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Asteroid approach, Science operations begin!
Daniele_bianchin...
post Apr 14 2019, 09:03 AM
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This revolutionizes a bit how I imagined the surface of asteroids forever and how we all imagined it, I think. It does not seem something anomalous or alien but something very common, any valley of terrestrial stones that is often found in the high mountains. I am trying to imagine the men in scale in these photos, exploring among those numerous rocks and I realize that there are so many that it would be difficult to walk there. So many "common" rocks let me think of the remains a part of an already existing and exploded world rather than an agglomeration formed with millions and millions of years. I probably can't conceive.
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Marcin600
post Apr 15 2019, 10:17 PM
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"Benben" - largest boulder on Bennu: https://www.asteroidmission.org/20190307-polycam-benben/

(I found in reliable Wikipedia: "Benben was the mound that arose from the primordial waters Nu upon which the creator deity Atum settled in the creation myth of the Heliopolitan form of ancient Egyptian religion. The Benben stone (also known as a pyramidion) is the top stone of the pyramid. It is also related to the Obelisk." - https://en.wikipedia.org/wiki/Benben

And for fun, and for scale - a brave future astronaut exploring this huge rock with pickax wink.gif
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Marcin600
post Apr 16 2019, 01:29 AM
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QUOTE (Daniele_bianchino_Italy @ Apr 14 2019, 11:03 AM) *
This revolutionizes a bit how I imagined the surface of asteroids forever and how we all imagined it, I think. It does not seem something anomalous or alien but something very common, any valley of terrestrial stones that is often found in the high mountains. I am trying to imagine the men in scale in these photos, exploring among those numerous rocks and I realize that there are so many that it would be difficult to walk there. So many "common" rocks let me think of the remains a part of an already existing and exploded world rather than an agglomeration formed with millions and millions of years. I probably can't conceive.
[]

"So many "common" rocks let me think of the remains a part of an already existing and exploded world rather than an agglomeration formed with millions and millions of years."

In the case of Ryugu, according to this article in Science, one of the models of its origin assumes that it (or rather its parent body) was broken into pieces by catastrophic impact and reaccumulated, at least a couple of times! Maybe the same applies to Bennu (?)
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AndyG
post Apr 16 2019, 10:36 PM
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I need help here.

I can see a protoplanetary disc containing silicon and oxygen, and I can see these elements combining to make molecules that may later join together to form rock-dust-bunnies, bonded by electrostatic forces.

Here on Bennu I'm looking at consolidated rocks, alongside other 'conglomerates' that do not appear, at least at first glance, as particularly rock-like.

What is the step from dust to solid rock? Does it imply gravity (there's precious little here), heat from impacts (but, then, what keeps the dust together in such a collision?)

How does it potentially occur?

Andy

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Marcin600
post Apr 16 2019, 11:26 PM
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QUOTE (AndyG @ Apr 17 2019, 12:36 AM) *
I need help here.

I can see a protoplanetary disc containing silicon and oxygen, and I can see these elements combining to make molecules that may later join together to form rock-dust-bunnies, bonded by electrostatic forces.

Here on Bennu I'm looking at consolidated rocks, alongside other 'conglomerates' that do not appear, at least at first glance, as particularly rock-like.

What is the step from dust to solid rock? Does it imply gravity (there's precious little here), heat from impacts (but, then, what keeps the dust together in such a collision?)

How does it potentially occur?

Andy


Remember that small rocky asteroids like Bennu or Ryugu are not substantially primordial bodies, but formed from the breakdown of much, much larger asteroids. On these larger parent bodies (primordial), gravity was much higher, impact resistance was greater and, at the beginning, there was a lot of heat from the decomposition of short-lived elements, like aluminium (aluminum smile.gif isotope Al26
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Marcin600
post Apr 16 2019, 11:34 PM
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As far as I know, the details of the transition "from dust to rocks" are not well known (?) and it is being investigated (and its vision changes) before our eyes! The only "truly" primordial object we have seen so far is Ultima Thule, but it has a different composition (a lot of "ice"), because it is located (and always was there) far from the Sun.
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alan
post Apr 17 2019, 08:44 PM
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The popular model these days is that in the protoplanetary disk dust grews into pebbles, probably mm sized in the inner solar system. In some parts of the disk these be came concentrated enough by one of a variety of of mechanisms to undergo a gravitational instability which caused clumps of them to collapse into asteroids ~100km in diameter. The consolidated rocks would form in these asteroids and be broken up and scattered in later collisions.
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JRehling
post Apr 18 2019, 01:53 AM
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My understanding, via meteorites:

Parent bodies were either differentiated (large enough to have possessed sufficient radiogenic heat to melt) or not. From those that were smaller, we have chondrites, whose solid minerals date back to the first millions of years after the origin of the solar system. Chondrites have iron in abundance along with other stone – a lot like the overall composition of the Earth or Venus if you count the cores and mantles both – but in the chondrites, iron and stone are mixed on a fine level.

From larger parent bodies, exemplified near the larger end by Vesta, we have achondrites. Like smaller versions of the Earth and Venus, these were large enough to melt through, and their iron descended into a core, leaving a relatively iron-poor mantle/crust. Meteorites from Vesta therefore have elemental composition approximately like the crusts of Earth or Venus.

Bennu sure looks like some interesting geology has taken place, but it is classified as carbonaceous and is thus likely a fragment of a smaller, undifferentiated parent body rather than a larger one. If so, we'll expect to find higher levels of iron when we get those samples.

http://meteorites.wustl.edu/metcomp/index_files/image002.gif
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charborob
post May 10 2019, 02:05 AM
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Looking at the published images of Bennu (link), I noticed that two of them could be stitched together:
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Marcin600
post May 14 2019, 11:46 PM
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North side of Bennu's largest boulder (nicknamed Benben) - rotaded, brightened and with scale bar. In the third picture for scale is Apollo 12 astronaut Pete Conrad with Surveyor 3
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Marcin600
post May 15 2019, 12:45 AM
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And a bit more "free" version of this photo with Apollo 12 astronaut Pete Conrad with Surveyor 3 for scale
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climber
post May 15 2019, 08:08 PM
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Why did you choose the shortest men on the Moon? biggrin.gif


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Marcin600
post May 15 2019, 08:32 PM
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QUOTE (climber @ May 15 2019, 10:08 PM) *
Why did you choose the shortest men on the Moon? biggrin.gif


Because he was most photogenic wink.gif
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