Philae’s descent: The director’s cut

This blog post is contributed by Mark McCaughrean, Senior Science Advisor at ESA.

On 30 July, the first papers covering the scientific results obtained by Philae on the surface of Comet 67P/Churyumov-Gerasimenko were published in Science magazine. On that occasion, we released a number of images taken by Philae on 12 November 2014, including a sequence of seven taken by the ROLIS downward-looking camera towards the end of the descent to the lander's first touchdown point at Agilkia, previously known as Site J. (As is now well-known, Philae rebounded after briefly touching down at Agilkia, eventually coming to rest at a site called Abydos.)

Now, to mark the first anniversary of the selection of Site J as the target for Philae, we are releasing a “special edition” version of that ROLIS image sequence. The seven still images, each spaced by 10 seconds, have been interpolated in time to create a movie that shows Philae's descent between 67 metres and just 9 metres above the surface in real-time, taking just under 1 minute. The movie ends at that point, as there are no further images in the sequence: Philae had touched down at Agilkia before another 10 seconds had passed.

Having worked with Jakub Knapik, visual effects supervisor at Platige Image, Warsaw on our short sci-fi film, "Ambition", we were delighted when he took those seven ROLIS images and used state-of-the-art visual effects tools to interpolate between the images to create this movie sequence.

(For the technically-curious among you, Jakub used the VFX compositor NUKE from The Foundry to re-project the original set of seven images in 3D, then rendered an interpolated sequence using a tracked 3D camera that mimicked the path of Philae during its descent.)

If you look closely at the original seven ROLIS images you will notice that there were data drop-outs in some of them: Jakub was able to fill these using data from previous or following images, apart from at the beginning of the movie, where some minor cloning of data was needed to fill some holes. Also, Jakub masked out the parts of Philae seen at top-left and top-right in the images before interpolating, replacing them afterwards.

The result is a beautiful, almost hypnotic movie, showing just what Philae would have witnessed as it drifted slowly down onto Comet 67P/C-G at walking pace on 12 November. We have added some caption material, although the times, distances, and resolutions shown are not necessarily exactly in sync with the images.

We also felt that this movie deserved a soundtrack, and are very grateful that Jem Godfrey of Frost* has allowed us to use the instrumental version of “Saline” from their 2008 album, “Experiments in Mass Appeal” for this purpose.

To be clear, there are no instruments on Philae or Rosetta capable of taking true real-time video, and in any case, it would be extremely difficult to downlink such a large volume of data over the huge distance between 67P/C-G and the Earth.

So, we want to stress again that the raw data making up this movie are the same seven ROLIS images already released on 30 July and for any serious analysis, you should refer to them.

But we think Jakub's movie version gives a much more visceral impression of the first ever soft-landing on a comet and are happy to share it with you. Enjoy!


Original descent sequence images: ESA/Rosetta/Philae/ROLIS/DLR, Stefano Mottola
Sequence interpolation and editing: Jakub Knapik, Platige Image
Music: “Saline” (instrumental version), from “Experiments in Mass Appeal”, Frost*/Jem Godfrey
Overall movie editing: Sarah Poletti and Marc Thiebaut (ATG/medialab for ESA)




  • Sovereign Slave says:

    Very nice video, thanks for sharing. And I know this is apparently unscientific, but it still impresses on me how, no matter the distance, whether up close or far away, the comet still looks exactly like hard rock and dirt/dust. Show this video to anyone unaware of where it came from, and they would say rock and dirt. Everyone knows what rock and dirt and dust look like, and that’s exactly what these pictures look like. In fact, in all the hundreds to thousands of pictures now taken of P67, has there been even ONE picture that clearly, unequivocally shows frozen volatiles mixed with dust, or ice, or anything else that does not resemble some form of rock, dirt, or dust? And yes, no need to repeat the “we can’t trust our eyes” argument, but come on, shouldn’t this be considered at least a little problematic to standard theory?

    • Harvey says:

      470kg/m^3 is an even bigger problem for a theory that says it's solid rock an ice, than a casual similarity to those materials is for standard theories'.
      That value must now be established by literally hundreds, probably thousands of measurements of Rosetta's and Philae's trajectories.

      What would such a picture look like? From standing on a good many dusty glaciers, it could look just like this.

    • Bill Davis says:

      You have your eyes open. I have noticed same. It would be interesting to hear the comments on detection of water and other volatiles put in terms of upper limits on their percentage of bulk composition. Also there is mineral detection capability and we haven't yet, I think, heard anything about the highly processed minerals that I expect to be in found, for instance olivine which was found by the Stardust comet probe sample return. Also recall the results from Deep Impact - Jessica Sunshine as lead author in a paper noted in conclusion a maximum of .5 per cent of the Tempel 2 surface had any possible ice.

