APOD: Explore Rosetta's Comet (2016 Oct 03)

[APOD Robot]

[img]http://apod.nasa.gov/apod/calendar/S_161003.jpg[/img] Explore Rosetta's Comet

Explanation: What would it be like to fly around a comet nucleus? To find out, just wait for your WebGL-compatible browser to load a detailed digital model of Comet 67P and then -- go exploring! With a standard mouse, the left button allows you to rotate the comet, the right button allows you to move the comet around, and the scroll wheel allows you to zoom in. ESA's robotic Rosetta spacecraft orbited Comet C67/P Churyumov-Gerasimenko from mid-2014 until last Friday, when, after a remarkable and successful mission, it was intentionally set down on the surface and powered down. Among many notable scientific achievements, Rosetta allowed humanity to better understand where comet jets form on comets as they near the Sun.

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Why for parts of comet (low detail, not covered by named regions) there is no data? Is it result of probe forced to orbit in a weird way so that these regions are unexplored? Visualisation bug? Visualisation isnot using full data?

[Kaarlo]

Comet nucleus 67P, clearly enough, is not a binary object but a monolith with parallel primary layering in the upper and lower lobes, and the ”neck”. The prevailing rock type, as detected from close-ups, is flow breccia. Feeder dyke swarms almost perpendicuarly crosscut the layering and consistently run through the lobes plus neck. The neck may be formed, at least partly, of extensive columnar basalt layers.
Stratigraphically, the lowemost unit appears to be the large lobe, followed by the less erosion-resistant neck, topped by the small lobe. Gross flow direction runs form upper right to lower lef (ref. video start position).
The low mean density (0.533, Wiki) of 67P likely results form high vesicularity indicating deposition in shallow water environment or on dry land. Primary volcanic layering and dyke contact surfaces control much of the present form of 67P.
Comet nucleus 67P – just as asteroid Itokawa (Geologi 2/2011, pp. 44-48) – appears to be a chunk of planet-scale oceanic crust, likely torn off Proto-Earth in the collision with Proto-Moon some 4.5 billion years ago. Countless gas and/or water-filled vesicles contained in basaltic MOR-lavas dry up in the vacuum of space – the fumes jetted out along fractures collect around the comet nucleus as coma and represent geochemistry prevailing in and on the Proto-Earth.

[Case]

Why for parts of comet (low detail, not covered by named regions) there is no data? Is it result of probe forced to orbit in a weird way so that these regions are unexplored? Visualisation bug? Visualisation isnot using full data?

I wasn't expecting uncharted territories either, after two years of exploring, but it seems 100% coverage wasn't on the agenda. It is weird seeing the ‘smooth’ side of the comet in this rendering.

[JohnD]

Kaarlo,
I got excited at first, reading your post, because you speak geology and might be able to answer my questions (see previous, Farewell Rosetta thread http://asterisk.apod.com/viewtopic.php?t=36425 ).

Then I read on. Kaarlo, one of the most interesting discoveries from Rosetta was that the water gassing out of the Comet was high in deuterium. This conflicts with the standard theory of how Earth got its water, because water here has three times less. This also means that 67P can never have been part of Earth.

Please consider this, and revise your opinion. I'd be most grateful for your geological ideas on how apparent strata can form in a celestial object, in the absence of liquid water and in microgravity. Also, as above, graded scree slopes, and apparent alluvial deposits.

JOhn

PS Meant to say! This is a stunning display! I can't think of any previous APOD or other astronomical image shown online, that shows you as much about an object. Well done to the APOD team for securing it and enabling its download.

[Kaarlo]

John, thanks for your comment and the link therein. Now, please consider this, and perhaps revise YOUR opinion.
Water - high in deuterium - degassing from 67P does NOT refer to water in today's Earth but to the pre-collision primordial water in Proto-Earth.
Nobody knows (that I know;-) what was the hydrogen isotope composition in Proto-Earth AND the colliding Proto-Moon - and what kinds of element exchange took place during the collision. In any case, much - but likeley not all - of Proto-Earth's hydrosphere was ejected to space - and (some of) that water may now exist in Jupiter's icy moons.
Also please note: at that (Pre-Collision) time Jupiter's orbit was different from today's. First, Jupiter likely dragged the Proto-Moon to collision course and later dragged the resultsing fragments to their present orbits. I hope an astronomer would elaborate on this aspect.
As a geologist, I simply cannot omit - and keep silent on - what I see in 67P: a partial cross section of Mid Ocean Ridge complex.
Also please see this:
http://www.geologinenseura.fi/geologi-l ... makela.pdf
..and this:
http://www.geologinenseura.fi/geologi-l ... Makela.pdf
Thank you for your interest!

