The three faces of Rosetta’s comet

What a difference a week can make.

Even in the six days since the last image, the shape of comet 67P/Churyumov-Gerasimenko is becoming much more apparent, although still heavily pixelated.

Comet 67P/Churyumov-Gerasimenko on 4 July 2014. Credits:  ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Comet 67P/Churyumov-Gerasimenko on 4 July 2014. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

This sequence of three images are separated by 4 hours, and were taken on 4 July by the narrow angle camera of Rosetta’s scientific imaging system, OSIRIS. At this time, 37 000 km lay between the spacecraft and the comet, similar to the altitude at which geostationary satellites orbit Earth.

At this distance the comet covers an area of about 30 pixels in the narrow angle camera, with each pixel roughly equivalent to about 0.7 km.

The comet rotates with a period of about 12.4 hours. The image on the left is the first in the sequence, the middle around four hours later, and the right-hand one another four hours later. The small ‘lobe’ seen at the bottom of the first image is seen on the right in the second image, and at the top in the third.

It is not yet clear in which direction the rotation axis is pointing with respect to Rosetta, but the comet obviously has an irregular shape. Previous estimates suggested dimensions of 3 x 4 x 5 km, but we are now getting a more direct view.

But will it turn out to be long and skinny like comet Borrelly or Hartley 2, more rounded and lumpy, like Tempel-1 or Wild-2, or maybe somewhere in between, like Halley?

Let’s see what clues are revealed in the coming week.

Editor’s note: Some people immediately think of potatoes when they see a comet’s surface; but at the moment I’m seeing a broad bean or a kidney! What do you see?



  • Andrew R Brown says:

    Very interesting Emily.

    Looks like my idea of a concavity is looking plausible.

    Already although still pixellated, a definite shape is showing. Perhaps the next release may start to show surface features.

  • Tim Brew says:

    At this point the comet looks to be a possible contact binary.

  • serge says:

    Humm… it’s becoming good :-).
    Thanks for sharing this pic.
    I cant wait the next one(s) :D.

  • Andrew R Brown says:

    Would it be possible to upload tomorrow’s image when it is returned to Earth?

    This is getting very interesting.

  • Andrew R Brown says:

    It is Serge, I agree 100% 🙂

  • Michael Wiggins says:

    The fact that the comet has an apparent rotational rate of half a day says (to me, at least) that getting the lander on the comet may now be much easier to accomplish. True, all peril has not been removed, but this is far better than trying to get the lander on a rock spinning once per hour.

    Keep the data coming! There’s a lot of us scientist wannabe’s that enjoy the thrill of discovery as much as the real scientists do. And we can’t wait for more!

    • Andrew R Brown says:

      I wonder? That appears to be quite a ‘snout’ for want of a better word.

      Maybe a contact offset binary (not end on but towards the end on one side).

      Perhaps a much smaller version shape wise of Main Belt Asteroid 951 Gaspra seen by the Jupiter bound Galileo Spacecraft, but with a larger concavity?

      • Michael Wiggins says:


        If what you say about the comet possibly being a contact offset binary is true, do you think there a possibility that the comet has “inside” LaGrange points that might be exploited?

        • Andrew R Brown says:

          Hi Michael,

          May well do. If true than it is likely the main part of the nucleus is not of uniform density as any moonlet of the nucleus would ‘land’ on the part with the strongest gravity.

          If indeed a former moonlet, it will make the choice of landing Philae more difficult as the two bits could be quite different as in the case of Comet 103P/Hartley , seen by the Deep Impact Spacecraft where the smaller lobe had much larger boulders than the larger lobe which appeared smoother with fewer boulders.

          The same was seen with Asteroid 4179 Toutatis by the Chang’e 2 spacecraft.

          It may not be a former moon at all, rather the nucleus is a shattered splinter of a once larger body.

          I think we will have sharp enough imagery, possibly in the next release to be sure.

          Hope to get to see some surface detail too.

