terms that the experts weigh these things up. Standard cometary thinking has no particular prediction on whether the VIRTIS measurement is higher or lower than the average surface temperature of the moment despite your claim. You haven't mentioned a particular threshold temperature or what temperature your guess would be assuming you expect it to be very high. I suggest that the temperature, whatever it is, is of interest, but meaningless unless there is predictions in numerical form done in advance of the official publication of the temperature, and neither the mission scientists nor supporters of any theory (including stretch theory, EU, and panspermia) have made a numerical prediction on temperatures of any phenomena. eg. Temperatures between 300K to 350K are to be expected on such outbursts.

          • THOMAS says:

            Hi Marco,

            You write “I think this has to be analysed methodically and objectively.” I totally agree, of course, but I would add that, in addition and above all, the analysis must be based, as an absolute prerequisite, on objective and correctly interpreted OBSERVATIONAL EVIDENCE.

            In this connection, I take issue with your description of what is before our eyes and I maintain my own description, which it is apparently necessary to detail more fully and precisely:

            Firstly, the area of saturated pixels on the surface of the comet nucleus is indeed “roughly circular” (even though it of course appears oval to us since we are observing it from an angle of elevation of probably about 30°) and I see no reason to doubt that the diameter of this white disk on the comet surface is roughly 1.5 km: if you blow the picture up, you will see that there is a perfectly sharp demarcation between the pure white of the disc and the surrounding rough terrain of the top of the head lobe. It’s as if a disc of white paper were lying on a flat, uneven dark-grey rock. There is nothing “fanciful” about this: this intrinsically bright surface area is what is objectively before our eyes – it cannot be an artifact produced by “gas and dust [expanding] omnidirectionally from a small area” as you claim, because of the totally distinct nature of the demarcation separating the white area from the surrounding grey rock.

            Secondly, what I called the “lopsided dome (slanting up to the right) of dazzling white material” can in no way be “just the back of the almost circular bright area”, as you claim. If you observe the far rim of the head lobe clearly visible to the left and right of the bright patch, it is perfectly obvious that there is a body of something which just as blindingly white as the circular surface disk PROTRUDING UPWARDS from the surface for a distance of approximately 0.5 km – it is obviously not simply the continuation of the far rim of the head-lobe, as you seem to be claiming. In other words, you are apparently wrongly seeing this white area as a single 2D entity whereas it is clearly as three dimensional as the rest of the comet nucleus, with two distinct entities: the 1.5 km-diameter white surface disc + the 0.5 km-high white emanation which is being projected upwards from it (as if a deep, white, lopsided, round-bottomed porcelain bowl had been placed upside down on our disc of white paper lying on our flattish grey rock…). Here too, in the blown-up picture, there is a perfectly distinct demarcation between the upper boundary of the white emanation and the illuminated lines radiating away from it (together with the white lines radiating from the very edges, left and right, of the 1.5 km-diameter white surface disc). The only thing to slightly attenuate the sharpness of this demarcation (in the blown-up image) is a complete array of relatively short, thin, spike-like jets, like flames, radiating upwards from the white dome-like entity (and which are totally distinct from the large-scale radiating lines of light).

            The complex, clearly-visible reality of this event, once described in detail, can thus hardly be accounted for simply by sunlight reflecting off supposedly omnidirectionally entrained dust. (Moreover, I note that everyone on the blog is apparently happy to describe this event as a “flash”, a term which is clearly and rightly more evocative of lightning bolts than of sublimating ice or reflective dust…).

            As for temperature, the EU model as I understand it makes no bones about predicting temperatures inside the surface disk and the white emanation (plasma) which rise high into the thousands of K. Is that good enough for you as a prediction? Such data has not yet been published yet, for sure, but the Rosetta teams were reported to be very busy working to try to understand the science data connected with this event, strongly suggesting that, on the face of it, they don’t understand it. If such temperatures have indeed been observed, it is perhaps understandable that the information has not yet been published “just like that”: the inevitable implications would be as much of a “game-changer” and a paradigm-shifter for the whole of the astronomical community as were the observations of Jupiter’s moons by Galileo which led to the established geocentric vision of the solar system (and the universe) being replaced by a more correct heliocentric vision.

          • THOMAS says:

            Marco, you write “Standard cometary thinking has no particular prediction on whether the VIRTIS measurement is higher or lower than the average surface temperature of the moment despite your claim.”

