The dual personality of comet 67P/C-G

Comet 67P/C-G imaged on 14 July 2014 from a distance of approximately 12 000 km. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Comet 67P/C-G imaged on 14 July 2014 from a distance of approximately 12 000 km.

This week’s images of comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape. We had hints of that in last week’s images and in the unscheduled previews that were seen a few days ago, and in that short time it has become clear that this is no ordinary comet. Like its name, it seems that comet 67P/C-G is in two parts.

What the spacecraft is actually seeing is the pixelated image shown at right, which was taken by Rosetta’s OSIRIS narrow angle camera on 14 July from a distance of 12 000 km.

A second image and a movie show the comet after the image has been processed. The technique used, called “sub-sampling by interpolation”, only acts to remove the pixelisation and make a smoother image, and it is important to note that the comet’s surface features won’t be as smooth as the processing implies. The surface texture has yet to be resolved simply because we are still too far away; any apparent brighter or darker regions may turn out to be false interpretations at this early stage.

But the movie, which uses a sequence of 36 interpolated images each separated by 20 minutes, certainly provides a truly stunning 360-degree preview of the overall complex shape of the comet. Regardless of surface texture, we can certainly see an irregular shaped world shining through. Indeed, some people have already likened the shape to a duck, with a distinct body and head.

Although less obvious in the ‘real’ image, the movie of interpolated images supports the presence of two definite components. One segment seems to be rather elongated, while the other appears more bulbous.

Dual objects like this – known as ‘contact binaries’ in comet and asteroid terminology – are not uncommon.

Indeed, comet 8P/Tuttle is thought to be such a contact binary; radio imaging by the ground-based Arecibo telescope in Puerto Rico in 2008 suggested that it comprises two sphere-like objects. Meanwhile, the bone-shaped comet 103P/Hartley 2, imaged during NASA’s EPOXI flyby in 2011, revealed a comet with two distinct halves separated by a smooth region. In addition, observations of asteroid 25143 Itokawa by JAXA’s Hayabusa mission, combined with ground-based data, suggest an asteroid comprising two sections of highly contrasting densities.

Rotating view of comet 67P/C-G on 14 July 2014. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Rotating view of comet 67P/C-G on 14 July 2014.

Is Rosetta en-route to rendezvous with a similar breed of comet? The scientific rewards of studying such a comet would be high, as a number of possibilities exist as to how they form.

One popular theory is that such an object could arise when two comets – even two compositionally distinct comets – melded together under a low velocity collision during the Solar System’s formation billions of years ago, when small building blocks of rocky and icy debris coalesced to eventually create planets. Perhaps comet 67P/C-G will provide a unique record of the physical processes of accretion.

Or maybe it is the other way around – that is, a single comet could be tugged into a curious shape by the strong gravitational pull of a large object like Jupiter or the Sun; after all, comets are rubble piles with weak internal strength as directly witnessed in the fragmentation of comet Shoemaker-Levy 9 and the subsequent impacts into Jupiter, 20 years ago this week. Perhaps the two parts of comet 67P/C-G will one day separate completely.

Comet 67P/C-G on 14 July 2014 – processed view. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Comet 67P/C-G on 14 July 2014 – processed view. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

On the other hand, perhaps comet 67P/C-G may have once been a much rounder object that became highly asymmetric thanks to ice evaporation. This could have happened when the comet first entered the Solar System from the Kuiper Belt, or on subsequent orbits around the Sun.

One could also speculate that the striking dichotomy of the comet’s morphology is the result of a near catastrophic impact event that ripped out one side of the comet. Similarly, it is not unreasonable to think that a large outburst event may have weakened one side of the comet so much that it simply gave away, crumbling into space.

But, while the interpolated images are certainly brilliant, we need to be closer still to see a better three-dimensional view – not to mention to perform a spectroscopic analysis to determine the comet’s composition – in order to draw robust scientific conclusions about this exciting comet.