[tmulcahy@salud.unm.edu]

Certainly, from one perspective, it looks like a classic statue bust. The face is not George Washington, although he seems to have been everywhere else, but it made me think that an alien race created the bust and set it spinning though space as a tribute to one of their great people.

[Chris Peterson]

Comet nucleus 67P, clearly enough, is not a binary object but a monolith with parallel primary layering in the upper and lower lobes, and the ”neck”.

Well, no. I'd say that's not clear at all.

Comet nucleus 67P – just as asteroid Itokawa (Geologi 2/2011, pp. 44-48) – appears to be a chunk of planet-scale oceanic crust, likely torn off Proto-Earth in the collision with Proto-Moon some 4.5 billion years ago.

There's really no evidence to support that claim (nor for Itokawa). What things look like is very different from what their chemistry tells us.

[Kaarlo]

Chris hi!
1. What's your proof for 67P being contact binary intsead of monolith?
How would you explain parallel structures (such as layering and consistently cross-cutting dyke swarms) in and through the lobes and the neck?
2. The Itokawa sample collector grossly failed but succeeded to bring back a few dust grains of basaltic composition - a rock type typically found in terrestrial Mid Ocean Ridge environments.
How would you explain the existence of pillow lava on Itokawa? - see Figs. 7 and 8 in http://www.geologinenseura.fi/geologi-l ... Makela.pdf

[Kaarlo]

Chris, here's the correct address, Kaarlo.
See Figs. 7 and 8 in http://www.geologinenseura.fi/geologi-l ... Makela.pdf

[neufer]

Comet nucleus 67P – just as asteroid Itokawa (Geologi 2/2011, pp. 44-48) – appears to be a chunk of planet-scale oceanic crust, likely torn off Proto-Earth in the collision with Proto-Moon some 4.5 billion years ago.

There's really no evidence to support that claim (nor for Itokawa). What things look like is very different from what their chemistry tells us.

The Itokawa sample collector grossly failed but succeeded to bring back a few dust grains of basaltic composition - a rock type typically found in terrestrial Mid Ocean Ridge environments.

---

Off on a Comet (French: Hector Servadac) is an 1877 science fiction novel by Jules Verne.

<<The story starts with a comet called Gallia, that touches the Earth in its flight and collects a few small chunks of it. The disaster occurred on January 1 of the year 188x in the area around Gibraltar. On the territory that was carried away by the comet there remained a total of thirty-six people of French, English, Spanish and Russian nationality. These people did not realize at first what had happened, and considered the collision an earthquake. They first noticed weight loss: Captain Servadac's adjutant Ben Zoof to his amazement, jumped twelve meters high. Zoof with Servadac also soon noticed that the alternation of day and night is shortened to six hours, that east and west changed sides, and that water begins to boil at 66 degrees Celsius, from which they rightly deduced that atmosphere became thinner and pressure dropped. At the beginning of their stay in Gallia they noticed the Earth with the Moon, but thought it was an unknown planet. Other important information was obtained through their research expedition with a ship, which the comet also took. During the voyage they discovered a mountain chain blocking the sea, which they initially considered to be the Mediterranean Sea and then they found the island of Formentera (before the catastrophe a part of the Balearic Islands), where they found a French astronomer Palmyrin Rosette, who helped them to solve all the mysterious phenomena. They were all on the comet which was discovered by Rosette a year ago and predicted a collision course with Earth, but no one believed the astronomer, because a layer of thick fog at the time prevented astronomical observations in other places.

As found by a new research expedition, the circumference of Gallia was 2320 km.

Involuntary travelers through the Solar system did not have any hope for long-term colonization of their new world, because they were lacking arable land. They ate mainly the animals that were left on the land carried away by Gallia. One strange phenomenon, they met was that the sea on the comet did not freeze, even though the temperature dropped below the freezing point (theory that the stationary water level resists freezing level for longer than when a rippled by wind). Once a stone was thrown into the sea, the sea froze in a few moments. The ice was completely smooth and allowed skating and sleigh sailing.

