# Thread: Rosetta is There!

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Originally Posted by lpetrich
Where does that density value come from, Squink?
Wikipedia has it now
Latest? estimate here.
ESA from 2005:
A nucleus bulk density in the range 100-370 kg/m^3 is found for the nominal Delta P, while an upper limit of 500 kg/m^3
Obviously, the number will be refined now that we have something of known mass orbiting the comet.

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Thanks for the input Ipetrich .
Data will come in about its shape and its associated field as Rosetta will continue orbiting .
In the meantime I was wondering how to model the gravity around the comet by simple means .
Here's the simple model I used : two sphere's just near each other . I used a general density of 350 kg/m³ as an estimate .
Doing some basic calculation in excel the chart gives an idea about the gravitational force long the long axis .
It seems the "neck" is a region of low gravity .
The gravitation here might be around 0.0001 N/kg mass .
This would mean the Philae lander having 100 kg would have a force of only 1 gramForce on the surface !

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Originally Posted by Cougar
Any chance this will split the comet in two?
Not at all. Remember, the Philae's engine probably has less thrust than my late mother's economy sized cans of Aqua Net hair spray.

Then too, those would be considered HLLVs what with that comet's low gravity...

4. It still boggles my mind just how low this gravity is. I understand the lander has a camera, but I hope they can get some good landscape shots. If the orbital view is any indication, surreal is probably going to be an apt description.
I know many don't like it, but 2061: Odyssey Three is probably my favorite sequel to 2001: A Space Odyssey, and one of the events is a landing on Haley's comet. It'll be interesting to see how prescient the account shall be. No big jetting geysers so far, but perhaps it's too cold for that yet.

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6. They see that face, and they don't see the peashooter? Sheesh.

7. Warning, link is to the Daily Mail website.

8. Phil Plait's gonna love that one.

9. Can it's name be changed to Comet Rushmore?

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Ego, the living comet.

11. Smiley face crater right on top of its head.

http://blogs.esa.int/rosetta/files/2...M_20140807.jpg

12. Originally Posted by Superluminal
Smiley face crater right on top of its head.

http://blogs.esa.int/rosetta/files/2...M_20140807.jpg
Kinda cute.

13. Originally Posted by selvaarchi
More information on Rosetta.

http://m.space.com/26754-rosetta-com...40807_29286356

" Europe's Rosetta probe made its historic arrival at Comet 67P/Churyumov–Gerasimenko yesterday (Aug. 6), making Rosetta the first human-built craft ever to rendezvous with a comet with the intention to enter orbit.
Now flying about 62 miles (100 kilometers) from the comet, the Rosetta spacecraft is expected to gather data that will help scientists learn more about comets. Specifically, the findings will shed light on how the ancient, icy wanderers that roam through the solar system formed thousands of years ago.
The European Space Agency-operated spacecraft may also help scientists find answers to some of the most pressing questions in space science today."
Seems to me they're off by half a dozen magnitudes or more.
Last edited by Lord Jubjub; 2014-Aug-13 at 03:59 AM. Reason: grammar nazi myself with much embarrassment

14. Originally Posted by Lord Jubjub
Seems to me there off by half a dozen magnitudes or more.
Well, it's technically true. It was formed in a space of time that can be measured in thousands of years ago, just a whole bunch of them.

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Lovely 3D shot
The striped region is apparently part of the overhang between head and neck.

16. Here is a nice shot showing some internal structure? of the nucleus. In the months ahead there will be pictures from much closer, but even this is pretty amazing.
Notice the area on the cliff where you can see some parallel features. I will be interested to find out how they formed.

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Gecko Toe Forces may hold dust in place on Comet 67P/Churyumov-Gerasimenko

Forces that hold rapidly spinning near-Earth asteroid together discovered
The team studied near-Earth asteroid 1950 DA and discovered that the body, which rotates extremely quickly, is held together by cohesive forces called van der Waals, never detected before on an asteroid.
...
The researchers' findings also have implications for space exploration. For example, the European Space Agency's Rosetta spacecraft successfully reached orbit around Comet 67P/Churyumov-Gerasimenko last week and it may find a dusty surface dominated by such cohesive forces.
This is both surprising and delightful.

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Originally Posted by Superluminal
Smiley face crater right on top of its head.

http://blogs.esa.int/rosetta/files/2...M_20140807.jpg
It's tempting to think of this 'top-of-the-head' crater as an impact feature. Given its diameter, about half that of the head, and the very low density of the comet, one wonders that such an impact didn't destroy the head completely, though. The 'smile' is nearly a straight line. There is a similar straight, dark line across the forehead of the 'smiley face'. All very intriguing and odd.

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Nice review at Planetary Society:
Finding my way around comet Churyumov-Gerasimenko

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Complete with a spherical coordinate system for the comet's surface, though with very distorted lines of latitude and longitude.

That animation makes it rather evident that the comet is rotating about its short axis, its axis of largest moment of inertia.

