I wonder if there will be any way to determine just how long C-G has been in the inner Solar System. Its perihelion prior to a 1959 encounter with Jupiter was 2.7 AU, but I don't know if its prior orbital history can be extrapolated much earlier than that.

I doubt if its precise orbital history can be traced much further back, but dynamical modelling might be able to provide statistical information such as the long term average time interval between Jupiter encounters and the likely distribution of perihelion values.

On the specific question of whether any of its previous orbits have brought it closer to the Sun than its current one, there may be clues in how much its activity at perihelion changed pre and post 1959. I imagine somebody has studied this.

I'm trying to figure out how that could be studied or even modeled given how little in situ data we really have about comets. Their behavior is notoriously unpredictable, and that has to be related to both composition and structure. Might prove difficult to draw enough parallels between individual comets to derive a consistent set of methods to estimate things like long-term orbital histories.

But, of course those kinds of questions are why Rosetta was launched in the first place.

Where did this amazing image come from? I don’t see it here or from Rosetta.

From the recent 4 image NAVCAM mosaic, possible boulder trials (far lower right)...?

Looks like an artistically enhanced version of this:
(Linked here by Phil in post 251)
Click to view attachment
http://www.esa.int/spaceinimages/Images/20..._September_2014

Where did you find it? I'd like to know who made this rendering. This is the first image of the comet I've seen that lets you believe you are looking at a black surface. The subtle colouring is entirely plausible too. Good job. Informed artistic versions of space images have an important role in making distant worlds real to us.

I found this picture at APOD [url="http://apod.nasa.gov/apod/ap140915.html"]
following the other links on this page, I got [url="https://www.flickr.com/photos/lunexit/15265360485/"]

Is this artists impression or based on real data ?

Damn. I saw it somewhere in Twitter. I grabbed it thinking it was just some official release from the Rosetta team. When I didn’t see it there later I forgot to go back to where I found it and now I cannot find it through my history links.

It doesn’t look artistic. That color looks like it is really in there not just superimposed in Photoshop on multiply or anything.

Ah ha!

http://apod.nasa.gov/apod/ap140915.html

I see now that someone just posted that before me… but look at this one by the same person who made the one I posted.

https://www.flickr.com/photos/lunexit/15031557890/

Oh my! The beauty of this heavenly object is breath taking!


Strangely Iapetus Comes to mind when I look at this image ^^

When I look at that image a certain Odyssey comes to mind...
Click to view attachment
Epic stuff for sure...

So, does anyone know who this is: Copyright All rights reserved by 2di7 & titanio44?

From their flickr page (https://www.flickr.com/photos/lunexit/) they are doing a lot of image processing.

Whoever they are, they need a UMSF account, pronto! Desktops galore...

I like to see when they get in conflict with the people who have THE copyright for the image. I know of a few cases where the Halley images of the HMC were used and this ended not nice for the people who did this without being permitted.

The people who built the camera do not give away their copyright this is a big difference to the NASA missions.

Their names appear under the APOD for September 15th (as linked by mgrodzki in post 360 above) along with all the proper credits to ESA etc. Perhaps attitudes have softened since Giotto, accepting the inevitable at the very least.

What a gorgeous image! But isn't the overall albedo very low? So what looks like snow-covered rocks must be more like black-dust covered rocks. I'd love to know what the albedos of the regions are.

I thought the same thing. I haven’t seen any thing that looks like that as of yet. On top of that… see the part in shadow, what would be the chin if that were it’s head. That looks to me like sprayed materials doesn’t it? Like the jets that form the tail strike that area on their way out and create a caking of materials there. Similarly to how it looks when you spray mount too long in one spot (yes, I am a designer who went to school pre-internet when they used such things). Even if the albedo is way off… it still looks like that kind of process.

"Elizabeth and Mark" (English Translation) have some nifty images here including:

Neck Jets - various enhancements

Close up of neck crack

http://www.aliveuniverseimages.com/special...ta-per-rompersi

Accompanying the images there is speculation that some white spots in images (both fine and coarse grains - larger white spots) are visible. Makes me wonder if the boulders we see scattered on the surface are large jet fragments that have resettled back onto the surface from prior orbits.

