CometWatch 22 March

This single frame Rosetta Navigation Camera image was taken on 22 March 2015 at a distance of 77.8 km from the centre of Comet 67P/C-G. The image scale is 6.6 m/pixel and the 1024 x 1024 pixel image measures 6.8 km across.

Cropped and processed single frame NAVCAM image of Comet 67P/C-G taken on 22 March 2015 from a distance of 77.8 km to the comet centre. The processed image is cropped and measures 6 x 6 km. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Cropped and processed single frame NAVCAM image of Comet 67P/C-G taken on 22 March 2015 from a distance of 77.8 km to the comet centre. The processed image is cropped and measures 6 x 6 km. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The image above has been processed to bring out the details of the comet’s activity, while also emphasising details on the nucleus.

The image presents another interesting view of regions previously cast in shadow, particularly on the small lobe around Hatmehit, and of the topography on the large lobe close to Aker and Khepry. (The 9 March image also offered a new view of these regions, from a slightly different angle).

At the bottom right, the large lobe is casting a shadow over the broader ‘atmosphere’ around the comet.

The original 1024 x 1024 image is provided below.




  • THOMAS says:

    I observe that as 67P gradually but steadily turns its "dark side" to the Sun, the newly-revealed regions which were previously in shadow are looking, if possible, even more uncompromisingly rocky and rugged than on the face we discovered 7 months ago.

    Seriously, can this simply be a random agglomeration of dust and ice with the density of a champagne cork?

    • ianw16 says:

      Hmm, there's a thought. I just cut through a piece of cork with a not particularly sharp knife. When I looked at it through a hand lens it bore striking similarities to the pics above. Given the density of the object, and the resemblance to cork, could it actually be cork?
      I'd say about the same chance of it being rock. So about a million to one!

      • dave says:

        If the comet was cork like, then maybe the bounce would not have been so high, maybe we would have already found Phillae

  • andrew says:

    i think it is a wonderful shot of the comet but will it break in half

  • manuel gomes says:

    Some call it the (ugly little) duck;
    some say it looks like a sphynx;
    this real smoking gun is now beyond Mars,
    half way from Earth to Jupiter, ready to ignite
    and freely to ask the questions we may answer,
    if we can

  • logan says:

    Didn't want to comment, but jetting in the neck's shadows seems aligned to dominant layering. [The omnipresent salvo: Could be perspective].

    • THOMAS says:

      I honestly think this a chance occurrence, Logan.

      Whether they are due to standard theory "outgassing" or, on the contrary, electric discharge, the jets are, at their point of origin, necessarily perpendicular to the surface plane concerned. (I suppose the proponents of each model can agree on that, at least, even if the attributed causes are diametrically opposed ...).

      As to the cause of the observed *bending* of certain jets, to different degrees, in precise places, the jury is still out. It is 67P itself which, over the coming weeks and months, will act as an arbiter between the two competing theories, thanks to the massive archives of acquired ROSETTA images and data which will eventually be made available for public scrutiny.

      • logan says:

        Well, THOMAS, think of another models. Think on new models 😉

        Glad to see you indefatigably fighting.

      • Ross says:

        Looks like the formation of 'crater chains' or 'sinuous rilles' so commonly observed on planetary bodies.

      • Marco says:

        Hi Thomas. I always laugh when you say "two competing theories". Yes. 67P will be the arbiter between a myriad of different expectations of possibilities - some of which have been naively pigeonholed into a (false) dichotomy. I guess I will keep on laughing when both sides of the dichotomy keep getting "surprised". Not much point going to a comet if everything is as predicted. Huh.

      • harvey says:

        Actually, neither theory constrains them to be perpendicular, except for EU with a conducting body.
        For EU with an insulating or high resistivity body (ice, rock...) the field can point any direction.
        And for say a subliming jet emerging from between the 'layers', it could emerge tangentially to the surface.
        So no, sorry, cant agree with that either 🙂

  • Jim Robertson says:

    With half the "neck" hidden in shadow, it looks fragile. I can easily imagine the neck area breaking, and the two mountains of icy dirt falling together, to meet at another place and form another neck. Rotation would speed up, and the axis would shift as to conserve angular momentum. Such an event would be accompanied by a large flare-up in the coma from ejected dust. That probably does not happen on every perihelion, however.