      • ianw16 says:

        @Bill Davis
        Well, if you read that paper, you would also have noticed that what came out of the comet when it was struck by DI was H2O. Unequivocally. Water. Where did it come from?

    • Mark McCaughrean says:

      A few things to consider here:

      (1) Along with the great majority of images that we've published, the greyscale in the ROLIS images that went to make up this film has been stretched to maximise the dynamic range. In reality, most of the comet is very dark, albedo around 6%.

      So, any assertions along the lines of "it looks like X, therefore it is X" do need to be made with great caution.

      (2) That said, we have indeed published images showing patches of brighter, blue-ish patches on the surface, strongly suggestive of water ice.

      For example:

      (3) The images linked to above date back to autumn last year, before activity increased as the comet approached the Sun.

      The small patches of revealed water ice are thought to have lasted since the previous perihelion, but much more should be seen as the images being taken now are analysed by the science teams.

      (4) You don't need much dust and organic material mixed in with volatiles to turn the whole mess dark. Especially when the surface layers are heated and the volatiles sublime off, leaving a dark layer.

      Whether that layer insulates or promotes melting is an interesting question, at least in the Earth context when you look at snowpiles collected in winter that survive deep into summer, e.g.

    • Sovereign Slave says:

      All good sounding arguments, but still, it’s fascinating to me how belief dictates what we think we see. My eyes tell me that I’m seeing rock, dirt and dust in all those pictures, and so that’s what I believe, contrary to what the currently available science is apparently suggesting. For most others, based on the science, they believe it’s some form of dirty ice-ish matter, so their belief tells their eyes that that’s what they’re seeing, and that it’s not rock at all (though they seem ready enough to believe that they are seeing the dust as dust). I can’t seem to shake the conviction that the visual evidence of my eyes is right, and unlike the others, my faith in the interpretations and reliability of the available science to date is not nearly strong enough to override that conviction. Perhaps when the asserted “whats” can be better supported by much better detailed and believable answers to the incredibly sketchy “hows,” I’ll be better persuaded.

      • Harvey says:

        I take your point - but for me it is different.

        I do not 'see' either thing; because the evidence is not there to support it.

        I'm always looking for consistency with the other data; the density, the out gassing species, VIRTIS and MIRO results etc.

        If I only had the picture, but knew it was from a comet, I wouldn't be prepared to say almost anything about what it was; the information just isn't there; well it's not liquid; there is an indication of two morphologies and scale lengths, bigger fragments and possibly a finer grain material; what more can I say about what the material is?

        The difference is probably just one of long experience. It's amazing what you can find in SEM pictures for example - until you recall the scale and contrast mechanisms!

      • Gerald says:

        Most of the surface material of the comet is refactory material fallen back from jets and outbursts, or other remnants, the ices of which are mostly sublimated already.
        You may take a look at carbonaceous chondrites:
        They look a little like rock, and they are likely to ressemble some of the comet surface refactory material.

        This material covers the ice/dust mix of the subsurface.
        Although it's hard to say how think this layer is.
        A few millimeters are sufficient to hide the ices.

    • logan says:

      Explicitly this point of the comet indeed looks like you say. Even at this close approach. As Robin says, quite probably this is very metamorphic material. All kinds of surfacing cycles, erosion, space weathering later.

      • logan says:

        Abydos looks to me like a scene at bottom of the mid atlantic dorsal.

        • logan says:

          If going to believe my eyes, then lots of liquid transparent water around Philae, at Abydos.

  • Dave says:

    Sorry Harvey,
    But sovereign slave and Bill Davis make a good point. Also if you have another look at the picture from Philae that were recently posted, your senses scream rock and aggregate.
    Maybe the ices are still playing hide and seek. By now though we might of expected more evidence. The faint evidence of ice found at the surface a few months ago looks more like a transient patch of condensate falling back to the comet freezing to the surface in the shade. Then maybe sublimating at the next sunrise. I am still listening to your cautions but it's getting more difficult.
    Are you still sure the landing site in the vid is crumbs of dirty ice and dirty ice boulders?