            Marco, what you call “standard cometary thinking” is only “thinking” and what the proponents of the standard “dirty iceball” comet theory had “thought” before Rosetta arrived at the comet has been confounded on almost every possible count, by both the images and by much of the data (cf. Holger Sierk’s “expect the unexpected” and Matt Taylor’s “game-changer” pronouncements).

            It would hence be more scientific to speak rather of the *laws of physics*, one of which requires that any phase-change of matter necessary entails a significant, and thus detectable, temperature rise or fall compared with the initial state. In the case of sublimation (solid>>>gas), it so happens that the temperature necessarily DROPS sharply! So ANY findings showing a temperature INCREASE in this area, however slight, would pose further huge problems for the “sublimating ice” model. And any SIGNIFICANT increase in temperature (even above a few tens of degrees) would utterly falsify the theory, in simple application of correct scientific method, on the basis of the application of the known laws of physics. As I have stated, the EU model requires the observed temperature to be up in the THOUSANDS of K and I predict that this will prove to be the case if the relevant instruments on board Rosetta were designed to record such extremely high temperatures.

          • Marco says:

            Hi Thomas,
            I am convinced that a measurement of 1000 K plus is also fanciful, but I am glad you made a specific prediction which at least makes the claim of an electric arc mode flash or whatever you are claiming it to be, falsifiable. A stored pressure outburst or a BLEVE liquid phase explosion event would have quite a dynamic temperature through the event, but nowhere near the temperatures you are talking about, certainly on or near the surface.
            I have no trouble believing that the saturated pixels are from reflected light, and the "demarcation line" is just a "bubble" of expanding gas and dust emanated from the same point as the lines are radiating from. A video would show this more obviously, but I am quite satisfied with an expanding dust and gas situation from a small area.

          • THOMAS says:

            Hi Marco,

            You wrote in an earlier post that “this is necessarily a long exposure time to get any surface detail whatsoever”, to try to justify the saturation of the pixels merely by the alleged reflection of sunlight off dust particles. A long exposure time is indeed *required* by your theory but as far as I know, we have been given no actual information on the subject. You are simply inferring the exposure length to make your theory possible.

            The same “necessarily long exposure time” poses a huge problem, however, for your more recent idea that “the demarcation line is just a bubble of expanding gas and dust emanated from the same point as the lines are radiating from.” The most conservative estimates put the velocity of the matter being transported inside the jets at 10 m/sec, and that was just for relatively weak jets compared to this explosion. I remember other official estimates speaking of 700 m/sec for some jets…. So how does even the most conservative velocity estimate square with the absolute sharpness of the demarcation lines (of both the 1.5 km diameter saturated surface area and the 0.5 Km high saturated emanation) if the image was indeed acquired after a “necessarily long exposure time”? The problem becomes even more insoluble if considerably higher velocities are considered, as seems perfectly legitimate given the obvious violence of the event.

            With the “electric” interpretation on the other hand, the sharp delineation of the reaction zone (comet surface and emanation) is actually *expected* and the velocity of ejected material is irrelevant, since the event is interpreted as being an electric discharge in arc mode, as with a welding arc (see, for example, this arc-welding picture: http://photo.machinestogo.net/main.php?g2_view=core.DownloadItem&g2_itemId=138&g2_serialNumber=4): the precise extent of both the blinding white surface area and resulting “ball-of-fire”-like emanation (actually white-hot plasma of undetermined composition)remains constant since its boundaries are rigorously and simply determined by the strength of the current applied – the of exposure time is totally irrelevant, it can be either a second or ten minutes. (Note also, in the photo of the arc-welder in action, how the ejected materials – the white lines – are quite naturally ejected omnidirectionally…)

            As for a temperature of 1000K being “fanciful”, what you presumably mean is that in your eyes, the *electric discharge* theory is “fanciful” quite simply since you don’t believe in it. For my part, a temperature of 1000K is logically impossible in any scenario: In the arc-discharge scenario, the temperature must logically be far higher (a welding arc is around 6000K, I believe…) with copious X-ray and UV emissions, while the phase-change scenario (sublimating ice or your preferred BLEVE) necessarily entails considerably lower temperatures than the average surface temperature of the comet, by application of the known, basic, laws of physics. I suspect that the concomitant science data which the Rosetta teams are busy working to try and understand is utterly incomprehensible for them because the recorded temperatures and spectra are very far from being consistent with the standard model.

