And yet scientists and designers of Hayabusa 2 seemed quite surprised by the lack / deficiency of the smallest particles of regolith (dust and sand) on Ryugu's surface.
If the mechanism you describe works, and at least some of the small asteroids are considered a pile of debris, then one can expect that the smaller the asteroid, the larger the rocks on the surface. I am curious about the results from OSIRIS-REx at Bennu. A lot of explanations will also bring results from MASCOT if they finally appear. The copper projectile will also tell a lot about Ryugu's surface. And of course, with a bit of luck, the content of the return capsule - but it still requires a lot of patience...

Impact ejecta particles will have a wide range of velocities. Look at Tycho crater on the Moon, where some ejecta can travel across much of the near side of the Moon, or even possibly converge on its antipode, but much more of it by volume was only just able to get out of the crater and covered the surface as a thick continuous ejecta blanket. Some didn't even get out and slumped back into the crater. On Ryugu, some ejecta might fly out at escape volocity, but some impact energy goes into jostling the blocks near the impact, breaking them into smaller pieces and no doubt generating dust in the process. There should be dust, and impacts cannot preferentially remove it as ejecta.

Large particles are often observed to collect at the top of a container of mixed particle sizes (the 'brazil nut effect'). The chances are that there is plenty of dust on Ryugu, but the bigger chunks are concentrated at the surface and the dust drains down into the voids between them. I think that is what we are seeing at Ryugu. We woild only need a very thin layer of it on the surface blocks to produce a visible effect when thrusters blow it away, and that amount would not be visible in the kind of images we have been seeing of the surface.

Phil

I agree with you, Phil, that "BNF" (I mean the "Brazil Nuts Effect") is a good candidate to explain the situation on the surface of Ryugu.
But, as a complete amateur, I have two questions:
1. Does "BNF" operate without gravity or in very low gravity as on Ryugu?
2. Does "BNF" work without "walls of the container" (as on Ryugu)?

I also remember that even on such a large globe as the Moon, dust can electrostatically levitate just above the surface - contrary to the force of quite high gravity, and therefore, potentially against the settling in the voids in the depths of the asteroid too.

Marcin

press release in english.
http://fanfun.jaxa.jp/jaxatv/files/20190305_hayabusa2_en.pdf

https://www.youtube.com/watch?v=-3hO58HFa1M

I updated the map of Ryugu with information from the new press release - may I say here how great the Hayabusa 2 press releases have been, just incredibly informative and detailed.

Phil

I didn't realize that the impactor is going to target poor Mascot, more or less...

Astounding views of the sampling! Looks like plenty of debris could have gone into the funnel. Looks like some pieces hit the side of the spacecraft too, judging from the video.
Hard to believe, but the SCI impact next month will be even more impressive (from a safe distance!).

It appears from the press release that they may still release the final rover this summer. Even if it's not working properly, surely there's not point in lugging that mass back to Earth.

one question comes to my mind after seeing the video, that I have not seen addressed: are all of the flying debris still gravitationally bound to Ryugu? will they fall back on it? will they end up in orbit? are we witnessing the birth of a mini-moon? or, finally, will they end in separate solar orbit?

Why is it that the same fragments look shiny and then dark as they fly up rotating?

P

Almost all of the fragments will either have escape velocity and disappear or not quite enough and settle back on the surface. A single kick from the surface can put an object into orbit but this orbit will have a perigee that is the same as the point it was kick off the surface. To go into a stable orbit it needs a second kick at some altitude above the surface to raise it perigee off the asteroids surface. The escape velocity is about 0.38m/s or about 1.35 km/h. This is one of the reasons why a cannon shell can not be fired into a stable orbit.


Id say some are sun illuminated and some in shadow

Yes. I'm mentally trying to calculate if slower-moving particles ejected in the initial impact could provide such a second kick to (returning) higher-speed ejecta. Higher speed here being less than the 0.38 m/s escape velocity.

Must be a tiny amount of the total ejected material put into such an orbit.

Andy

what do you think the bright spot is?

The target marker? Looks like the right area based on the new maps...

And yet some dust probably (from: https://www.youtube.com/watch?v=-3hO58HFa1M)

floating piece of gravel - quite flat