  • kees m says:

    how about a tweet in wich you compare your math models with the pictures through the coming weeks.?? Very interesting subject and maybe a word about gravity shifting in space by its irregular spave???

  • kees m says:

    form sorry

  • Philippe says:

    Clearly, this must be a German Brezel, hulled in and over-baked with yummy Cheeeese! :-)))

  • Wolfgang says:

    No coma or tail.
    Is this a strictly clean operation ?

    • Andrew R Brown says:

      The nucleus is far brighter than either the coma or tail so a much shorter exposure is used, hence the nucleus is not ‘burnt out’ in the images through over exposure, hence the black background of space.

      Also the area shown is tiny, so there would not be too much to see anyway.

      • Andrew R Brown says:

        P.S using the OSIRIS WAC with longer exposures will show more of the coma and tail.

        At the moment and rightly so, the attention is on the nucleus, it’s shape, rotational direction, rotational period, rotational orientation, the geology and surface features.

  • tomduf says:

    Rosetta is an amazing mission, but you can’t imagine how painful it is to wait your pictures ! The last one was taken 9 days ago.

    Why don’t you open a streaming website with raw images as other missions do, like Cassini ?

    You must have hundred of pictures, please share every pixel of knowledge with the whole world 😉

  • Prof Harvey Rutt says:

    Andrew. I’m not particularly familiar with comet dynamics. You seem to imply the comet may once have been a binary, a main body and an ‘moon let’, now fused. If I’ve understood that correctly, wouldn’t it be extremely unstable? Surely even very slight perturbations from other bodies would destroy such asystem?

    • Marco Parigi says:

      Yes. Even perturbations from the out gassing jets of the comet would destabilise a binary system. More likely is a lobe or lobes similar to Borrelly or Hartley , but otherwise a single comet nucleus..

      • Andrew R Brown says:

        I agree that this would not be the most stable of situations.

        Comet 103P/Hartley is certainly a contact binary as is the Asteroid 4179 Toutatis.

        A contact binary or even a contact trinary cannot be entirely ruled out at this stage.

        I am not sure the jets would have enough power to pull a contact binary apart.

        It is most likely a single nucleus, until we get to see closer images, it is largely guesswork.

  • Pete Williams says:

    I’m trying to come up with a smart arse or jocular comment…however these have all been taken so I will content myself with a WOW statement!
    AND it really is wow, all that way and still ‘not there yet’!
    ESA and Rosetta, inspiring the impatient hell out of humanity!

  • daniel broux says:

    when can we expect the next pics of the comet ?

  • JonatanPL says:

    Is Rosetta dead? i know making pictures of closing to rosetta isnt its priority but WE are anxious to see it!!! More updates more pictures. We want to live and discover too 😀 (I am European so paying Taxes for it :P) Dont leave all the science for youreselfes 😀

    • Andreas says:

      All Rosetta science instrument data have a proprietary period of 6 months, after which they will be publicly available in our archives, …

      That is to say: Principal investigators will want to write their articles before the raw data gets available to the public.

      BTW: Rosetta is currently preparing for the next orbit correction maneuver. That last science timeslot ended 13/Jun at a distance of roughly 13600km.

      • Marco says:

        BUT, as correctly underlined by JonatanPL, we are the taxpayers that made possible the mission and, I think, we have the right to see some preview picture in (almost) real time; I am sure that such activity would greatly increase public involvement and will benefit ESA in the future, through policy choices!
        I am not asking to deliver all scientific data in real time, only some jpeg images! NASA should teach you something about this…

        • Andreas says:

          I agree. Do avoid misunderstandings, I am not affiliated with ESA or any other organisation. I am desperately searching for information like anyone else. Just wanted to explain, it is probably not negligence of the public relations team …

  • leodp says:

    Hey, BBC has some updated images which cannot be found on Rosetta blog yet.
    When do you update?

  • emily says:

    Dear all, yesterday’s preview was unscheduled, which is why you did not see it first here on the blog. We’ll be putting out even newer images and a movie of comet 67P/C-G, along with scientific commentary, in tomorrow’s planned weekly image release.

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