          • Gerald says:

            THOMAS: "...*laws of physics*, one of which requires that any phase-change of matter necessary entails a significant, and thus detectable, temperature rise or fall compared with the initial state..."

            No, melting ice under "normal" conditions has 0°C like the fresh melt water.
            At the triple point of water there exist three phases (ice, liquid water, steam) the same temperature and pressure.

    • Kamal says:

      Thomas: But if one went to several hundred places throughout the UK for brief trips over several decades and never found any rain (I find that difficult to imagine!), one might make some conclusions.

      • THOMAS says:

        Sorry, Kamal, I don't follow you. Which conclusions, based on what logic?

  • Sovereign Slave says:

    "the teams are busy analysing the data to understand the nature of these events."

    Uh, I guess so. Is it just me, or does that "extraordinarily bright" light also seem extraordinarily large?

    Now, I know electricity can generate extraordinarily bright light. How does sublimation do it?

    • Ramcomet says:

      No electricity required. Large area intense brightness can be explained as a photographic artifact. The intense source "glow" area, even if nothing but explosive dust, is easy to understand. Dust/ice crystals (CO2, etc.) reflective properties will utterly "burn", or overexpose the camera's "f-stop" setting, which was set fairly wide open, so to speak, on "charcoal setting" , to see detail on 67P.

      I for one would really like to see darker exposures if available, to see more structure at the source!

      • Sovereign Slave says:

        @ Ramcomet
        Photographic artifact? Possible, but the article doesn't elude to this. What it does say is that "the activity is extraordinarily bright even in the original" photo. The word extraordinarily begs a lot of questions. Article also says the scientists are seeking to understand the nature of these events based on the data, which implies that they do not currently understand it. So it seems presumptuous for others to claim they do understand it based on pat answers to yet more mysteries. The frustration is that there is no quantitative information revealed about the exact intensity of the light so that it can be compared to what could be normally expected from reflected light bouncing off of sublimated material. Seems they would have this information and easily reveal that its ordinary reflected light (as opposed to extraordinary), but for some reason they haven't done this.

        • THOMAS says:

          Above all, they necessarily have the temperature data from the huge surface area at the base of the explosion and from the brilliant white matter making up the lopsided dome jutting up above this area. That simple temperature data is a sure-fire indicator of the presence or absence of electric discharge activity and has thus already settled the sublimation versus electric discharge debate once and for all: EU theory requires temperatures in the area to be extremely hot since it interprets this phenomenon as a massive arc-mode electric discharge, whereas the standard sublimation theory requires *reduced* temperatures.

          • Harvey says:

            The assertion that sublimation necessarily causes reduced temperatures is incorrect.
            It is true of a thermally isolated sample, which must supply the heat of sublimation from internal energy and so cools. This reduces the vapour pressure and so sublimation and further cooling are reduced.
            However *with an external heat source* namely in this case the sun, that can supply the latent heat sublimation does not necessarily imply cooling. Indeed it's perfectly possibly for the temperature to *rise* slightly in such circumstances, accompanied in turn by increased sublimation, until an equilibrium is reached between thermal input and sublimation rate removing latent heat.

      • THOMAS says:

        @ Ramcomet

        "The intense source "glow" area, even if nothing but explosive dust, is easy to understand. Dust/ice crystals (CO2, etc.) reflective properties will utterly "burn", or overexpose the camera's "f-stop" setting..."

        To help us to understand the nature of the exotic physical processes you are enlisting here, could you please explain 1) what “explosive dust” is, and 2) how CO2 “ice-crystals” come to be present above the surface of the dazzling white 1.5 km-diameter circular “patch” which is clearly the source of this event. In any case, this shining beacon is obviously far too bright for it to be simply sunlight being reflected off any sort of solid particles.

        • Gerald says:

          THOMAS, you're neglecting the just about 5% albedo (pitchblack) of the "normal" surface of the comet.
          Ice or just dust particles scattering the sunlight can easily look much brighter.
          Nothing fundamentally mysterious.
          At least not for "standard" physics.

          Interesting nevertheless the details leading to the outburst, and the detailed composition of the ejected material.