    • Harvey says:

      Given 470kg/m^3, and the comet degassing huge amounts of water (300kg/sec mentioned recently) and probably even more CO and CO2 yes.
      The only credible source of those compounds is ices; claims they originate from the solar wind and combustion are frankly nonsensical, without any base in scientific fact.
      The ices are also low density, making achievement of the low overall density easier without extreme porosity.
      You can't tell what something is, especially an utterly unfamiliar material processed by utterly unfamiliar conditions, just by looking at it. It takes a micron of organic gunk to hide ice.
      Furthermore as I said it doesn't look that different to plenty of bits of high altitude glacier I've climbed on! Though, for the reasons given, I place little value in that comparison.

    • ianw16 says:

      It might be what your senses are screaming, but there is zero scientific evidence to back it up!
      As mentioned, what Deep Impact excavated at Tempel 1 was H2O. This from a surface that showed no evidence of ice in that vicinity. The crater it left behind is of a size that is totally inconsistent with a rocky body.
      The gravity measurements at this and numerous other comets preclude it being rock.
      The discovery of H20 close to the surface (within a meter in Philae's case) shows that there is ice around, not far from the surface.
      The very energetic jets at Hartley 2 were spectrally resolved as being mainly CO2. Temperature maps were made of that comet, including the area from which the most energetic jets appeared. There were no anomalies.
      Pareidolia isn't science. Observation and measurement is science.

  • Neil Morrison says:

    Thank you ESA for a very fine montage of images blended together which indeed gave the feeling of floating down to touch the Comet. Putting all the technical arguments aside when the Dust settles a little bit in the closing stages of the mission it would be very helpfull for those of us who get involved with Public Outreach events to have a film on hand of the mission . Launch, first approach, descent, overflight and close ups of the pits etc and then the slow shut down as the Comet departs from the Sun. Such a film could be used not only to explain Comets , Meteors and other dusty phenomena. The Scouts and Cubs would lap it up.

  • Jason says:

    At 15:33:33 GMT
    Range 33.3 [m]eters from #67p landing site

    The surface appears sandy
    the rocks smooth and in the form of smooth dead corals
    the other features resemble small broken discarded 'engineered' items.

  • Alex says:


    There's been an interpolated version of the descent on YouTube for quite some time, I processed the images using Matlab and uploaded the results about a week after they were published.

    Here's a link:

    Although must say that I really liked Jakub's version and that he included the visible parts of the lander together with the video.

    • Mark McCaughrean says:

      Good to see, Alex: indeed, we were a little surprised that something like that hadn't surfaced already 🙂

      If I'm right, your movie "simply" zooms in on the seven images (you can see the change in resolution at the various boundaries), whereas Jakub's is actually rendered from a 3D model created from the original 7 images, maintaining a more constant resolution throughout.

      But it's all good stuff, and we're of course very happy to see the community engaging with the mission and its data: thanks again.

  • Dave says:

    Our senses are easily fooled I agree, especially here where not all the senses can operate, and we rely on a robot to provide some sense.
    I am still with your assertions
    But it is still possible to look for different scenarios. A low albedo does not mean it's not rock, especially that there seems to be a coating of various hydrocarbon substances every where. Also there are other reasons for low gravity, could be the interior does have big cavities in it. We have done our best to look through the comet, but we have not found the cavities that seem to be close to the surface that seem to cause the jets that switch on suddenly with a burst of debris. There must be many more scenarios that could describe of if we did a brain storm. However porous ice with unknown mechanisms for exploding sublimation, and drilling deep parallel pits must still be pole position.'

    • Harvey says:

      Broadly I guess we agree. The CONSERT data regarding cavities is extremely limited unfortunately.

      A model with rock and large cavities could reproduce the average density - although it's possible detailed trajectory data not yet analysed/published could tell us something about that. The black organic gunk means we simply don't see the base material, be it rock, ice or cream cheese 🙂

      But it has no way to explain the degassing CO, CO2 and molecular water. These make it pretty well a given that these compounds are present in quantity in the comet.
      The solar wind and combustion 'hypotheses' are scientifically untenable.
      An awful lot of brainstorming has been done, and so far the 'conventional' view is the only one that actually stands up.
      How it generates the terrain etc I really don't know; but I've still seen no remotely credible alternative to a porous ices/Rock/carbonaceous material mix. I'll happily dump it if something better comes along!

    • logan says:

      Hi Dave. ROSETTA will never go as far as to conclude what materials are not at 67P.

      But, little evolved or un-evolved accreted material at 67P, seems to my mind more like Robin's "cryo-rocks". Aerogel like, visually, but with a denser matrix:

  • logan says:

    Not far from what a real video would have brought to us 🙂 Thanks Jacob. Also to Mark, Karen and all of OutReach Team about bringing this delightful document to us.

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