Rosetta Comet May Be a Contact Binary   
       
   This news release is reprinted courtesy of the European Space Agency, which is   
   leading the Rosetta mission to Comet 67P.   
       
   July 17, 2014: The European Space Agency's Rosetta probe is approaching Comet   
   67P/Churyumov-Gerasimenko for a historic mission to orbit and land on the   
   comet's nucleus. As Rosetta approaches the comet (now less than 9,000 km   
   away), the form of the nucleus is coming into focus, and it is extraordinary.     
   http://tinyurl.com/mby8lkn   
       
   Comet 67P/C-G on 14 July 2014. Credits: ESA/Rosetta/MPS for OSIRIS Team   
   MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA   
       
   This week's images of comet 67P/Churyumov-Gerasimenko reveal an irregular   
   shape. There were 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.   
       
   http://tinyurl.com/n24xo2j   
       
   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   
       
   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.   
       
   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.   
       
   http://tinyurl.com/o8hzkqp   
       
   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   
       
   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.   
       
   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. With fewer than 10,000 km to go before   
   the 6 August rendezvous, our open questions will soon be answered."   
       
   Credits:   
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   Web Links   
   European Space Agency home page   
       
   Rosetta -- from the ESA   
       
   Rosetta -- from NASA   
       
   NASA Instruments on Rosetta   
       
   Rosetta Comet Comes Alive -- from Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)