Rosetta - Early Orbital Operations at Comet 67P C-G, August 6, 2014 - November 13, 2014 Options

[Explorer1]

http://www.esa.int/spaceinimages/Images/20...de_of_the_comet

Our first glimpse of the night side! I thought it would involve a lot more waiting until after perihelion.

[mcgyver]

Talking of colors, this is one of a few images where the comet really looks like carbon:

http://www.esa.int/spaceinimages/Images/20..._October_2014_a


Talking of filters change time:
in 1 second the comet should rotate 2*pi/45720 = 0.0014 rad (12.7 hours period); assuming 2 km radius this would mean 0.0014*2000 = 2.8 meters surface shifting in 1 second; assuming 0.5m/pixel resolution this would mean 6 pixel "smear" for each color channel.
This should result in acceptable color images (if my math is correct)

[mcgyver]

Our first glimpse of the night side!

Is there any picture showing the rotation axis of the comet? I can't find anyone.

ADMIN: From this same thread. Don't forget to use the Forum's search tool or read back through the topic.

[fredk]

Our first glimpse of the night side!

Very nice shot. But I don't buy the description in the caption:

Light backscattered from dust particles in the comet’s coma reveals a hint of surface structures.

The coma is far fainter than the directly illuminated surface, and I can't see the coma detectably illuminating the dark side. If you look at the full frame, I think it's pretty clear what's going on. The visible portion of the dark side, circled in my pic, is being illuminated (arrow) by sunlight scattered from the far bits of directly-illuminated surface that I've drawn an ellipse around:

[foxfire]

http://www.esa.int/spaceinimages/Images/20..._October_2014_a

To my eye--at least for portions of the photograph--there seems to be a system of strata generally running in the 11:00-5:00 direction composed of alternating dark and light bands. These are well seen on the dimly lit "inner wall" of the central "cave" as well as at the very margin of the comet surface where it is bounded by the blackness of space on the upper right of the photograph (especially in the expanded view). The different bands appear to have a differential resistance to whatever "erosive" process can occur, if the "up-and-down 'laddering'" seen on the well-lit left "exterior surface of the cave" is representative.
Should these alternating bands reflect different mechanisms of deposition/consolidation during periods of perihelion "emissivity" from those operating during the subsequent periods quiescence of C-G, then they may be used to estimate the age of the periodic comet--somewhat like tree rings or varves.
I personally don't know enough to be calculate the thickness of the layers given the data accompanying the photograph, but I am sure this can be done. Once known, one can start to give some ballpark measure of the volume of material required to form the layers; which may support or undermine the "theory of periodicity."

[Gladstoner]

To my eye--at least for portions of the photograph--there seems to be a system of strata generally running in the 11:00-5:00 direction composed of alternating dark and light bands.

My guess is the striations are a joint pattern (if that is what it would be called in this case) that resulted from 'tectonic' stresses and large impacts.

Speaking of tectonics, I wonder if the barbell shape of the comet could have formed due to a progressive deterioration of the neck region caused by the combined effects of rotational centrifugal force and cometary erosion (de-icing of matrix and outgassing erosion). If so, such nuclei that start out merely elongated (egg-shaped) may tend to end up with barbell shapes before they split outright. That may explain similar shapes with other comet nuclei as well as with commonly observed cometary splits.

[dvandorn]

Boy, it's good to see some new OSIRIS images being released. Extremely impressive! (I just filled a swear jar to overflowing with this most recent release.)

It's going to be a very exciting time when the OSIRIS images hit the international version of the PDS and we can see more than a handful of them... maybe even more exciting than the preceding six months.

-the other Doug (With my shield, not yet upon it)

[atomoid]

...I wonder if the barbell shape of the comet could have formed due to a progressive deterioration of the neck region caused by the combined effects of rotational centrifugal force and cometary erosion (de-icing of matrix and outgassing erosion). If so, such nuclei that start out merely elongated (egg-shaped) may tend to end up with barbell shapes before they split outright. That may explain similar shapes with other comet nuclei as well as with commonly observed cometary splits.

i like that model, but am also adding here armchair speculation in suspecting the configuration forms when two mutually rotating clumps lose centrifugal energy to the tidal stress/rearrangement of rubble, eventually settling together and building the junction into a sort of barbell isthmus by infalling and settling flotsam/jetsam over the eons as the two lobes contract and their surface remnants recede from the junction, so it should devolve towards a barbell cylindric rather than thinning the barbell isthmus towards eventual collapse. The pole being perpendicular to the long axis seems to support such a scenario, ..not sure if that is also the case for other barbell comets though.

[Gladstoner]

i like that model, but am also adding here armchair speculation in suspecting the configuration forms when two mutually rotating clumps lose centrifugal energy to the tidal stress/rearrangement of rubble, eventually settling together and building the junction into a sort of barbell isthmus by infalling and settling flotsam/jetsam over the eons as the two lobes contract and their surface remnants recede from the junction, ....

I can see that happening as well. Perhaps such comets could follow two possible paths:

1. Erosion proceeds more quickly than deposition/settling, which leads to thinning of the neck until the comet splits. 67P may be moving in this direction.

2. Deposition/settling proceeds more quickly than erosion, which leads to slowing and possibly termination of sublimation and erosion of the neck area. Comet 103P/Hartley may be an example of this.

Since cometary processes can be a messy affair, it would be hard to predict an ultimate outcome. Of course there are additional wild cards -- e.g. variation of distribution of materials within the nucleus, gas pocket outbursts -- that could 'shake things up' dramatically. Also, the 'barbelling' process may be more likely with smaller comets than with larger ones.

[Phil Stooke]

Since we haven't yet seen the southern side of the comet, we don't really know that it is a 'barbell'. If later images show that the neck extends to the south, it's a sort of barbell, but if not, the 'neck' is just a depression on one side of the nucleus. So speculation might be a bit premature.

Phil

[fredk]

If it is a barbell, and if it formed by the joining of two bodies, I might expect the two to be more loosely connected than if it formed by the erosion of one body. In that case, around the time of greatest activity near perihelion I might expect differing jet reaction forces across the nucleus to lead to shifts in one body perpendicular to the line joining the two. That should lead to cracks (like we appear to have seen already) opening or closing near the neck. Depending on the details of the gravitational field and connection of the two joined pieces, we might even see vibrational modes - periodic opening and closing of cracks.

I can't wait for perihelion...

[neo56]

I have updated my Rosetta gallery, here are the 4 most recent NavCam mosaics:

[Sacha Martinetti...]

2di7 and Titanio44 had published an awesome color of the comet, chosen as APOD the September 15th.

Two more :


Comet Churuymov Gerasimenko 18 October 2014 vc par 2di7 & titanio44, sur Flickr


67P RosettA navcam 26 October 2014 vc par 2di7 & titanio44, sur Flickr

The originals are bigger.

I will link the picture of the site J on Philae's topic.

[Sacha Martinetti...]

Just one more, though I can't remember if Emily didn't linked it from her blog. But if not :


Comet 26 09 14 NavCam Mosaic vc par 2di7 & titanio44, sur Flickr

[bobik]

I have updated my Rosetta gallery, here are the 4 most recent NavCam mosaics:

Your caption of the NAVCAM image from 4 November 2014 is wrong. The LARGER lobe of the comet is seen in the foreground.