CometWatch – 18 August

Rosetta navigation camera (NAVCAM) image taken on 18 August 2014 at a distance of about 84 km from comet 67P/C-G.

Full-frame NAVCAM image taken on 18 August 2014 from a distance of about 84 km from comet 67P/Churyumov-Gerasimenko. Credits: ESA/Rosetta/NAVCAM

Full-frame NAVCAM image taken on 18 August 2014 from a distance of about 84 km from comet 67P/Churyumov-Gerasimenko. Credits: ESA/Rosetta/NAVCAM

Comments

16 Comments

  • David Williams says:

    The topography just gets more and more interesting, as expected I suppose. Considering the micro gravity, it's strange how there appears to be cliff slides as pronounced as they seem to be, and what looks like spillage from the top crater to the left of that prominence.

  • Dave Higgins says:

    Another great picture, glad that we are a bit closer again. The small white outs arround the neck look like hot spots (I appricaite you may be adjusting the light in the picture) However these look very much what you might expect from an electrical process, Any ideas?
    Are you close enough yet to detect water?
    It seemds trhere was no water on Borrelly and wild 2.
    If its not on 67P, does that mean that the norm will be no ice for comets?

    • Allan Bell says:

      Borrelly had no surface ice, perhaps because it had sublimated away but it had ice beneath. http://www.jpl.nasa.gov/releases/2002/release_2002_80.html
      Once it heats up the water vapour presumably burst out from below.

      There was evidence of water on Wild 2 http://earthsky.org/space/evidence-for-liquid-water-on-the-surface-of-comet-wild-2

      What do mean by electrical process? This is not an electric universe reference, i hope.

      • Dr Stephen Rhodes says:

        Why does any suggestion that there may be charge separation at work in the universe bring a 'knee-jerk' response that amounts to little more than an appeal to authority and a cry of 'burn the heretic'?

        I always thought that the scientific method involved rather more than defending existing paradigms at all costs. Have we not learned the lessons of the epicycles created to defend the geocentric model of the universe.

      • Dave Higgins says:

        High Alan,
        I believe that the references you have quoted are some what inconclusive, and so would look for this mission to get into greater detail (early days yet)
        This Comet and the others we have looked at look like they have hard rock surfaces, that have some how been eroded,not loose conglomerations that have been impacted.
        The craters don't appear to conform to a normal shape of an impact, ie hexagonal shapes, flat floors and steep vertical sides to quote just a few anomalies.

        If the the comet is a loose mix of dust and ice , you might expect, if the large craters really are collision events, that the collisions might have smashed a loosely bound comet to pieces or for large objects to have lodged in the surface if there was a slow collision.However this is not what we see.
        If there is no ice on the surface and it is all rock, it is possible that all the surface ice has sublimated away. However if as you say, that the ice is beneath the surface, then any sublimation would exert a large pressure from the inside when sublimating, if this were to happen you might expect to see some sort of fissure or crack on the surface or other explosive release of pressure.
        If there once was water ice below the surface and it was seeping out by sublimation, would you expect to see the comet get more and more hollow with every pass round the sun?
        There are lots of unexplained features that don't seem to fit the accepted theory or any theory. With an open mind its great to have the opportunity look closely at the evidence to see how it all works. The mission is exploratory, so the fact things don't yet add up is exiting and hopefully will enhance our scientific horizons, but it will only do this if we question what we see.

        Regards

    • Ingo Althöfer says:

      67P seems to have lots of water. On August 06 it was told
      that around August 01, the comet lost about 2000 liters
      of water in each hour.

      • Dave Higgins says:

        this would only be true if what has been measured is water from sublimated ice, it may be possible that free OH ions are being released from some other process, other than water ice.

  • Clive Hartland says:

    It is obvious that a landing site for Philae is going to be a very difficult choice,
    Too exposed then a chance of disaster, in a dip then not very good pictures and shielded from transmission of images.
    There must be a lot of head shaking going on about this and decision making choices.
    A vantage point where images can be taken of events as they happen could be high up on the shoulder of the large end of the Comet.

