Starship Asterisk*

please select an alternative wrote: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 wrote: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”.

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.

Kaarlo wrote:

Chris Peterson wrote:

Kaarlo wrote:
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.

https://en.wikipedia.org/wiki/Off_on_a_Comet wrote:

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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.>>

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

Kaarlo wrote: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 wrote: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?

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

Kaarlo wrote: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)

chuckster wrote:
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 ?

JohnD wrote:
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.

http://tinyurl.com/gtnxjzz wrote:
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.>>