          • Marco says:

            Gerald,
            Would you consider the possibility of a BLEVE explosion triggered by a surface breach (the surface breach caused by expansion and contraction of the surface crust which was sealing the pressure)
            I know you are thinking supervolatiles in a subsurface pressurised cavern similarly breached, but I have listed numerous (ok vague) elements of evidence for subsurface liquids (necessarily below the surface with a pressure seal which is necessary anyway for this kind of outburst)

          • Gerald says:

            Hi Marco, I woudn't entirely rule out a minor contribution by a BLEVE, since some liquids might condense in a pressurized environment. In this case the liquids would exist as microscopic films on dust and ice grains. The major part of the event, however, would be propulsed by the gas phase of the volatiles, but potential minor liquids would boil off as well (and partially freeze, and subsequently sublimate) after exposure to the vacuum.

          • THOMAS says:

            Gerald, I thought that in "standard physics", all the ice was supposed to be sublimating furiously subsurface so as to be able to build up the required pressure to put on the amazing fireworks display we are seeing. How can there be any "ice particles" left in that blinding white mass of material above the huge white patch on the surface? 67P can't eat its cake and have it! There can surely only be dust particles there, and if the flash is indeed due solely to their reflective properties in sunlight as the standard model apparently requires, their albedo must be extraordinarily high. This places yet another severe constraint on the standard theory.

          • THOMAS says:

            @Gerald

            "Ice or just dust particles scattering the sunlight can easily look much brighter.”

            Sure, but the blog-post article doesn't speak at all of dust particles being "much brighter" in contrast with the low-albedo surface: it specifically makes a point of saying that "the activity is EXTRAORDINARILY bright", a very striking use of apparent hyperbole in a scientific article. In fact, the use of "extraordinarily" here should be understood in its original, literal, non-hyperbolic sense of "extra ordinary", i.e. "that which is not in the normal order of things".

            Your conclusion ("Nothing fundamentally mysterious. At least not for "standard" physics.") could hence not be further from the truth, judged objectively by the very terms of the article itself (and not just by me...). We are in presence here of what will shortly be seen as a truly historic image, showing a phenomenon which is way outside anything that the tools inside the tidy toolbox of "standard physics" are designed to cope with or account for.

          • Gerald says:

            THOMAS, besides silicates and organics the comet is composed of several types of ices (and possibly clathrates). Sublimating ices of supervolatiles can eject water ice besides dust.
            Even sublimating water ice could eject other water ice particles.

        • Harvey says:

          1). If the light is from scattered sunlight, it will have the sun's spectrum, slightly modified by variations of dust scatter with wavelength, scatter angle etc. A6000K ish black body plus some details.

          2.) If it is a discharge, the spectrum will be stuffed full of molecular bands and atomic lines and bear no resemblance to that.

          3). If it is 'hot reaction products', it would show a broadly black body spectrum (modified by variations of emissivity with wavelength etc) spectrum at a far lower temperature, 1200K sort of region maybe.

          Two instruments will already have yielded reams of data capable of differentiating those very, very different spectra. ALICE, the imaging UV spectrometer, and OSIRIS, which has a wide range of filters from near UV to near IR.

          So, if it is indeed 2 or 3 I am being asked to believe the teams have colluded to suppress the most dramatic scientific result of their careers. I don't believe that.

          If it is 1) why would they bother to say so? Since 2 and 3 have absolutely no scientific credibility, no one is going to bother to say explicitly 'the data is consistent with scattered sunlight'.
          But if it was 2 or 3 they would be booking their tickets to Stockholm with a publication.

          • Sovereign Slave says:

            Yes, the article has enough information to raise questions, but nothing specific or thorough enough to answer them. So we chase the tail of speculation while awaiting the pier reviewed paper. It would be nice to know what exactly the scientic team is seeking to understand about the event that they do not presently understand since they made a point of saying this, and how extraordinary the brightness of the light is. But if they found irrefrutable evidence of your 2&3 though, that would be such a cosmic game changer as to perhaps warrant a more measured response than simply booking a flight to Stockholm with publication in hand. For me, I could live with any of the options, though none are proven and seem very problematic in the details. Also, history is full of countless examples of things that were determined to have no scientific validity whatsoever, only to be proven quite scientifically valid in later times, so perhaps best not to fully rule anything out completely at this stage.

          • THOMAS says:

            @Harvey

            "So, if it is indeed 2 or 3 I am being asked to believe the teams have colluded to suppress the most dramatic scientific result of their careers. I don't believe that."