Rosetta Mission Manager Fred Jansen comments: “We currently see images that suggest a rather complex cometary shape, but there is still a lot that we need to learn before jumping to conclusions. Not only in terms of what this means for comet science in general, but also regarding our planning for science observations, and the operational aspects of the mission such as orbiting and landing.

“We will need to perform detailed analyses and modelling of the shape of the comet to determine how best we can fly around such a uniquely shaped body, taking into account flight control and astrodynamics, the science requirements of the mission, and the landing-related elements like landing site analysis and lander-to-orbiter visibility. But, with fewer than 10 000 km to go before the 6 August rendezvous, our open questions will soon be answered.”





  • Andrew R Brown. says:

    WOW, looks like there is an impact crater on the end of the smaller lobe.

    The comet is a prograde rotator after all.

    • emily says:

      Hi Andrew, remember that the surface texture has yet to be resolved – any apparent brighter or darker regions in the processed view may turn out to be false interpretations. Let’s see…!

      • Andrew R Brown says:

        Indeed, I still see a crater there, but as you say it could be a shadow or something else instead.

        Still a great rotation movie though. 😀

        The two parts are of very different shapes, will be interesting to see when Rosetta draws closer if the surface texture is similar on both ‘pieces’ or they are even the same colour.

        I would expect at the next image release we will be sure.

    • Andreas says:

      Hmm, SPICE-data in the planetary science archive still tells, that it should spin the other way around (RA=220, DEC=-70 with prime meridian moving 679 deg / day). This data is more than two years old, but I could not find a recent file.

      The way the spin is shown now in the published animation, it makes more sense that it could be induced by capture.

      • Kim Gram says:

        “Is it a potato? Is it a rubber duck? It’s definitely not Superman! ”

        It probably isen’t Einstein.

  • Ronaldo says:

    Have you figured out how to land in the conditions that are showing up?

    • emily says:

      Hi Ronaldo, it’s too early to tell – the team need a much more detailed view of the surface/structure etc (see Fred’s quote).

  • David P says:

    Wow, really cool, and thanks for the different possible scenarios that could lead up to a shape like that (though I can’t immediately parse “a large outburst event” ).

    It shall be supremely interesting to actually see what happens when it gets closer to the sun.

    • emily says:

      Thanks David, it’s certainly interesting to consider different possibilities, even if some of them soon turn out to be wrong 🙂

      • Marco Parigi says:

        Yes. Thanks for the different possibilities. I was not happy with the speculation that came with the leaked pictures that it “had” to have been from a low velocity collision. As you say, some should be ruled out soon enough!

  • Arthur says:

    Be vigilant and watch out for the monster that has lost the pacifier !

  • Dave Harvey says:

    How odd that the commentator is saying what they WILL see in the future, pretending that he hasn’t already seen the data which is being kept hidden from us “plebs”. We all expect such double-speak from politicians, but NOT from scientists!

    • Mark McCaughrean says:

      That’s simply not the case: we have not seen any more images. Emily’s just using a turn of phrase, knowing as we all do that Rosetta is getting closer to 67P/C-G, so we will see more detail when the next images are taken.

      • armchair explorer says:

        We can’t know when OSIRIS imaging seasons are scheduled or when new images are downloaded from Rosetta, and thus whether project scientists have already better images of 67P available.

        • Mark McCaughrean says:

          Understood, but then I think it’s equally unreasonable for the previous poster to make very strong (and critical) assumptions about what we have done and what we have seen “in secret”.

          • armchair explorer says:

            I agree, but it is fair to say that one reason for the occurrence of such critical assumptions lies in the limited information policy about spacecraft operations and data gathering.

          • V.Losada says:

            @Mark McCaughrean:
            I’m sorry, but it’s not the same at all. The problem you have at this moment is the post you and others have signed in (“Access to Rosetta Data”), stating a so called “proprietary period” (up to SIX MONTHS!!!) for the data of the mission.