Just for giggles… and suitable for framing on your walls!

I may have “dust and scratched” a few boulders out by accident along the edge of the sunlit part we are referring to as the head. But any specks in the dark area would be noise since there is little to no light in that area.

Now I am confused… I cannot decide if that is shadow under the head or if that is bright material emerging from dark where you would expect sunlit surface. It does looks amazingly similar to the way Iapetus goes from dark to light in small areas.

Yes maybe some Iapetus like features there in the head. I suppose I haven't been looking at the raw images enough to really know, though one might check whether the dark specks in front of the brightest jet regions are also noise (in post 370)? Overall would we expect to see any individual particles flying around during the mssion?

There is considerable noise in the space around the comet. So I am assuming most of the noise throughout is actually noise. Some also seem to have a direction or in other words, seem to be tall and vertically stacked 2-4 pixels which I am not sure what would cause that (not star trails) but I think these are less likely to be boulders.

I think there's a velocity problem here. For an ejected 'boulder' to resettle on the surface it would have to be very gently propelled, given the low escape velocity - more of a putt than a drive. The jets look pretty straight to me, not swirled into spirals by the comet's rotation. That suggests that material in the jets has easily exceeded escape velocity by the time it leaves.

If indeed there are loose boulders adhering to the surface by gravity alone, I think they must derive from gentler processes such as slumping, settling and slow motion landslips in response to internal mass wasting.

True, but I expect a block would be very loosely coupled to the jet - not accelerated very much however fast the jet was blowing past it. And it might be more shoved aside than lifted up high and then falling back.

Phil

You'd have to be very very careful with those blocks. How many would you lose before you managed to recapture one? If you were too careful and the blocks were merely levered aside then they ought to be located around the vents. We don't see them concentrated in that way.

In fact, one of the problems given the presumed active age of this comet is the relative lack of boulder-sized debris. And isn't it peculiar that most of the larger blocks appear to be relatively newly placed, not shrouded in the grime of ages? Many of the upward-facing sublimation pans appear to be self-choked by their own infall, while the most recent activity seems to be from edges and overhangs that have dumps of smaller-sized debris associated with them. But even that debris is not pervasive across the surface as you would expect on such a long-eroded object (eg, lunar regolith). Either boulders do get ejected regularly, or they were weakly adhered or icy in the first place. In fact, would one expect large, rocky boulders even to be part of the makeup of an object that formed so distantly from the Sun? As usual, I'm sure the scientists using OSIRIS closeups have worked out some "rock" size surveys already and have some insights into The Comet Recipe.

My previous post ignored the most evident count of comet particle size distributions: observable meteor showers that are associated with comets. Obviously the distribution favors sand-to-pea sized rocky particles, and the occasional recovered meteorites from those showers were clearly former boulders. Therefore I do expect this comet to have real rocks of all sizes. I'm still puzzled though that there are not vast piles of material that was exposed in place--perhaps it is trapped under the carbon layer and gets loosed only when something breaks. As for the largest blocks, their unshrouded appearance indicates either very little infall of low-velocity debris, or very fresh placement. Or something else... I'd better leave the door of interpretation open.

An interesting fact from my research just now: gas-rich carbonaceous chondrites are more likely from asteroids than from comets (Do Stony Meteorites Come From Comets? http://www.sciencedirect.com/science/artic...19103575901323). Not that comet debris never falls , but it would seem more rare than that of asteroid origin.

Couldn’t the boulders have simply been propelled from a vent and just managed to land across from that in this dark region?

By the way, anyone know for sure if this dark region is actually dark material or in shadow, or perhaps not real but enhanced by the people that did the original processing? I am not on any level a scientist, but the areas that are dark because they are in shadow go black whereas this is more dark grey so it looks to me like dark material. I am guessing they enhanced this area but didn’t enhance the dark area at the top of the image. The angles of the light, etc surely suggest that this area should be in shadow.

My alternate boulder theory, just to populate the space of ideas. They are lumps of slower ablating material that gets left behind as the material around them is removed, until the stem holding them up collapses and they "redock" with the mother ship. So they fall close to their point of origin.

