Last stop before close flyby – CometWatch 9 February

Today’s CometWatch entry is a single frame NAVCAM image taken on 9 February from a distance of 105 km from the comet centre. The image resolution is 8.9 m/pixel; the processed image below has been slightly cropped to eliminate vignetting in the upper corners, and measures 8.5 x 8.5 km (the original, provided at the end of the post, measures 9.1 x 9.1 km).

NAVCAM image taken on 9 February from a distance of 105 km from the comet centre. The exposure time is 6 seconds. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

NAVCAM image taken on 9 February from a distance of 105 km from the comet centre. The exposure time is 6 seconds. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

In this orientation, the comet’s small lobe is the foreground and the large lobe is in the background. Particularly stunning is the delicate, ethereal glow of activity that contrasts against the shadowed region between the two lobes. From this viewing position the outflowing material seems to take the shape of a broader fan, rather than the more collimated jet-like features seen at other angles.

As seen in previous images, the sharp vertical shadows seem to be a result of the large lobe casting shadows down across the neck of the comet and towards the head. There is very little back-scatter illumination around the neck itself, but a diffuse ‘glow’ can be seen against these dark shadows where a broader ‘atmosphere’ is visible above the surface of the small lobe.

Rosetta's closest approach during 14 February flyby. Credits: ESA

Rosetta's closest approach during 14 February flyby. Credits: ESA

Rosetta is now less than 24 hours from its close 6 km flyby of the comet – closest approach tomorrow occurs at 12:41 GMT (13:41 CET) above the Imhotep region. The NAVCAM is scheduled to take images 1-2 hours before and after closest approach, when the spacecraft will be between about 8.5 and 11 km above the comet surface. These NAVCAM images will be downlinked to Earth Sunday/Monday and – depending on availability – we hope to be able to share one of these images with you as Monday’s CometWatch entry.

Meanwhile the OSIRIS team expects to get their images back some 5-12 days after the flyby, and therefore anticipate releasing an image within about two weeks of the event. The delay is due to data buildup in the spacecraft’s mass memory (which NAVCAM does not suffer from) and, furthermore, the bit rate is particularly low at the moment because of the relative position of Rosetta to the Earth – essentially on the opposite side of the Sun (you can check the situation with our Where is Rosetta? tool for today's date, for example).

Rosetta has ten other scientific experiments that will also collect data during the flyby. The spacecraft will also pass through a point where the Sun is directly behind the spacecraft, allowing the instruments to make unique observations of the comet surface and compare it with measurements made over a large range of illumination conditions. This will offer further insight into the physical properties and composition of the surface material, which in turn will help unravel the mechanisms that trigger cometary activity.

Indeed, the spacecraft will make valuable in-situ measurements of the inner coma, to sample the region where the comet’s coma is born. This will help scientists gain a better understanding of the exchange of momentum between the dust grains and gas molecules, testing mechanisms that have previously only been modelled theoretically.

Following the close flyby, Rosetta will move as far as 250 km from the nucleus. The trajectory also increases in inclination, to allow the instruments to take measurements over a large latitude range.

For more information about the close flyby, read our preview story: Rosetta swoops in for a close encounter

The original 1024 x 1024 frame for today’s CometWatch entry is provided below:

ESA_Rosetta_NAVCAM_20150209

Comments

49 Comments

  • dave says:

    Fierce Jets, thanks ESA, fabulous picture.

    I cant quite make out if the origin of the jet is from an area beside the dustiest part of the neck.

    Great picture all the same, first time we have been so looking down the barrel, but the source is obscured by the dust. Some views in different wave lengths to go with it would be nice or some detail from this spot from the plasma guys.

  • Ross says:

    Seems like a lot of activity is occurring in the shadowed neck regions. This should be the last place to produce heavy activity in the sublimation model.

    • Graham Hall says:

      As you say the neck is shadowed more than the top of the lobes. However, the neck area seems to be composed of different materials than the top of the lobes.

      So the lobe material is perhaps denuded of volatiles, or they are deeply buried under some form of crust, whereas the neck area is more exposed, particularly where a crack exists in the observed surface. This crack also has a number of pits associated with it. The neck area in fact seems to get hotter than the top of the lobes, perhaps because the material there absorbs radiation better than the lobe surfaces. Clearly there's at lot to learn still and the paper papers released in Science recently were submitted in October 2014, to give time for peer review prior to publication., so we're looking at evidence not covered in the papers.

      But at least these papers support the sublimation model and have been peer reviewed and published. If you have any links to different views with equivalent credentials we'd all like to hear of them.