            So far, I have not seen any statement from your side backtracking on that. That’s why we have every right to think that the “proprietary period” policy remains in effect and that indeed you have pictures that are not shared with the European taxpayers who have funded this mission, and are funding your jobs in ESA.

            It would be very easy for you to recover our confidence: You only need to do a post similar to the previous one, stating that the “proprietary period” has been a mistake, and that it has been removed. Until then, you will understand that it is very difficult for us to believe in you.

  • Phil says:

    Any chance we can download the unprocessed images that made up that video?

    • Kim Gram says:


      Quote from the article :

      “A second image and a movie show the comet after the image has been processed. The technique used, called “sub-sampling by interpolation”, only acts to remove the pixelisation and make a smoother image”

      It could be a good idea to publish the data ( from before that processing ), now,

      one reason is: Many amateurs would repeat the processing,
      and if ( though higly unlikely )
      the ESA hardware or software made errors in the calculations, some would then probably detect it now.

  • John says:

    Fascinating! Best of luck to the team.

  • Paolo Lombardi says:

    Are those photo taken with the Navigation Camera?

    • Andrew R Brown says:

      No, it was with the OSIRIS Narrow Angle Camera. The Navigation Camera would only show a large dot due to it’s much wider angle view.

      When close in the Navigation Camera and the OSIRIS Wide Angle Camera will provide some fantastic ‘global’ and regional images whilst the OSIRIS Narrow Angle Camera provides close ups of interesting features.

  • cosmictwang says:

    Is there any compositional info on these guys? What kind of pressures would a collision like this involve?

  • Pablo says:

    Would that irregular shape on rotation become a problem to select a site for lander? would be possible to follow the rotation before approaching? The manouver definition will be an exciiting task.

    • Andrew R Brown says:

      Hi Pablo,

      Not really. The Rosetta Mission scientists and engineers always designed the Philae Lander to land on a rotating irregularly shaped, rotating object.

      The rotation of the nucleus of Comet 67P/Churyumov–Gerasimenko, is reasonably slow, completing a rotation on it’s axis approx every 12 hours, 36 minutes so rotational speed will not pose a significant problem.

      The biggest issue will be scientific. If indeed the two ‘pieces’ are two different comet nucleuses, then which one to land Philae?

      If indeed the same shape is two ‘pieces’ from the same object that came back together or indeed the weird shape is indeed from ablation, it will be easier.

      If there is a reasonably deep impact crater, that would probably be the best place as that would provide a natural borehole to a deeper level and the icy material would have had less time being exposed to space with less modification from the Sun and or dust.

      We’ll see.

  • Nigel says:

    Truly amazing stuff, space is exciting again!

  • Dean Brown says:

    Wow this is really exciting – we’ve never gone to another body like this before, it’s always shoot there and then land and then show us a picture of the surface. Now we are gradually creeping up onto this one, seeing changes every few days, I love this new approach!

  • Jani says:

    Intriguing! And this is just the start of exploration! I can hardly wait for the radio experiment to probe the innards of the comet.

    I wish best for the scientific and operation teams! Happy times ahead…

  • Tom says:

    Thanks this is spectaculair! Unfortunatly still a 3 day delay; can you go to a 1 hour delay from now on?

    The many well writen comments on the “Access to Rosetta data” statement need folow up. This is as crittical for the succes of the mission as all the other work!

    Share with the public and make history!

    • Michael Khan says:

      I wonder whether people who seriously expect the publication of processed and meaningful commented images within one hour have any hands-on experience with scientific work at all. Such demands show no understanding of the amount of work that goes even into seemingly simple images such as the above.

      There is no such thing as “instant science”. I am not saying that ESA,, or more specifically, the investigators, because after all it is they who own the publication rights the the data gathered by their instrument and it is they who are best qualified to process and interpret their material, could not be a bit more forthcoming. But they can’t work wonders either. Things require the time that they require.