    Perhaps that is the origin of those flat facets we see on the lobes? They are places where the lobes were previously in contact?

    Over time, debris would accumulate around the new neck, but it would also be a site of slightly warmer weather as sunlight is captured by the "canyon".

    Clearly my earlier thought of the neck forming around the equator of rotation is unlikely, since such a rotational axis would be unstable.

    I'm only a casual armchair observer, of course, and not any kind of expert in the dynamics of this thing. But for what it's worth, I don't see any evidence of electricity in the "bent" jets. I see an uneven distribution of escaping gas, with more coming from the canyon around the neck region, and that outflow distorting the path of the dust jets as they leave the body in a path essentially normal to the local surface where they originate. Not that it isn't possible for this object to develp a static charge, of course..

    Thanks for the great pictures, Emily! Keep 'em coming!

    • Marco says:

      Hi Jim,
      By my rough calculations of angular momentum versus kinetic energy, a collapse of the neck and inwards movement of the head lobe would accelerate the rotation relative to the body lobe rotation first. The neck either side of any break would rotate well away from the mutual centre of gravity. Thus, each impact would significantly shear and shatter the other lobe destructively as the only way to conserve angular momentum when they re-collide... At least the way I understand the maths of it at this rotation rate.

      • Jim Robertson says:

        I wouldn't know how to begin those rough calculations.

        You have a body (or bodies) made of a substance which resembles freeze dried ice cream, or maybe just a little denser than an aerogel. It is cold enough that molecular nitrogen exists as a solid. How strong is this material? How brittle or resilient? The only information we have is that it appears solid. And it is extremely heterogeneous.

        In its current configuration, with its 12 hour rotation period, it must be pretty close to coming apart into two bodies in orbit around each other.

        But it is hard to guess what it must be like, temperature in the low tens of °K, pressure is a pretty-good vacuum (better than your average chem lab), and the object exerts a gravitational force four or five orders of magnitude weaker than our familiar 1G.

        So it's a fair question: if the neck broke, would it collapse to a single body with faster rotation, or would it become two bodies orbiting a mutual center? And how would the sketchy "solid" material of the comet be affected by a collision between the two bodies?

        • Marco says:

          The point is that with just a few key assumptions about the integrity of the individual lobes, and their hard brittle nature, the conservation of angular momentum individually and in sum, and the assumption that kinetic energy is only added by gravitation and tidal forces, and taken away by friction, the resulting behaviour of the lobes can be roughly worked out.
          The lobes are rotating at less than mutual orbital velocity, so will not orbit each other without touching. I think the smaller lobe would roll down the broken neck and then would have a tendency to roll around the larger lobe rather than stick to it at another point. The friction won't slow down the rolling momentum it picks up. Any angular momentum lost from one lobe (by friction where it touches) will be passed to the other lobe. Thus the tendency would be for the smaller lobe to roll around the larger lobe, but almost certainly, the impact would be quite catastrophic.

          • Jim Robertson says:

            I think it would be fair to estimate that the angular momentum would also be passed to dust and chunks ejected from the contact points, even at such a low level of gravitational bonding. There isn't much attraction to keep the chunks corralled.

            If it's rolling contact (and of course an orbit would require an increase in angular momentum -- spin-up from gas jets?), I would expect the rolling activity to come to a stop at some low point between the lobes. With a big splash, or multiple splashes, of ejected material, and a great bloom in the coma.

        • Gerald says:

          At the current state it would become a contact binary, despite some spin-up. The collapse would be on the cm/s scale, hence no big challenge for the components to keep their shape.
          But it wouldn't be quite arbitrary. If there would be too much mass loss at the neck; centrifugal force would overcome gravity at some point, assuming either constant angular momentum, or constant angular velocity.

          • Marco says:

            What force would stop the lobes rotating independently? Ie. One lobe rolling on the other? The outside of the lobes would want to be going faster than the Middle.

  • Gerald says:

    Interesting option you are describing, kind of an n-th generation neck.

    • logan says:

      Like it. Fits nicely to bigger stages of comet formation.

      No material nor conditions down here as to think of re-fusion. In the best case will get a [temporal] binary.

      • logan says:

        Tend to agree with Marco, it will be a multi-fracture event. It will be a great show if Rosetta still watching! 🙂

Comments are closed.