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▶ 5 Fun Physics Phenomena - YouTube In the second of those 5, starting at 1 minute into the clip, the Veritasium gentleman attempts to flip a cellphone end over end. He finds that it ends up rotating around some other axis also. Spinning around its long axis or its short axis is, however, stable. It is rotation around its intermediate axis that is unstable. One can work that out with Newtonian mechanics applied to rigid-body rotation, and one indeed finds that result.

The general solution is rather complicated, but it can be worked out in closed form, if one considers Jacobi elliptic functions and elliptic integrals closed form. But one indeed finds that stability result from it.

22. Originally Posted by Squink
Lovely 3D shot
The striped region is apparently part of the overhang between head and neck.
Now that's just showing off.

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Looking repeatedly over the image animations of the comet nucleus, I wanted a concise description, in familiar terms, of its overall shape. Things seem to have progressed somewhat since the 'rubber duckie' stage.
I liken the object's shape to a sculptural bust-- like a three dimensional representation of a human head, neck, shoulders, upper chest, and upper back, which rests on a squarish, tabular base.
The 'head', rather short and broad suggests the 'potato' shape or triaxial ellipsoid, noted in asteroids and comet nuclei before. The 'body', or at least upper torso, combined with the tabular base, appears blocky, with flattish sides at approximately right angles to one another. This seems atypical of similar bodies, seen in space before.
The projection of the 'chest' forms a transition region between the neck and the base. At the back we see a flattish, but slowly curving surface, comparable to the upper back, neck, and back of the head of a human subject, with the head bent forward, as if looking downward.

24. Originally Posted by ravens_cry
It still boggles my mind just how low this gravity is. I understand the lander has a camera, but I hope they can get some good landscape shots. If the orbital view is any indication, surreal is probably going to be an apt description.
I know many don't like it, but 2061: Odyssey Three is probably my favorite sequel to 2001: A Space Odyssey, and one of the events is a landing on Haley's comet. It'll be interesting to see how prescient the account shall be. No big jetting geysers so far, but perhaps it's too cold for that yet.
So, they have already detected outgassing (jetting) from the comet, and we are still 3 AU from the sun. In then next few months, as the sun-come distance decreases, we should see more activity. Don't give up yet!

25. Originally Posted by antoniseb
Here is a nice shot showing some internal structure? of the nucleus. In the months ahead there will be pictures from much closer, but even this is pretty amazing.
Notice the area on the cliff where you can see some parallel features. I will be interested to find out how they formed.
I can attest to the fact that there is a lot of debate at SwRI, where several Rosetta researchers are. Our Friday morning science discussions have been lively!

I'll keep my ears open because they get newer and higher resolution photos every day.

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Now how cool would it be if you saw the two chunks split?

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Originally Posted by antoniseb
Here is a nice shot showing some internal structure? of the nucleus. In the months ahead there will be pictures from much closer, but even this is pretty amazing.
Notice the area on the cliff where you can see some parallel features. I will be interested to find out how they formed.
There appear to be both vertical and horizontal linear features crossing each other. Emily Lakdawalla noted this, and compared its appearance to fabric. It almost looks as if granular material on the surface slid down from part of the 'head' onto the 'neck', exposing the linear features underneath.

28. I have a CT friend who sent a video outlining purported "unaltered images," showing some features not seen in the public domain. I don't want to give any credence to the imagery. I suspect the images in that video are indeed altered to show something that is not really there., so I'm trying to figure how much opportunity there was to do this altering. I've seen several posts on here from folks who said they were watching in "real time." My question is, for folks watching from a public computer, is there any significant lag time between downlink to earth, and accessibility in the public domain? Say...15 minutes between the time ESA receives the signal and John Q. Public being able to see what is disseminated? I'd like to debunk this by saying to my friend that there would not be enough time for some nebulous authority to perform some scrubbing. Does anyone on here know how quickly we see the raw images?

29. Originally Posted by Polyrealastic Observer
I have a CT friend who sent a video outlining purported "unaltered images," showing some features not seen in the public domain. I don't want to give any credence to the imagery. I suspect the images in that video are indeed altered to show something that is not really there., so I'm trying to figure how much opportunity there was to do this altering. I've seen several posts on here from folks who said they were watching in "real time." My question is, for folks watching from a public computer, is there any significant lag time between downlink to earth, and accessibility in the public domain? Say...15 minutes between the time ESA receives the signal and John Q. Public being able to see what is disseminated? I'd like to debunk this by saying to my friend that there would not be enough time for some nebulous authority to perform some scrubbing. Does anyone on here know how quickly we see the raw images?
You ask good questions. The Rosetta team hasn't released any new images in over a week. I asked this morning, so my information is current. Anyone claiming to be have images not in the public domain or observing in "real time" is either on the Rosetta Team or they are deceiving someone.

Only images that are released to the public are available. My office neighbor is on the Rosetta team, and he doesn't even show us the newest images. :/

30. Here's an image taken on the 20th, showing parts of the comet not shown before.
http://www.esa.int/spaceinimages/Ima..._2014_-_NavCam

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