      The outreach work for the Rosetta mission has been, if anything, fast. In other ESA missions, such as Mars Express and SMART-1, it has happened that entire months passed with no outreach material reaching the public. Even so, there is always scope for improvement.

      That said, unreasonable expectations are not exactly helpful.

      • armchair explorer says:

        You missed the point.

      • Dave Harvey says:

        Whilst “processed and meaningful commented” images have their place, and of course do take time, that is not the case for the “raw” images, which could be put on the web as easily as they can be placed on the internal servers, and which would be gratefully received by many people, just as the NASA ones are. In fact, such an approach could actually improve the scientific aspects of the project, by freeing the project scientists to concentrate on the “real” science, leaving the production of pretty pictures to others, who may actually have more skill in that area.

  • Gianfranco D'Elia says:

    Finalmente incontriamo un oggetto interessante da studiare da vicino e su cui atterrare!

  • Pete Williams says:

    What would be the protocol IF, when we come to the lander part of the mission, we find that there is somebody already there and doing science. 😉
    Well done to ESA for this achievement and the best is yet to come. All that way, humankind truly reaching out into space.

  • Andrew R Brown says:

    Hi Emily,

    Something else has occurred to me (get the flags, bunting and fireworks out, as it does not happen ofter) :D.

    The Comet 67P/Churyumov–Gerasimenko Jupiter encounters in 1840 and 1959.

    Firstly what where the minimum distances, perijove to Jupiter in each encounter?

    Secondly, could sulphur from the huge volcanically active moon Io contaminate the surface of the comet or was Comet 67P/Churyumov–Gerasimenko too far away for that to be an issue?

    Thirdly, was perijove close enough to contribute to the weird shape?

    • emily says:

      Hi Andrew, I’ve been looking for some info for you about the aphelion distances and have this, from C. Tubiana, 2008: The last encounter in February 1959 occurred at a distance of only 0.0518 AU and produced a drastic change in the orbit of 67P/C-G. In fact its perihelion distance dropped from 2.76 AU to 1.29 AU, the eccentricity of the orbit increased from 0.36 to 0.63, the inclination decreased from 23.15º to 7.13º and the orbital period of 67P/C-G shortened from 9.00 y to 6.55 y (Belyaev et al. 1986). It is speculated that this drastic change may have triggered the activity of the comet, which most likely led to its discovery in 1969.

      • Andrew R Brown says:

        Thank You very much Emily.

        0.0518 AU. 7.77 million KM .That’s only about a third of the distance between Jupiter and the outlying Pasiphae and Carme family retrograding moons, so yes that would have altered 67P/C-G’s orbit enormously

        So really 67P/C-G has not had many closer perihelia than most others, makes me think that the contact binary nature of the nucleus is indeed two objects ‘fused’ together, whether from the same parent body or indeed two separate comets welded together long ago when 67P/C-G was still resident in the Kuiper Belt rather than ablated to that weird shape..

        This is getting more and more interesting by the day.

        Please lets us know how the final FAT burn geos tomorrow 🙂

        Andrew R Brown.

  • Andrew R Brown says:

    P.S I apologize for me poor use of words and English over the weekend at times, as I have been rather tired, I know what I want to say, but it can be difficult at times to put into words.

    I am a very high functioning Autistic with a supposedly unusually high IQ, but I do get extremely mentally tired at times.

    I am aware that users and moderators of the ESA and NASA boards are well educated people with likely well above intelligence and I do try not to lower the quality.

    Just to say that some ideas I have submitted to NASA regarding the MRO (HiRISE in particular), MSL Curiosity and Mercury MESSENGER missions ( I may be close to assisting in the discovery of a potentially active volcanic vent on Mercury) have been carried out.

    This is the very first ESA mission that I have had a real sense of participation with, particularly with asteroid 21 Lutetia pass.

    I am not employed by either NASA or ESA, I live in the UK, Ashford in Kent, but have been invited by NASA to attend launches and events.