A good point. It is worth reviewing the several types of image processing used in the pictures we've seen so far.

Flat, muddy-looking images are closer to what you would actually see if you were there--those original tones have not been appreciably brightened to enhance the difference between "dark" and "really dark", therefore these image are better for judging the true brightness of objects on the surface.

Sometimes the intent is to show more detail in the shadows (as with jets and regions receiving indirect or diffuse sunlight), in which case the brighter regions may be completely washed out in favor of better showing barely registered detail in a very small range of the original image data.

The pictorially striking images we've seen in recent posts have had the dynamic range (contrast and gamma) stretched so that original "dark" appears much lighter. This creates the illusion of Earth-like snowy mountains and boulders that look like snowballs. It is tempting to think of these lighter versions as showing ice or snows, but as we've seen from Mars Pathfinder mission where the landing rockets and scoop actually exposed some water ice, such scrapes *quickly* lose brightness as the surface of the ice sublimates, leaving behind a layer of whatever particles were embedded in it.

As the comet becomes more active, we may start to see original images with a higher inherent dynamic range, no stretching needed. At that time, a fourth image processing technique may be come necessary: mapping extreme highlight regions downwardly into more detailed gray tones, similar to HDR processing in artistic photography.

If you're referring to the circled area:
Click to view attachment
That's in shadow from direct sun, but is able to receive reflected sunlight from the near lobe, so is faintly visible. We've seen this on other Rosetta images. It's analogous to Easthshine on the moon, with the far lobe the moon and the near lobe the Earth.

The near lobe shadowed region has nothing bright on Rosetta's side of it (apart from extremely faint stars), so appears completely dark.

Yes… of course. Like Saturnshine on Enceladus. Why didn't I think of that. Thanks for pointing out what should have been obvious to me. It is good to know that the white here is dark and the dark is very dark… but the phenomenon still seems similar to me as we have seen elsewhere. Just with materials less bright.

ADMIN: Edit.

but remember , for the next 6 to 12 months all we will see are 60 to 80 % compressed JPEG's
once the original images are in PDS then we will know

It is going to be an amazing dataset. I so much want to see what they have got. They must have these absolutley marvelous sequences of OSIRIS images. Judgeing by the quality of the shapemodels that they showed at the landingsite presentation.

I snipered some horrybly compressed OSIRIS frames from the presentation and made this anaglyph:

Click to view attachment

I realise this image release issue will be a recurring theme. However, I am told that at least one individual has already submitted a journal paper based on the compressed JPEG's. From what I hear, it was not accepted. But people are not happy. Considering the blood, sweat and tears that went into putting the OSIRIS consortium together and raising the funding, perhaps it's not so hard to understand the nervousness about being beaten to publication.

I can see that. I see a pretty significant difference between a mission like Rosetta and MER or MSL. There were probably good reasons before MER or MSL landed to expect that it was unlikely that any significant discoveries could be made on the basis of the uncalibrated jpegs alone. Therefore it wouldn't've been seen as a big risk to release those in real time.

But for a mission like Rosetta you might reasonably expect that the jpegs might provide real, publishable discoveries, since comparatively little is known about comets as opposed to Mars. Hence the reluctance to provide all the images, even as uncalibrated jpegs, in real time.

So as far as enthusiasts go, MER/MSL were ideal in that the images had relatively low scientific interest but great interest to the amateur crowd. With Rosetta, the stakes are just too high.

Strongly disagree. The early Opportunity images in particular were a scientific revelation. Concretions, Vugs, Cross bedding, fine laminae - it was a geomorphological treasure trove.

The team knew that was a risk. They trusted the scientific community to respect their PDS delay and not attempt to beat them to publication. It worked.

I'm very disappointed to learn that someone has failed to exercise that same professional restraint with Rosetta.

for my self the rate ( i should say " lack of..." ) images is a bit of an issue
it is rather hard to convert the few few images into a 3d mesh
( for more on that see the Other thread)

for a low res mesh even a bunch of 80% to 90% compressed jpg's ,with all those artifacts, is just fine when the out put would be a image that is 720x 361 px.