Gallia got to an extreme point of its orbit and then began its return to Earth. In early November Rosete's refined calculations showed that there will be a new collision with the Earth, exactly two years after the first, again on January 1. Therefore, the idea appeared to leave the comet collision in a balloon. The proposal was approved and the castaways made a balloon out of the sails of their ship. In mid-December there was an earthquake, in which Gallia partially fell apart and lost a fragment, which probably killed all Englishmen in Ceuta and Gibraltar. When on January 1 there was again a contact between the atmospheres of Gallia and Earth, the space castaways left in the balloon and landed safely two kilometers from Mostaganem in Algeria.>>

[Chris Peterson]

Chris, here's the correct address, Kaarlo.
See Figs. 7 and 8 in http://www.geologinenseura.fi/geologi-l ... Makela.pdf

Yes. I already read it. That was the reason for my reference about how things looked, versus their chemistry.

[Chris Peterson]

Chris hi!
1. What's your proof for 67P being contact binary intsead of monolith?

As a scientist, I never consider proof. Only evidence. I observe that structures like 67P are apparently common. I observe that paired asteroids are apparently common. I observe that dynamical simulations show how these form, and how contact binaries form from them. I note that a simple process that we understand and anticipate provides a better explanation than a complex one involving the ejection of material from Earth's gravity well while maintaining structure.

How would you explain parallel structures (such as layering and consistently cross-cutting dyke swarms) in and through the lobes and the neck?

First, I a prefer a lack of explanation at all to a contrived explanation. I would avoid constructs like "cross-cutting dyke swarms" which are already over-interpreted given the existing evidence. I would be extremely cautious about comparing the morphology of terrestrial planet structures with those observed on ice-stone bodies just a few kilometers across.

2. The Itokawa sample collector grossly failed but succeeded to bring back a few dust grains of basaltic composition - a rock type typically found in terrestrial Mid Ocean Ridge environments.

Basaltic composition is commonly found in many meteorites, particularly the eucrites that probably derive from Vesta- an asteroid that certainly did not originate on Earth. Basaltic composition is not adequate to demonstrate an Earth origin.

How would you explain the existence of pillow lava on Itokawa? - see Figs. 7 and 8 in http://www.geologinenseura.fi/geologi-l ... Makela.pdf

First I'd need to be convinced that there was pillow lava on Itokawa. Superficially similar appearance does not meet my own standards of evidence.

[beefcalf]

Kaarlo,
In linked PDFs authored by you, you reference Richard B. Hoover's paper 'Fossils of Cyanobacteria in CI1 Carbonaceous Meteorites'.

My initial curiosity over your surprising interpretation has been replaced with resignation. If either you or the engineer Mr. Hoover would like your ideas to be taken seriously, getting published in a respected, peer-reviewed journal will do much to achieve that goal.

[Kaarlo]

OK, Chris, I admit: I'm being a bit provocative on purpose - sorry about that - but it worked.
This is not the first - and likely not the last - time a geologist finds it difficult to communicate with astronomer: we lack common language.
For example, you explain contact binaries hypotethically, with physics and/or mathematics (am I right?) - while I explain, in terms of geology, WHAT I ACTUALLY SEE.
Yeah, its a pity the sampler failed to bring the lava pillow from Itokawa. I just wonder if you had taken a solid rock as evidence.
By the way: how would you explain the intense folding of strata on Vesta - say - with astronomical tems?

[Chris Peterson]

OK, Chris, I admit: I'm being a bit provocative on purpose - sorry about that - but it worked.
This is not the first - and likely not the last - time a geologist finds it difficult to communicate with astronomer: we lack common language.
For example, you explain contact binaries hypotethically, with physics and/or mathematics (am I right?) - while I explain, in terms of geology, WHAT I ACTUALLY SEE.
Yeah, its a pity the sampler failed to bring the lava pillow from Itokawa. I just wonder if you had taken a solid rock as evidence. :ssmile:
By the way: how would you explain the intense folding of strata on Vesta - say - with astronomical tems?

As it happens, I'm also a trained geologist, which is one reason I'm extremely cautious about drawing inferences based on nothing more than apparent morphology.