    Just needed to explain myself if other contributors and / or moderators think I am a little strange.



  • hansbroer says:

    I think you’re right Andrew, Not only de light-dark distribution in de position right-under suggests a crater, but also the slope visible in the left-upside position. Nice to speculate on it with this little though congruent details. Hans Broer

  • dan ioan says:

    6 days old pictures now..; I’ve read all your reasons none makes sense for this unless we struck gold. If its a PR strategy and you are keeping images for 6th of August rendezvous and media press conference, i say fire them all because I’m of to nasa site to see the 20+ new pictures from mars they post everyday.
    No offense, i know its not the responsibility of you, those taking care of the blog and reading all this, but i’m urging you to push up the message up your ranks, because this is ridiculous. Thanks

  • Walter says:

    What is Rosette’s approach velocity? Compared to other comet flyby’s, it must be closing in at a speed comparable to a lory in low gear.

    • emily says:

      Hi Walter, the relative speed between Rosetta and the comet will indeed be very low when rendezvous occurs – about 1m/s, equivalent to walking pace.

  • Martin Lane says:

    So will the two parts be called Churyumov and Gerasimenko and who gets the bigger one?

  • Thomas from Berlin says:

    great pictures and films! Well done ESA

    I wonder how fast the rotational speed of the Comet is. Would it be as fast as on the film, I immagine landing becoming difficult. However, as I write it might be slow enough.

    Does anyone know?

  • Ivo says:

    Přistání Philae bude směřovat do blízkosti středu těžiště komety; otázka:
    jak robota Philae ‘rychle’ k těžišti dostat, aby ho kometa neodpálkovala?
    EU, /state CR/, matér;

  • kejahos says:

    Přistání Philae bude směřovat do blízkosti středu těžiště komety; otázka:
    jak robota Philae ‘rychle’ k těžišti dostat, aby ho kometa neodpálkovala?
    EU, /state CR/, matér;

    • kejahos says:

      Landing Philae will go near the center of gravity of the comet; Question:
      how the robot Philae ‘fast’ center of gravity to get to him neodpálkovala comet?
      EU / state CR /, amateur;

  • dan ioan says:

    8 days with no pictures, not to mention last set was first leaked and only after another 2 days officially published. When are we to expect next set of pictures?(if so at all)

    • emily says:

      Hi dan,
      As mentioned in several other posts, releases of OSIRIS image(s) are running on a weekly schedule – the next one is due tomorrow (Thursday).

      • Philippe says:

        Patience, patience…!
        C’est ce que je répète tous les jours à mes filles.

        PS. Un peu de français dans cet océan anglophone, ça change, non ?

  • Andrew R Brown. says:

    Excellent news, the final FAT burn was executed flawlessly. 🙂

    The work is all but done now, the CAT burns are very minor.

  • emily says:

    In response to V.Losada’s comment above, from Mark McCaughrean:

    “At the time I wrote my earlier comment, no new OSIRIS images had been taken, so independent of the proprietary period, there were no more to share. It’s important to realise that Rosetta’s cameras are not permanently “on”, streaming data back to Earth, but only take data occasionally as part of a coordinated operational plan. Rosetta is far too far away from Earth to allow any kind of continuous image streaming: the bandwidth is way too low.

    But since my comment, more recent images have now been taken and were released yesterday.

    Our earlier post explains the basis for the proprietary period for Rosetta, as is standard practice in almost all scientific experiments worldwide. Some images are being made available by the OSIRIS team much earlier, however, recognising the great public interest in the mission.”

  • cXnJohn says:

    Looks to me like 2 smaller comets collided together to make one big one, the way they rotate also looks like the smaller of the 2 collided where it resides now and knocked the bigger one it to its combined current spin.

    Im talking from the newer higher resolution images that are being published now.

  • Raghuram says:

    Could you tell me what is angle between rotation axis of comet and perpendicular ecliptic plane??

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