  • Bill Harris says:

    Whoa. Duelling Mods!

    You and Claudia (as well as the Navcam Team) keep outdoing each other this week. The views keep getting nicer.

    Next week is going to be spectacular!

    --Bill

  • Daniel says:

    Well wow, that's an impressive image. I admit to being disappointed that Rosetta is generally further away from the comet now, but it sure can deliver spectacular views of 67p anyway. Okay so the unmodified image isn't perhaps that special, but the tweaked one is. Thanks emily!
    It's not the inactive comet we saw back in August, that's for sure. It once again makes you curious as to just how the interplay between sublimation and the structure of the comet works to result in these emissions.

  • Judy Hawkins says:

    That is so beautiful: the shadows on the jets, and the layers of shadows showing the multiplicity of the jets: stunning photography,.

    Kudos to the folks pointing the cameras!

    Judy

  • Gordon Jenkins says:

    Lobe Separation.
    We know comet separations happen because of what happened to Comet Shoemaker–Levy 9.
    Have the flight dynamics and operations teams taken into consideration the possibility or eventual probability that the two lobes will eventually separate? What effect would that have on the gravitational pull? Which lobe is preferred for tracking and science purposes if it comes down to either/or scenarios? In event of lobe separation would that increase the chances of re-establishing contact with the Philae Lander.

    • Gordon Jenkins says:

      The pieces coming off this comet right now, the major crack in the neck portion between the lobes, vapor outgassing at the neck region all seem to point to a major separation event is either occurring or is imminent, even if it just means a reshuffling of lobe positions around a gravitational barycenter.

    • Gordon Jenkins says:

      Is the outgassing from the crack at the neck region due to compression from gravitational forces trying to pull the two lobes closer together? Or is it a crack due to tension from unbalanced centripetal and reactive centrifugal forces in the spinning comet trying to tear the comet apart?

      • Ross says:

        What makes you think the 'outgassing' is from the crack? What makes you think that the gas comes from beneath the surface at all? Because the scientists said so? Have you observed any image of any vent forcing the gas into these collimated structures?

        I understand these astrophysicists are mich smarter than I and we should trust their opinion, but as a scientist I will also acknowledge the possibility that they're wrong. Sublimation is NOT the only possible mechanism which can produce the phenomena we're observing.

    • Mike says:

      When this comet separates. the smaller lobe will orbit the larger one. Rosetta will still be able to maintain an orbit . Philae on the other hand may be launched from the surface by volatile emissions. If that has not already taken place. It should also orbit the comet until gravity eventually brings it back down to the surface. Perhaps ESA will get lucky and the Lander will be awakened from its sleep. It has gathered important data in the 57 hours it was operational. However, I would like to see it complete the mission for which it was designed.

    • Mike says:

      Comet 67P and Shoemaker-Levy 9 are both comets. That is about as far as he comparison goes. Shoemaker -Levy 9 was on a collision course with a Giant body whose huge gravitational pull brokeit into several fragments before colliding with the planet. Comet 67P is traveling in an elliptical orbit around the Sun. It has not passed close to the large Gas Bags in the Outer Solar System. The forces acting on it at the moment comes from the Sun and internal volatiles turning to gas. I will be surprised if ti breaks up on this pass.

  • John Blacow Australia says:

    I hope Philae can come back with data. Waiting to receive Rosetta's data. This is a fantastic opportunity to learn so much, thank you ESA. Where will they go when they leave us? What fantastic time capsules they make and I wonder who will find them?

  • Dave says:

    The more I look at the main jet, it looks like at the base there is a bright circle that's at least twice the diameter of the dust jet.
    This bright circle on the ground looks odd if it was from sublimation from a hole.
    It looks more like there is a hot circle on the surface below the jet.
    There can be a couple of explanations for a local large hot spot on the ground, however is you rule out some sort of magma chamber underneath the surface then it looks more like an electrical effect.
    The article that's been posted for sublimation from below ground needs a small hole and the same article rules out porous surface with gas exiting under dust.
    It's still difficult to understand the mechanism, anyone else got some alternatives?
    Great great picture though, my favourite by far, can't wait for this weekends close up pictures and some other data to allow us make better guesses

    • originalJohn says:

      You are right Dave. It looks like a hotspot. THOMAS has observed many times that the infrared temperature map published a while ago by ESA showed a hot strip in the valley where the jet activity was, despite it being a shaded region. No comment or acknowledgement of this by ESA. And Sovereign Slave has pointed out that the jets are too consistent and regular for sublimated gas at random holes and cracks. Again no comment from ESA. And I have proposed that a combustion reaction could be taking place combined with plasma discharge jets, a reaction between hydrocarbons on the nucleus surface and oxygen from the rock, activated by proton energy then strongly exothermic and self sustaining. Consistent also with the principal constituents of the coma, H2O, CO2 and CO which are hydrocarbon combustion products ( more detail on this on January 21 post). And consistent with the apparent hotspots. No comment again from ESA. Specific temperature measurement of the surface from where the jets emanate and of the jets themselves would resolve this beyond dispute. Pressurised jets of gas would be cold at the surface and colder further from the surface. It will reach a point soon where it will be untenable to continue talking about gas sublimation when all opportunities to confirm or refute it have been ignored.

      • THOMAS says:

        Originaljohn,

        For easier reference and discussion, I've screen-captured the two most intriguingly anomalous temperature stills and published them on Flickr:

        https://www.flickr.com/photos/130179313@N03/16524318826/

        https://www.flickr.com/photos/130179313@N03/15927644524/

        (Credits: AGU/ROSETTA /VIRTIS/Fabrizio Cappacioni)

        • originalJohn says:

          Good work THOMAS and thanks for that. Both images are easier to relate to than the global projections they have also published. It is amazing that they do the map presumably because temperature distribution is considered significant and they comment on morphology causing temperature gradients and shading in the neck area then fail to observe the literally glaring anomaly of the hot line along the valley floor and the large hot patch at one end of it. The white of these regions is indicated on the scale as 220 deg K but being white it is saturated and should be indicated as .> 220 K, and who knows by how much. This is another reason why the white areas demand further investigation. One of the most significant features of the results so far, and it and its correlation with the jet emission only commented on by you. Hopefully there is a whole stack of follow up data yet to be published.

          • THOMAS says:

            @ Originaljohn

            I honestly do not believe that such a clearly significant finding can be ignored and/or remain unexplained indefinitely. And mission scientists must indeed have collected heaps of data on the correlation between jet sources and surface temperatures: this must always have been one of the most obvious and urgent mission objectives…

        • Jacob Nielsen says:

          @THOMAS, agree with you: hot areas coinciding (?) with sublimation is NOT what would be expected. Some exciting discoveries ahead?

      • Harvey says:

        Do, please, provide more detail of this strongly exothermic reaction between rocks and hydrocarbons.
        Since it apparently readily occurs at low temperatures and pressures, it should be dead easy to initiate on earth. Bit surprising oil reservoirs don't go up in underground Flames really isn't it, lots of rock and hydrocarbons in close proximity. Ceramics seem remarkably stable in the presence of hydrocarbons, even at high temperatures.

        So what *exactly* are these self sustaining, exoteric rock/hydrocarbon reactions, where have they been observed?

        • originalJohn says:

          Not surprising at all Harvey, for the same reason that lumps of coal do not spontaneously ignite surrounded by oxygen in air. Do you think just fuel and oxygen are required. Wrong then. That would be the special case of hypergolic
          combustion. Otherwise an energy input is necessary to activate the reaction. Do you know how to light a fire? Thereafter the exothermic nature of the reaction sustains it without further energy input.
          The rock of the comet nucleus covered in a layer of hydrocarbons would not be expected to react either. But it is another sort of special case, perhaps a unique one. It is sitting in a flux of high energy protons. It seems that they provide the activation energy to dissociate the oxygen and initiate the reaction. The reaction may or may not be fully self sustaining depending on the energy balance. It would fit observation better if it still required a small continuous energy input from the protons to provide sustained activation. The relationship of comet activity to the Sun would then be upheld.
          The quantities of hydrocarbon and rock available mean that prodigious quantities of water would be produced. Not a process that would occur naturally on Earth though as we are largely shielded from the proton flux. A special case and one that I have called energetic proton combustion. Ab initio Harvey, ab initio.

          • Harvey says:

            What is the exothermic self sustaining reaction you claim exists?

            A few facts.

            The most resistant chemical ware is fused silica; about the only thing that attacks it is hot aqueous NaOH and aqueous HF. We use silica furnace tubes in contact with hydrogen at over 1000C for years, alumina tubes with a silicate binding phase at over 1500C
            Carbon 'paddles' are used in contact with silica at above its softening point by Glassblowers with no reaction.
            Tons of silicate zeolites are used in contact with high pressure hydrocarbons at temperature up to c650C all day every day in oil refineries.
            Oil reservoirs intimately mix silica/silicate and hydrocarbon, and contain lots of helium in some cases - the result of alpha decay of radioactive elements in the rock; MeV particles to initiate it.
            Ceramics, most silicate containing, are routinely used in innumerable applications at high temperatures in contact with hydrocarbons.
            Reducing silica/silicates is notoriously hard; the standard Ellingham diagram shows C reduces it *above1620C*.