            Nobody is talking about any sort of collusion to suppress anything, Harvey.

            It's simply that the relevant ALICE and OSIRIS data has not yet been published (as is also the case with the crucial VIRTIS temperature data). As the article explicitly states, “the teams are busy analysing the data to understand the nature of these events.” Which strongly suggests that the acquired data is discordant with what was expected, otherwise they would have no problem understanding it. It’s simply going to take them time to publish it, as has been the case with most of the data from the beginning.

          • Jacob nielsen says:

            @slave
            Pier review?

          • Sovereign Slave says:

            @Jacob nielsen
            Well, that's where I usually review them, perhaps not too common with the non-fishing crowd though.

        • Harvey says:

          Capta problem, retry.

          As an amateur pilot, I've experienced a visual effect which I suspect is closely similar to this several times in early morning landings.

          The airfield reports calm conditions, with a thin mist layer but reasonable runway visual range reported by the airfield. (~ visibility on the ground.) The mist layer is often only ten or twenty metres thick, even less. Overhead the field, looking down, from say 2000 feet, the runway is clearly visible. But on approach, roughly into sun, all you see is a bright white surface - and no runway at all! Twice I've had to abort landings and circle till the mist cleared.

          Remember this is a snap shot. At the moment of the picture, there was simply a dense cloud of scattering dust close to the surface, giving a similar effect. You can deduce essentially nothing from its apparent brightness just looking at this, it depends on camera settings, dust particle size distribution, sun angle, etc etc. Or indeed it could be emission. There is no basis from its brightness alone to assert what it is. The spectrum however is diagnostic.

          It would be very helpful to know the sun position relative to Rosetta and 67P when looking at these. Generally one can figure it out. To date, except in perhaps a couple, the intensity has appeared consistent with scattered sunlight, and sharp-edged shadows are often evident. There have been maybe two of the many pictures which seemed inconsistent with that, and *might* have indicated intrinsic emission. They should be looked at carefully, but I'd probably just miss estimated the geometry.

          • logan says:

            Hi Harvey. Phenomena not being extraordinarily luminous, but reflective particulate being very close to NAVCAM? No doubt the scenario is highly complex 'ambiance' luminosity physics.

            On the other side the H. NAVCAM Team have the albedo, aperture and speed. Also the before and after shots. They know what we are guessing 🙂

          • logan says:

            Flying over the 'jet crown', NAVCAM and OSIRIS are going to be 'flared', no doubt. As positioning oneself at a 'glare angle' of a LED.

            But Outburst is at 2, not 6 o'clock. Neither believing that much on Near glitter, its 336 Km far, and inverse cube apply.

  • George Nixon says:

    It would appear from the violence of the explosive nature of the outburst, that the sublimating frozen substance or substances (not water ice) has been forcibly contained sufficiently long to enable the formation of plasma due to the combining of atoms, and or a combining of atoms and molecules. The confining over burden being weakened by heat and pressure, or suddenly weakened by thermal formation of fracture.
    If that area has been mapped, Rosetta may find a newly formed crack or sinkhole.

    • Harvey says:

      George: simply confining something under pressure does not form a plasma. The pressures concerned here are very low; even at enormously higher pressures, eg in a gas cylinder, no plasma exists.
      To form a plasma you have to expose the gas to the passage of a current, or ionise it in other ways such as by particle beam or UV illumination. You have to supply energy.
      Plasmas are formed if some source of energy raises the gas to very high temperature (eg the release of chemical energy in an explosion, nuclear energy in a bomb. ) but simply pressurising a cavity by sublimation won't do so.

  • Bob says:

    Wow reminds me of the white spots on Ceres

  • THOMAS says:

    What a brilliant picture (in both senses of the term)!

    Roughly 1km² (judging by the 1.5 km diameter of the circular white “patch”) of totally saturated pixels (saturated even in the original unprocessed image). The intrinsic brightness of the base of this particular outburst can hardly be denied, even by the most orthodox mainstream diehards. The non-sublimating-ice nature of this extraordinary flash is thus glaringly obvious (in both senses of the term)… Even ‘explosively’ sublimating ice, (whatever that might be…), presumably doesn’t release enough energy to produce this sort of white-out, imaged as it is from a distance of 336 km.

    This picture alone is thus sufficient to kill the ‘dirty snowball’ model stone dead once and for all. We eagerly await the corroborating evidence of high temperatures accompanying the discharge to unambiguously confirm the electric nature of the phenomenon.

