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{at}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{at}NASA
 
 
Regards,
 
Roger

--- D'Bridge 3.99