[Kaarlo]

Fine! Pleased to find a colleague! However, take my friendly advice: start thinking like one.
With astronomers' overcautious attitude science will "never" advance.

[Chris Peterson]

Fine! Pleased to find a colleague! However, take my friendly advice: start thinking like one.
With astronomers' overcautious attitude science will "never" advance.

Skepticism and caution are at the core of science. Science advances because of them.

A scientist says "That structure on Itokawa looks like pillow lava. How can we explain that?" A pseudoscientist says "There is pillow lava on Itokawa, which is evidence the asteroid has a terrestrial origin."

[Kaarlo]

Well, then, Chris, the scientist: How can YOU explain the structure on Itokawa - the one that looks like pillow lava? (no irony, just collegial curiosity)

[Chris Peterson]

Well, then, Chris, the scientist: How can YOU explain the structure on Itokawa - the one that looks like pillow lava? (no irony, just collegial curiosity)

I can't explain it. But I don't see that as requiring some ad hoc explanation. Science starts with questions, and works because we don't require answers before we can effectively provide them. There's such a thing as simply lacking enough information to provide answers with any degree of certainty.

[tao]

This will be a bit of a threadjck, but I can't resist:
Where is the Millenium Falcon?

SW The Empire Strikes Back - asteroid field scene
(specifically, the asteroid seen rotating on minute 2:17)

[chuckster]

With all the discussion here of -apparent- features, I as a layman, had a question. From Rosetta photos of the bleak landscape of this object, that it took just prior to its touchdown, it -looked- like there were scree slopes below cliffs. Is there enough gravity on this comet for rocks to fall off cliffs and form fans of loose rocks at their base, or is that just my Earthman's eyes interpreting a feature that is just a leftover from the surface evaporating in sunlight ?

[neufer]

With all the discussion here of -apparent- features, I as a layman, had a question. From Rosetta photos of the bleak landscape of this object, that it took just prior to its touchdown, it -looked- like there were scree slopes below cliffs. Is there enough gravity on this comet for rocks to fall off cliffs and form fans of loose rocks at their base, or is that just my Earthman's eyes interpreting a feature that is just a leftover from the surface evaporating in sunlight ?

Hard objects like rocks are pretty much going to act like they would on Earth except ~200 times slower. Your falling rock will hit other rocks much more slowly but those rocks will be much easier to dislodge due to the low gravity. And a pile of dry sand should have roughly the same "slip face" angle.

[JohnD]

Kaarlo,
Anyone can have their opinion, deluded on not, but when a 'trained geologist' misuses their expertise, to be provocative and to get a reaction on serious scientific message board - that just pathetic. You could have got a reaction by discussing the points made here by others, asking, pleading for explanation of extra-ordinary sights, but you played the fool.

Neufer,
NASA looked at 'angle of repose' rather than slip angle: http://shadow.eas.gatech.edu/~cpaty/cou ... ravity.pdf

Difference not great but is real, it appears,

John

[neufer]

Neufer,

NASA looked at 'angle of repose' rather than slip angle:
http://shadow.eas.gatech.edu/~cpaty/cou ... ravity.pdf

Difference not great but is real, it appears,

• My initial response (off the top of my head just like Chris does!)
  was not great but it was sorta real...so I won't bother to repost.

Static and dynamic angles of repose in loose granular materials under reduced gravity

by M. G. Kleinhans, H. Markies, S. J. de Vet, A. C. int Veld, and F. N. Postema.
Received 30 May 2011; published [JGR] 17 November 2011.

<<Granular materials avalanche when a static angle of repose is exceeded and freeze
at a dynamic angle of repose. Such avalanches occur subaerially on steep hillslopes and
wind dunes and subaqueously at the lee side of deltas. Until now it has been assumed that
the angles of repose are independent of gravitational acceleration. The objective of this
work is to experimentally determine whether the angles of repose depend on gravity.

For all materials, the static angle of repose increases about 5° with reduced gravity,
whereas the dynamic angle decreases with about 10°. Consequently, the avalanche size
increases with reduced gravity. The experimental results suggest that relatively low slopes
of granular material on Mars may have formed by dry flows without a lubricating fluid.
On asteroids even lower slopes are expected. The dependence on gravity of angle of
repose may require reanalysis of models for many phenomena involving sediment,
also at much lower slope angles.>>