    It would also be nice to have some information about how long this event lasted, for example by providing ‘before and after’ images, as was the case with the http://blogs.esa.int/rosetta/2015/08/11/comets-firework-display-ahead-of-perihelion/ post about the July 29 event. Such information is strangely absent from this new post.

  • John says:

    Was there any change in rotational speed detected that can be attributed to the outburst?

  • Marco says:

    This image is very reminiscent of deep impact's collision with Comet Temple. The jets are more omnidirectional rather than perpendicular to the surface at that point. The source point is extremely bright indicating a sudden high density of reflective particles. I would suggest that in a few short minutes, an amount of dust and gas has been released equivalent to several days worth of the ordinary jets at that point in the comet.

    It appears omnidirectional outbursts are happening mainly on the large lobe, while directed jets outbursts are happening mainly on the neck.

    I would suggest that omnidirectional jets are volatiles explosively evaporating near the surface, while directed jets are explosively evaporating tens of metres below the surface and being directed through cracks or tunnels that give them direction.

    • Kamal says:

      Marco: If I am right in believing that this flash and the previous one happened in the Anhur region, an interesting aspect is seen on the southern hemisphere map, that Anubis/Atum and Aker/Khepry form two sharp cliff-like boundaries inside which Anhur/Imhotep lies. So one could think of this also as a broad neck. The earlier jet captured on 29th July was also on the Anuket neck. The "omnidirectionality" might be simply because a large amount of dusty material is released, and this can happen if something falls down from the neck.

    • Marco says:

      This flash is from the border region between Imhotep and Kephry. It is a boundary with cliffs reminiscent of a fracture plain, but no, it is nothing like the neck and in no way similar in morphology to the neck regions.

      Kamal, I really don't know what you mean by something "falling from the neck". The only way to get a big sudden flash is a sudden release of stored pressure, which exposes a lot of reflective dust all at once, making the area very bright from reflected and refracted sunlight.

      This flash "fans out" so still straight lines indicating relatively fast escape speeds originating from the point where the breach occurred.

      This contrasts markedly from the Anuket outburst. The Anuket outburst was both directed and explosive, like a cannon rather than a sawn off shotgun, so I surmise some sort of vertical crack or tunnel to direct the outburst there.

      • originalJohn says:

        A return to a very bight "jet", needing no enhancement, 6 days after a barely visible jet. And hysteresis is no explanation. The radiation from the Sun is more or less steady, so the heat absorbed from six days ago is the same as the heat absorbed today. No pulses of heat to be delayed by hysteresis.

        Interestingly today's jet is more a fan. A fan with a very bright base (reaction zone) and a more diffuse uniform progression. Very much like a flame in appearance. In fact rather than brightening the image to see the comet nucleus better it would have been far more informative to reduce the brightness to see if any detail could be resolved in the heavily overexposed bright base zone of the fan.

        The favoured hypothesis has all the light of the jet (fan) as reflected sunlight, from dust particles. So the dust particles remain in a clump at the base, reflecting a lot of light, then, with an abrupt demarcation, spread out into a diffuse uniform sheet, reflecting a lot less light. All done by gas pressure from within the nucleus.

        Much more likely that the light emitted is intrinsic, intense at the reaction zone at the nucleus surface and diffuse in the discharged plasma beyond the reaction zone demarcation.

        We can speculate on all this from the appearance of the image but we are very fortunate to have the Rosetta craft right there and to have the assurance that the science teams are " busy analysing the data to understand the nature of these events". So we can safely assume that they will be measuring, indeed mapping, the temperature of the jets/fans, particularly any intense bright zones. And also analysing the ion content of the jets and the ions to neutrals ratio.
        Hopefully they will also find it worthwhile to measure the proton current density close to the reaction zone.

        Whereas for a hydrocarbon combustion reaction at the nucleus surface a temperature of 800-1000 deg Celsius would be
        reasonable, these bright outbursts are likely to be plasma discharges in arc mode in which the temperature expectation would be several thousand deg Celsius.
        Sublimed ice as gas would on the other hand be expected to exhibit a temperature of say -70 to -150 deg Celsius.
        Not much chance of confusion there then. We await the results with interest.