            So *WHAT IS* the self sustaining reaction, what is the exotherm, where can I see it happening?

            It's even hypergolic? What do I mix silicate with to see it burst into flame? (The answer is actually ClF7, ClF5 and F2, probably in short supply on 67P.)

            Just a nice simple chemical formula, with x kcal/mol exotherm. This is a GCSE level question.

        • Marco says:

          Hi Harvey, I don't really understand what you are saying here. Are you denying that there are hot spots that cannot be explained by there being more sun there, because there is less sun there. You are challenging people to think of other reasons why it would be hot there so you can make a straw man out of it so you can ridicule any new ideas that may come of it. I don't care for "exothermic reactions", much less electrical universe dogma. If there are some good new ideas out there, you are unlikely to give them a fair hearing at all, though. Or perhaps you will just ignore them, I don't know.

          • Harvey says:

            A specific claim was made that the water etc result from an exothermic self sustaining reaction of the silicates with hydrocarbons.

            The evidence I see suggests that no such reaction exists, and that to drive such reactions thermally requires temperatures typically in excess of 1500c, just a *little* hotter than 67P, and requiring massive power input.

            If such suggestions are made they need evidence.
            I don't think it exists.

          • Harvey says:

            'Fair hearing' does not equate to 'uncritical acceptance of unsubstantiated wild speculation'. The difficulty I have with ignoring such stuff is that it may mislead those who are genuinely interested but lack background knowledge.

          • Marco says:

            I understood it to be a not specifically silicate at all. Ie. An exothermic reaction of hydrocarbons(etc.) with Oxygen. Of course, oxygen isn't necessarily available, certainly not as Native O2, so a disassociation reaction was suggested. I can imagine the possibility of an exothermic reaction that doesn't involve silicates, but not knowing what compounds are in there combustion is idle speculation anyway.
            However, the Hapi valley temperature anomaly may need to be explained by an internal source of thermal energy. If it is both warmer and sublimating more there (sublimation would reduce the temperature) it can't be explained by just the sun and thermal inertia.

          • Harvey says:

            So now we have some totally mysterious, unknown, source of oxygen. This is fantasy land. Free oxygen happens to be a gas. The vast majority of the oxygen is bound up in silicates of various complex type, and also in Al/O containing compounds, which are even harder to reduce!

            I had to get a chemist friend to check, because I wasn't quite sure how to do the sum, as the Si=O double bond doesn't exist unlike C=O. He calculates he prototype silicate/hydrocarbon reaction 2SiO2+CH4->2Si+CO2+2H2O to be 1062kJ/mol ENDOTHERMIC .

          • originalJohn says:

            Harvey you seem to miss the point. The self sustaining exothermic reactions I have referred to are those of the reaction of hydrocarbons with oxygen, all strongly exothermic. I have observed elsewhere that as the potential oxygen source is
            the silicate rock additional energy would be required to release the oxygen from the Si-O bond. The reaction would not therefore be sustained without that additional energy input. I have surmised that additional energy is supplied by the solar protons, to liberate oxygen and allow the exothermic combustion reactions to activate and proceed. These are two distinct processes. Proton induced release of oxygen and proton activated combustion of hydrocarbons in the presence of oxygen. As there is not a flux of protons in your lab with energies in the keV range what is happening or not to fused silica on your bench is of no consequence. If you are interested in possible alternative sources of comet water you are unlikely to find them there. It needs an extension of thinking and perception. If though you are simply in the business of propping up the ice model then you will invoke any irrelevance that suits you. Pity you can't invoke some ice.

            By the way, you choose also to understand that I suggested hypergolic combustion might be involved. Read again. I was observing that your sarcastic surprise that oil and rock did not spontaneously ignite on Earth was unfounded as they are not hypergolic.

      • dave says:

        Hi,
        originaljohn,
        I like your combustion idea, however its a very long time since I have needed to use chemistry. I have had similar thoughts myself, but my chemistry is now to incomplete for me to judge.
        If there is no significant ice detected, then it is surprising that relatively few people are trying to think outside the box to explore other avenues, it might just trigger something.
        After all its only a blog and we should be ok to think out loud now and again.

