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Rosetta - Post Separation Ops at Comet 67P C-G, November 14, 2014 -
DFinfrock
post Nov 27 2014, 12:48 AM
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QUOTE (SteveM @ Nov 26 2014, 09:35 PM) *
... the jets are primarily pointing toward the Sun, while a comet's dust and ion tails point away from the Sun. Can Rosetta observe the process by which the trajectory changes as they become tails, or is Rosetta too close to see that effect?


Absent any atmosphere, there is no air friction to slow down the jets at they stream outward from the surface. My guess is that as the comet's surface heats up (on the sun-ward side) the jets would be streaming directly away from the surface, or towards the sun. It would only be when the comet falls deeper into the sun's gravitational well, and picks up speed, that the tail is "left behind".

I await someone more knowledgeable about comets to correct me.
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Phil Stooke
post Nov 27 2014, 01:16 AM
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OK...

http://hubblesite.org/reference_desk/faq/a...cat=solarsystem

Phil


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fredk
post Nov 27 2014, 01:16 AM
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My understanding was that it was the pressure of the solar wind that forms the tail(s). So heating on the sun facing side leads to jets towards the sun, which eventually are deflected by the solar wind to form the tail.

If there were no solar wind, particles in a jet pointing towards the sun would presumably get ahead of the comet rather than be left behind (at least prior to perihelion).

Edit: Phil beat me by less than a minute!
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SteveM
post Nov 27 2014, 03:52 AM
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Thanks for the comments and for Phil's good link. The question remains, however, of what details Rosetta will be able to provide about the process changing jets emerging on the sunward side of the nucleus into tails streaming away from the Sun.

Steve M
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Gerald
post Nov 27 2014, 11:28 AM
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Small grains should be more susceptible to solar wind and radiation.
The GIADA instrument should be well-suited to investigate this question in very detail:
QUOTE
GIADA (Grain Impact Analyser and Dust Accumulator) will measure the number, mass, momentum and velocity distribution of dust grains in the near-comet environment. Giada will analyse both grains that travel directly from the nucleus to the spacecraft and those that arrive from other directions having had their ejection momentum altered by solar radiation pressure.
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SteveM
post Nov 27 2014, 01:55 PM
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GIADA should provide interesting velocity data. Look forward to more GIADA insights into dust particle trajectories since since this early detection of a few dust particles.
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neo56
post Nov 29 2014, 08:58 AM
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NavCam mosaic of 26 November. The rotation of the comet has been substantial in the twenty minutes that passed between the two lower images, resulting in artifacts in the stitching process.


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eliBonora
post Dec 5 2014, 09:11 PM
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1 December NAVCAM from 30.1 km



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ngunn
post Dec 5 2014, 09:28 PM
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Beautiful. Thanks for sharing that. It's amazing to pan around that view. What a place!
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Dan Delany
post Dec 7 2014, 01:13 AM
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Lovely mosaic eliBonora! The one on the ESA blog has a blurry seam, where the foreground and background limbs meet, that had me scratching my head until I saw yours smile.gif

Here are a couple attempts at anaglyphs from the Dec 1st and 2nd NAVCAM images, made from the slices where the bottom two (foreground) images overlap. Some artistic liberties have been taken to account for areas which were shaded in one image and lit in the other.
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eliBonora
post Dec 8 2014, 04:44 PM
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QUOTE (Dan Delany @ Dec 7 2014, 02:13 AM) *
Lovely mosaic eliBonora! The one on the ESA blog has a blurry seam, where the foreground and background limbs meet, that had me scratching my head until I saw yours smile.gif


Thank you Dan. Nice anaglyphs.
I think the difference is that we combine these comets by hand and we don't use the software's blending option.


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neo56
post Dec 10 2014, 09:42 PM
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My take on NavCam mosaics from 30 November to 7 December:


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Phil Stooke
post Dec 11 2014, 05:33 PM
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The latest Navcam blog shows new - or apparently new - features in the neck. Here's a comparison between October and December images (December on the right). I would suggest a close examination of images would probably show more things like this.

Phil

Attached Image


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Phil Stooke
post Dec 11 2014, 07:51 PM
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Sure enough, here's a comparison between 24 September and 9 December with the new feature on 9 December noted. Differences in lighting and resolution are small enough that I think this is a real change.

Phil

(PS... must work on book... must work on book... aaaargh!)

Attached Image


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walfy
post Dec 11 2014, 09:44 PM
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QUOTE (Phil Stooke @ Dec 11 2014, 11:51 AM) *
...I think this is a real change.
Phil


Wow, those changes are amazing! Looking forward to the discussions about this.
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