        • Gerald says:

          The temperature of the ices depends on their composition, but you are right, water ice would sublimate rapidly above -70°C, although larger fragments of water ice could survive for some time above this temperature, but in a rather active state.
          Dark fluffy dust can heat up in the Sun to above 100°C, but certainly not to 800°C in the observed settings.
          Infrared spectra will (have) return(ed) a clear temperature profile.
          My "prediction" is, that we will see no (black-body) temperature above 200°C in the dust jets.
          The only possibly misleading exception may be some excited atoms by uv or rare solar wind collisions, leading to emission lines corresponding to higher energies than the thermal emissions. But the infrared continuum spectra will talk a clear language, easily distinguished from emission lines caused by ionizing radiation.

          Originaljohn, you don't like the delayed heat-up of subsurface supervolatiles (hysteresis), because it easily explaines the outburst.

        • Harvey says:

          BTW for anyone having Capta problems - it doesn't know the difference between a peanut and a cashew nut!!

    • Kamal says:

      Marco: Sorry to have been unnecessarily cryptic.

      I was trying to point out the fact that there are cliffs nearby, and that there may be other causes for omnidirectionality, such as boulders falling off a cliff onto a plain and raising a lot of dust. If one exaggerates to some extent, this is what may have happened in the Deep Impact case where you had an artificial "boulder" falling from far above.

      You are right that the morphology here looks different from the neck between the two lobes, and a different mechanism may apply for the Anuket jet.

      Kamal

    • Sovereign Slave says:

      I do have a related question. Has there been any scientific data or instrument measurements to date that have clearly measured how deep (and to what temperatures) the sun's warmth is penetrating the surface of P67, or is it just pure assumption (presumption) that it does so at all?

      • Sovereign Slave says:

        To clarify my above question, it was in response to your comment above Marco that "I would suggest that omnidirectional jets are volatiles explosively evaporating near the surface, while directed jets are explosively evaporating tens of metres below the surface and being directed through cracks or tunnels that give them direction."

        The whole sublimation theory is based on heat from the sun significantly penetrating the surface of the comet. Is there any scientific data that measures temperature per depth on P67 at varying distances to the sun - surface temperature at this distance is blank, at 1cm blank, 2 cm blank, 1 meter, etc? Or, is sublimation based on a huge assumption that just takes for granted that heat is capable of penetrating to all the necessary depths without any scientific hard facts backing it up?

        • Marco says:

          Sovereign Slave,
          To clarify, the outbursts are best explained by stored pressure being released by a surface breach. I explain that by explosively boiling liquids (hydrocarbons etc.) while sublimation theory explains it by supervolatiles which generate high pressure even at much lower temperatures well below the surface.
          In sublimation theory the temperatures are inferred to be colder the further down you go.
          Stretch theory requires a more complex thermal transport meaning that the interior can be warm and pressurised to a varying extent all the way to the core of the comet. The sun is still the source of the thermal energy, and all established thermal equations still apply, and no electricity is required, nor combustion.

      • Gerald says:

        It's mostly inferred by the composition of the released volatiles, and by physical models.
        Philae tried a direct measurements. But he failed to penetrate the surface. Although he measured at least the surface temperature.

      • Gerald says:

        Sorry, forgot to mention the obvious: Thermal conduction has been investigated since centuries in very detail:
        https://en.wikipedia.org/wiki/Heat_equation
        The Wikipedia article is of course just a glimpse to the research on that topic.
        67P is composed of ordinary matter. So it behaves like ordinary matter, and it's qualitatively known, how it behaves. But quantitative values can just be narrowed down by observation and modelling.
        Would be easier with an operational Philae.

      • Harvey says:

        MIRO can give data on that but only to pretty shallow depths. I've not seen any data from it of late. VIRTIS surface temperature measurements of course will also help.

        The sun's heat will inevitably penetrate; the question is how far, how fast. Basically, why would it not? - there are no perfect thermal insulators - not even vacuum, you get radiative transport.

        That's a classical problem of thermal diffusion, and depends on the thermal conductivity and specific heat of the material. Given the low density, both parameters are certainly low, which means the thermal response is 'slow'.
        Generally in thermal diffusion the penetration depth only increases as the square root of time; twice the time only increases the penetration depth by 41%. So given that we have passed perihelion, heat will not penetrate *hugely* further into the comet that it has already during the rest of Rosetta's likely observation time - though it will somewhat.

        I imagine we will eventually see a lot of analysis of this.