        • originalJohn says:

          You misunderstood again Harvey. No specific claim was made. A specific suggestion was made. I am in no position to claim anything and neither are you. And suggestions don't need evidence. They need viability. To separate the Si-O bond requires an energy of 4.68 eV. Perfectly viable at the energies ascribed to solar protons.
          You see yourself as a gatekeeper. In fact you are expressing an opinion. Nothing more.

        • originalJohn says:

          Your chemist friend is correct Harvey and Gerald has already drawn attention to the endothermic nature of that reaction and quantified it. It is however an overall reaction, a summary of numerous intermediate reactions that take place. It does not include the energy input from the proton flux and this is a required first stage to liberate oxygen. As I have observed before the Si-O bond energy is 4.68 eV and silicates are all single bonded. The arrangement is however tetrahedrally coordinated so the energy input for the full stoichiometric reaction must dissociate four single bonds. Oxygen is nevertheless released as soon as the first bond is separated. The reaction does not need to be complete to provide oxygen for the exothermic combustion reaction. The combustion reaction may not be complete either and incomplete combustion products such as CO, atomic H and HCHO have already been identified in the coma of this comet.

    • logan says:

      Shock wave of the main jet? 😉

  • Cometstalker says:

    And you still have no clue what causes the outbursts?

  • Cordell says:

    We can clearly see where all the current activity if focused. Does this mean the comet will split in two eventually....and to what extent will the segments separate??

  • Bob says:

    It would be nice if on the near flyby on Valentines day as Rosetta 'kisses' the comet , if a photo of philae's new location were to emerge.

  • Rod says:

    Which image is most like what I would see from Rosettas' position?

  • Mike says:

    It is obvious to me in this image that the volatiles are concentrated in the neck. Which explains why this body is two lobed. Also the probability that it will eventually separate is increased proportionately. Probably not on this pass but certainly in future visits around the Sun.

  • logan says:

    Hi Robin. Time to bring back to foreground your cryovolcanic arguments 🙂

  • logan says:

    Hi Emily and H. NAVCAM Team. The eclipsing of 'Coraline' Particle-o-sphere is impressive!

  • logan says:

    Are we starting to see a 'true' atmosphere' around Ducky's head?

  • logan says:

    See how the delicate solar jetting of the head meet the powerful cryovolcanic eject of the body!

  • logan says:

    Main cryovolcanic eject is parabolic-ally deflected to the left by Ducky's head 'atmosphere'.

  • Dave says:

    Thomas & original john, thanks for the information on temperatures in the neck. I am surprised that such an anomaly was not mentioned in the presentation, even if only to discount the importance of it.
    You are right it does not make any sense if sublimation is supposed for the mechanism in the neck.
    The other feature of the jet photo is that it looks like the dust jet is centred on a large rock or other protrusion at the centre of the bright spot. This again rules out sublimation from under some sand & tends to support an electrical origin. I admit that it is difficult to be sure with the dust obscuring the source.
    With such a clear view down the jet to its source there must of been plenty of other instruments running, let's hope we see the results.

  • logan says:

    See how solar jetting is perpendicular to surface. Specifically that square facet left of Ducky's head.

  • JP says:

    Looking at the shape of the jets, I am wondering if the initial estimate of the nucleus through Hubble space images (the erroneous rugby ball shape) could have been caused by a strong dust emission around the neck.

    This is not really sexy science for Rosetta, but taking back old data sets obtaine don 67P (Hubble and VLT), and developing a model which fits these data to some more real shape would certainly help a lot small bodies shape estimation.

    • Harvey says:

      Depending on when they were taken, there may not have been any dust.
      The neck simply wasn't resolveable. There are well established methods to deconvolve an observed image using the PSF of the telescope, but you can only push things so far. It's notoriously easy to start 'seeing things that aren't actually there.' So the 'rugby ball' will almost certainly have been the 'best estimate' under the constraints of the data and a statistical 'best guess'.
      Such algorithms can be trained and tested on as many test data sets as the developer likes, so it's not really clear there are any specific lessons for the method here.

  • JP says:

    You are right, most probably, there was not dust around.
    VLT and NTT data were acquired much later, I went quickly through the paper.
    They used a rotation period of around 12 h (from Hubble paper?), and a convex shape model. With this starting point and boundaries, it is of course difficult to reach a sensible modeling of *this* comet 😉

    The residual modeled photometry error is quite large (if I understood well the VLT paper) for a complex model. Therefore I think there is probably quite some room for bringing in new (or old) methods, simple to start with, which would compete advantageously.
    But I suppose anyway an old post blog comment is not the best place to get the attention of planetary scientists...

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