To continue off on this Martian tangent, I don't know how high the bar is in planetary geology publishing, but could someone really have published based on uncalibrated pictures of blueberries and vugs, without any minites/apxs/MB/calibrated pancam compositional information for context? I'm curious what the geo-folks here would say.

My guess would be that trust would not have been enough for the MER project to rely on. Scientists can be pretty ruthless at times.

Hello All,

Since this is my first post here, I want to firstly thank you all for providing such an excellent, well-informed and well-moderated discussion forum. The "signal to noise ratio" of posts on UMSF is off the charts compared to anywhere else I've been, so I'll try to hold my posts to the same high standards of excellency I routinely see here; which is to say I probably won't be posting very much.

After going a few days without any new images from Rosetta, I turned my attention back to the most recent image release (Sept 19) and decided to see if I could resolve the jets any further:

http://i.imgur.com/44CuMci.jpg

Please excuse the amateurishness of this - I'm just learning image processing, and since it was pre-stitched I wasn't able to correct it with the dark frame helpfully posted a few pages back. I simply mapped the darkest greys in the image to a 3-color gradient to bring as much detail as possible out of the jets.

I purposely did not try to limit this to the outline of the comet, as I wanted to see if there were any visible foreground jets against the shadows. It definitely appears to me as if there is some jet material between the neck and the shadow on the larger lobe, as someone mentioned before. There also appears to be some activity seen off the edge of the larger lobe besides the obvious jets on the neck. One thing I'm curious about - the entire silhouette of the comet seems to have a bit of "fuzz" to it. Is this low level sublimation happening pretty much everywhere? Or maybe light scattering from a thin "atmosphere" of dust? Or just an artifact?

Additionally, I wanted to say that Phil Stooke's comment a few weeks ago regarding the mystery of why comet jets are collimated like this piqued my interest and revealed some good reading, if anyone else is interested:

http://www.chem.ucla.edu/~itkin/publicatio...ticle_crifo.pdf
(The J. Crifo paper I think Phil was referring to, suggesting collimation as a result of dust being squeezed between two or more interacting gas cones)

http://www.lpl.arizona.edu/~yelle/eprints/Yelle04a.pdf
(Formation of jets in 19/P Borrelly by subsurface geysers)

http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2548.pdf
(Perhaps confinement isn't necessary for collimation)

Finally, I have a sort of unrelated question which I'm hoping an expert out there may be able to answer: As I understand it, this paper[1] published earlier this year confirmed the longstanding hypothesis that solar wind bombardment of interplanetary silicate dust can form -OH and H2O due to H+ ions in the solar wind interacting with oxygen in the dust minerals. Is it possible/plausible that a significant amount of H2O content on comets could be a product of this "SW radiolysis" process? If so, would Rosetta have any way of determining this?

[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3918814/ (Detection of solar wind-produced water in irradiated rims on silicate minerals - Bradley et al)

Same as Cassini. But let's remember who provided the funds that were raised.

100% agree with you Doug : the "proprietary period" scheme given to the OSIRIS scientists is a real shame for ESA
The controverse is mounting high in France and Germany with pro-space organizations complaining officially now.
And, after all, we are also "proprietaries" of those images, because we paid for them through our taxes...

Also disappointed to learn that someone has failed to exercise that same professional restraint with Rosetta.

One of the reasons I vetted mentioning the vents pointed out by imaging leader Holger Sierks during the Landing Site press briefing was that those images were not in the published package on the blog site.

Did not want to rock the boat.

Sad situation. I understand both sides although I strongly lean to the give us everything now.

The power of crowd sourcing unleashed.

Edit: an alternative on their part to (understandably) hoarding their hard-earned data is to release it and ask the crowd to work on their behalf. At the highest resolution there might be thousands of interesting features to put eyes on, and crowd sourcing has proven to be an excellent method of data exploration.

I noticed that too. My guess was scattering of light inside the optics.

Playing with draping navcam images over my shapemodel.

Made a short flyby animation:

http://mattias.malmer.nu/2014/09/passing-into-the-light/

Wow, stunning! Thanks.

Phil