  • logan says:

    Hi Marcin. Philae is somewhere around the back of the head of Ducky. This outburst, -the more gigantic light show until now- is at the south side of Ducky's base.

    ......

    Explosive, hardly collimated.

    Seems navigation is deriving a little over terminator line, toward the action. This gallery shot missed if not.

    'Shining' follows the surface of Imhotep. Fresh material flowing? Or just the reflection of the plume?

    Congratulations to all Teams. Specially H. NAVCAM!

  • Gerrit says:

    Are we going to see a new sinkhole in this region?

    http://blogs.esa.int/rosetta/2015/07/01/comet-sinkholes-generate-jets/

  • Dave says:

    Was the comet singing during this explosion of dust and if so was there an electric current generated perpendicular to both solar and magnetic field?
    Has the field changed must now that the activity is higher than the 3000 occurrences measured prior to Nov 2014

  • Dave says:

    Sorry must should read much

    Fat fingers small phone

  • Dave says:

    Kamal,
    Re deep impact, I am not sure you can use the deep impact as a model, as you state its artificial.
    More important a boulder falling off a cliff would probably bring other debris down with it, and if it's loosely packed and porous as alleged then not only would grownd dust be disturbed the debris falling down could also break up and scatter causing more dust.
    The deep impact probe would probably falling faster, although low G here and it's a completely different material and completely different shape.
    Unfortunately although sublimation is taking place the details of how it manufactures deep pits and parallel jets plus this fan of jets is still very difficult to imagine. I am not sure deep impact helps at all.
    Regards

    • THOMAS says:

      @Dave

      "Kamal,
      Re deep impact, I am not sure you can use the deep impact as a model, as you state its artificial."

      It’s “artificial” in the sense that the huge explosion and accompanying flash were man-made, by Deep Impact’s 370 kg copper impactor being deliberately slammed into comet Tempel 1. But what is truly interesting here is precisely that the main Deep Impact flash (http://www.nasa.gov/mission_pages/deepimpact/multimedia/pia02137.html#.VedygX3IiSp) bears such an extraordinary resemblance to the August 22 event on 67P, whereas the latter is hypothesized to be due to sublimating ices. I’m not sure which of the two events can be a “model” for the other… It would seem more logical to assume a common cause for these two strikingly similar flashes/explosions. I develop this line of enquiry in my post http://blogs.esa.int/rosetta/2015/08/28/cometwatch-22-august-2/#comment-524097 of four days ago which is still “awaiting moderation”, but hopefully not for long now.

      • THOMAS says:

        Sorry, the above comment (http://blogs.esa.int/rosetta/2015/08/28/cometwatch-22-august-2/#comment-524097) actually failed moderation, I don't know why. In it, I pointed out that the MAIN Deep Impact flash captured in the image was preceded a couple of seconds earlier by a much smaller, distinct initial flash which took the Deep Impact science teams completely by surprise but which had been explicitly predicted by the leading EU theorist Wal Thornhill in a set of predictions posted 24 hours *before* impact…

        Given the striking similarity between the Deep Impact flash and the 67P August 22 flash, it would seem logical to conclude that the two flashes were produced by the same energetic cause, i.e. a huge electric discharge.

        • Gerald says:

          An electrical discharge would have left an electromagnetic signature across the spectrum, easily detected and identified by Rosetta's instruments.

          Scattered sunlight is the straightforward and consistent explanation.

  • Jean-Pierre Pericaud says:

    That''s just stunning !
    Better than Armstrong on the moon !
    But french medias have others problems at this time, and nobody speaks of the fantastic shots from Rosetta.

  • danny says:

    I have a question for COSIMA invetigators. Is there an increase in sodium and magnesium after the out-bursts?

  • Claudia says:

    Just a friendly reminder to all commenters to please keep comments relevant to the topic of the original post and, most importantly, to use respectful language when responding to other comments.
    Any further comments submitted on an unrelated topic and/or deemed aggressive or unnecessarily rude will not be published. Please have a look at the blog house rules here: http://blogs.esa.int/rosetta/2015/01/06/happy-new-year/

    Thanks for your co-operation!

  • Claudia says:

    And to answer to the various questions that were posed in this thread, the science teams are of course analysing in detail the data and images they collected during this and other similar events, and we look forward to seeing the results of their analyses in future papers.

    Best wishes

Comments are closed.