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Mission: Hayabusa 2
pandaneko
post Today, 03:09 AM
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Something has been bothering me a lot. It is as follows.

If an asteroid is made of hard metal and somewhow it is covered with sands and pebbles and rocks and if someting collides with it very
hard resulting schock wave must be cataclysmic to shake them beyond escape velocity, leaving nothing but the metal asteroid.

Craters on Ryugu seem to suggest that Ryugu is like a metal, soft metal, soft enough to leave crater holes but hard enough not to break
up on impact. So, why are there regolith and boulders still left on Ryugu? Where did those boulders come from in the first place?

I am trying to persuade myself that those shaken off Ryugu travelled into deep space and came back to where they started from after
billions of years in the solar system. Am I going mad?

P
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Explorer1
post Today, 03:29 AM
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There's probably no metal at all in Ryugu, it's more of a 'rubble pile', of low density rocks (just like Itokawa), with many voids and empty spaces inside. I'd guess the inside is as broken and fractured as the surface the cameras can show us.
The craters we see are all very soft, with rounded edges, and every impact just breaks off more pieces, which either don't have enough velocity to escape and come back as boulders (I'd guess the enormous one at the pole is one), or, if they have enough velocity, fly off as separate bodies, permanently. The ones we see now were all probably part of the original body when it first broke off in turn from its parent body eons ago, and have just been broken up and reformed, probably many times since.

The impact projectile Hayabusa 2 is carrying is the perfect experiment to demonstrate this when they fire it at Ryugu. It should replicate the natural process on a smaller scale.
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wildespace
post Today, 06:22 AM
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QUOTE (Explorer1 @ Sep 23 2018, 04:29 AM) *
There's probably no metal at all in Ryugu, it's more of a 'rubble pile', of low density rocks (just like Itokawa), with many voids and empty spaces inside. I'd guess the inside is as broken and fractured as the surface the cameras can show us.
The craters we see are all very soft, with rounded edges, and every impact just breaks off more pieces, which either don't have enough velocity to escape and come back as boulders (I'd guess the enormous one at the pole is one), or, if they have enough velocity, fly off as separate bodies, permanently. The ones we see now were all probably part of the original body when it first broke off in turn from its parent body eons ago, and have just been broken up and reformed, probably many times since.

The impact projectile Hayabusa 2 is carrying is the perfect experiment to demonstrate this when they fire it at Ryugu. It should replicate the natural process on a smaller scale.

Ryugu's extremely low gravity probably corresponds to it being a rocky rubble pile. If it were a solid metal asteroid, it would have a much stronger density and gravity, right?


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OrbitrapInSpace
post Today, 10:28 AM
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QUOTE (pandaneko @ Sep 23 2018, 05:09 AM) *
If an asteroid is made of hard metal and somewhow it is covered with sands and pebbles and rocks and if someting collides with it very
hard resulting schock wave must be cataclysmic to shake them beyond escape velocity, leaving nothing but the metal asteroid.


the collision will result in huge fragmentation, generating a kind of cloud of material, which will collide each other and dissipate the energy, to the point their relative speed is reduced and accretion starts again.

close observation of Ryugu and its reaction to the impactor is hence part of the evaluation of the theoretical descriptions.

Patrick Michel is part of the Hayabusa scientific team, and he is an expert in simulation of such processes,

movies illustrating the various mechanisms here : simulations of asteroid collisions

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pandaneko
post Today, 11:51 AM
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QUOTE (OrbitrapInSpace @ Sep 23 2018, 07:28 PM) *
the collision will result in huge fragmentation, generating a kind of cloud of material, which will collide each other and dissipate the energy, to the point their relative speed is reduced and accretion starts again.

movies illustrating the various mechanisms here : simulations of asteroid collisions


OrbitrapInSpace , thank you for this. My thinking was too simplistic. I would have thought that all bits and pieces on the asteroid surface
will move in the same way upon impact, each with enough escape velocity. Mutual collisions in confusion after impact leading to energy
dissipation, no, never thought about it that way.

My guess is that they will then fall into an equilibrium state for some time, just like gas molecules in a container, forming, presumably
clouds around the asteroid, then eventually falling back down to its surface, making up regolith and boulders as we see now.

Yes, it makes sense.

P



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