    Clive

    • Donald Q says:

      I would pick a spot that is cliff-like, with no thick layers of dust to inhibit the harpoon and screws.

  • Donatas Garys says:

    Pardon my limited knowledge but isn't the surface of the comet incredibly soft? If the object isn't even massive enough to become round then I imagine surface being more like a sea of dust and ice in which you would sink. The probe landing must be feather-like to succeed, is that correct?

    • Dave Higgins says:

      Donatas,
      I believe its is supposed to be an icy snowball of loosely bonded dust and ice from the beginning of the solar system.
      Kinda doesn't look that way does it?
      I not sure the harpoons or the drill is intended to penetrate rock.
      If it was soft even with little gravity we might have expected a kind of a ball after 4 billion years due to shrinkage from sublimation and gravity pulling the loose aggregate together in some way in a slow merge (much like when lead flashing on old roofs begins to sag imperceptibly over time.
      So its going to be interesting as it unfolds as the current theory of how the comet forms looks a bit leaky

  • John Hill says:

    Its my understanding that a harpoon type mechanism will be used to anchor the lander to the surface. Looking at the many amazing pictures which have been taken to date, much of the surface seems to be either rock faces, dust or craters. I expect the choice of landing area will be difficult to agree upon without getting a lot closer. Can anyone explain the strange edges of the craters? They seem to be quite high, thin and jagged, possibly due to the low gravity and rotation of the nucleus affecting the way the dust and rocks settle in some sort of equilibrium? I agree that high up on the rock face would be an ideal landing area but I am not au fait with the harpoon and whether it can penetrate solid rock?

  • Welsh boyo says:

    Why is every 1 thinking that it all lightly packed together and hollow ? It been hit by many other rocks and still I 1 peace (how ever miss shaped). There was a comet around Christmas time and they said it was going to be spectacular but sadly it stopped having a tail well before it got near the sun and then died out when it was near the sun so there was just a small rock on it return journey. Perhaps there was ice but now it been around the sun then most of the starting materials have gone (unless they seen this coming from the much further out than I thort). But all in all this mission has been a real showing of skill of understanding our solar system just to get there. Keep up the good work ESA and thanks so much for sharing the info you find. Please keep us all up to date because we all just as intrested in this as you are 🙂

  • Laurence Smith says:

    Great hypotheses folks! I love that people are bringing up their own assumptions, as it gives a good number of focal points for comparison of what we think is there, and what is actually there.

    It certainly does seem that this comet might fly in the face of convention, what with the terracing, the sharp edges, etc.

    I wonder just how deep the dust might be that covers the 'main ground' of the comet? Hopefully the landing will not be in dust that is too deep to penetrate with their subsurface test devices. I suppose that is just one consideration of many concerning the landing location.

  • John Hill says:

    Maybe what appears to be dust from the current distance will turn out to be a mixture of dust, rock and ice as expected - measurements have already shown that the water vapour is being or has been expelled so I don't think there is any doubt that water is present and it must be pretty close to the surface at this distance from the sun. I expect Rosetta will have to get very close to determine the exact composition and granularity of the 'soft' surface unless this can be determined by other means? . It would be interesting to know what the expected temperature would be if the soft surface was composed entirely of dust versus a mixture of dust and reflective ice particles? The average temperature was measured at around -70 degrees, are we now close enough to compare the temperature of for example, the rock faces, soft material and inside craters?

    • Dave Higgins says:

      Hi John,
      if you look back at some of the other encounters of comets, Halleys, Borreli, Wild etc, you will see that there was little or no detection of ice at the surface, even at the locations of the out gassing?
      In all cases water was declared present in the comet tails.The comets though, were hot and dry. We already know that this comet is hotter than expected from existing theory, also there has been no announcement of ice on the surface yet, I would guess it could be detected if it was there?
      At one point the scientists from the US geological survey said of one of the missions ''We know the ice is there, its just well hidden''
      Is it there though? or is the water in the tail generated from some other chemistry?
      Is it time to believe our eyes and the data taken from the surface of the comet?
      I wish I knew the answer.

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