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?

Click to view attachment

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

I don't think seismic effects would be size-selective. If the ground motion launches fine-grain stuff to escape velocity, it should launch coarser rocks too, no?

I could believe, though, that fine dust might be susceptible to electrostatic levitation if photoelectric charging or some other mechanism applies, as I think has been speculated for the moon. That sort of effect might cause small asteroids in particular to be relatively dust free.

(and there's the Brazil nut effect as well)

Undoubtably true if they all receive the same acceleration in a single impulse. But intuitively you would expect finer stuff to drift away more easily as a result of agitation, so is this a case where common sense turns out to be plain wrong or could there be something more to it? I'm wondering if the differently sized debris particles could 'thermalise' in the sense of sharing their kinetic energy like gas molecules in an atmosphere. In that case of course the lighter ones do preferentially escape. Just wondering . . .

Firing is now set for 5th, according to this evening' TV news.

P

Brasil nut effect. Or perhaps "reverse Brasil nut effect" on the dark side?

The Reverse Brazil Nut Effect in Granular Flow: Nutty or Not? - Limor S. Spector - December 10, 2007



If there is a charged dust layer, you also have to account for the "Cat-Styrofoam" effect...



A large object such as an asteroid (or cat) exposed to small particles which develop a charge such as dust (or styrofoam) will develop an opposite charge that prevents removal of the outer coating from the larger object.

An interesting concept is buried in a footnote-
What if the Brasil nut effect is dependant on relative temperature? (i.e. entropy, enthalpy, gibbs free energy)

If bulk temperature triggers a phase change in a rubble pile body from "brazil nut effect" (coarse grains move to the surface) to "reverse brazil nut effect" (fine grains move to the surface) then we have a brand new mechanism for comet evolution.

Reverse Brazil Nut Problem

A paper by Hong et al. in 2001 predicted the "reverse Brazil nut effect", in which under certain conditions, their numerical observation showed the opposite effect - large beads falling to the bottom of a container, and small beads rising to the top of the container. [4,5] A previous finding of theirs showed that a system of hard sphere condenses in the presence of gravity below a critical temperature Tc [6]- ] P.V. Quinn and D.C. Hong, Phys. Rev. E 62, 8295 (2000).
...
This means that if the diameter ratio is smaller than the inverse of the density ratio, the particle mixture should show Brazil-nut effect, but if the diameter ratio is larger than the inverse of the density ratio, the particle mixtures should show the reverse Brazil nut effect.

A different perspective of Otohime saxum & the South pole

From paper materials of http://science.sciencemag.org/content/earl...science.aaw0422

at http://www.darts.isas.jaxa.jp/pub/hayabusa...er/Sugita_2019/

Original image http://www.darts.isas.jaxa.jp/pub/hayabusa...748_tvf_l2b.tif

Click to view attachment

I remember my post from August 7, 2018 (above) - on first close-up picture of Ryugu’s surface I guessed presence of layers. In current Science article, cited above by bsharp http://science.sciencemag.org/content/sci/...aw0422.full.pdf, it turned out there are layers. But not in regolith, as I thought at the time, only in boulders:

Fig. 4C: "A Type 1 boulder, which is dark and rugged ... A close up of its layered structure is shown in fig. S11D" and

Fig. 7B: " A rugged boulder with layered structure (small yellow arrows) near the MASCOT landing site (9 mm/pix ...)".

These layers seem quite interesting to me. This is the impact breccia

JAXA plans to blow a copper projectile (creating an "artificial" crater) on April 5 - in a week!
Very detailed description in English (pages 12 to 23): http://www.hayabusa2.jaxa.jp/en/enjoy/mate...318_ver8_EN.pdf

Descent starting now!

Great summary from Jason Davis of PS, including timeline, and what images to expect: http://www.planetary.org/blogs/jason-davis...abusa2-sci.html

~30 minutes until Hayabusa2 partially avenges the dinosaurs and bombs an asteroid (not my quote)

Live YouTube telecast from the Hayabusa2 control room with English commentary link

Crater formation confirmed by JAXA>

P

picture of a separated SCI: https://twitter.com/haya2_jaxa

"...Image taken with the wide-angle optical navigation camera (ONC-W1) immediately after separating the SCI device (collision device) (after a few seconds). The reflective sheet attached to the SCI shines white because it has been photographed with a flash. It turned out that it was separated according to the schedule..."

" The deployable camera, DCAM3, successfully photographed the ejector from when the SCI collided with Ryugu’s surface. This is the world’s first collision experiment with an asteroid! In the future, we will examine the crater formed and how the ejector dispersed. " : https://twitter.com/haya2_jaxa

The moment of hitting an asteroid. Congratulations JAXA!

I brightened the picture a little

https://twitter.com/haya2_jaxa

The picture looks like expected (from an analog camera). It looks like the impact was slightly at an angle

There's been reporting that this image was from an analog camera, but that surely can't be correct since a vidicon tube would certainly be bulkier and heavier than a chip sensor!

It sounds like this image was from DCAM3, which (apart from an addional 2000x2000 pixel higher resolution sensor) is a duplicate of the DCAMs used on IKAROS. According to this page these encoded the signal as analog NTSC for transmission to the mother ship, hence the origin of "analog".

That same page lists the specs of the DCAM "analog" sensor, eg 656 x 492 pixel sensor size.

I also think that JAXA used the misleading terminology (in English) and the word "analog" only applies to signal transmission and not to image recording.

I can not find anywhere when we can expect photos from a 2000 x 2000 pixel sensor? (I found only the term "later") They should be very interesting! If they were well framed, of course

" ~30 minutes until Hayabusa2 partially avenges the dinosaurs and bombs an asteroid (not my quote)"


May Ryugu never take revenge on us in the future by hitting Earth
(and yet it would be beautiful pictures from space )

Here's everything you could ask for about DCAM3's 2 cameras:


Regarding the photos, they exist, but they seem to be holding them close to the vest for now.

Thanks for the references, Emily. They usually refer to DCAM3-A as the "analog imaging system" or the like, rather than an analog imager, which seems more accurate. (Pedantically speaking the pixel values of the CMOS are analog at an early stage...)

Thank you very much, Emily, for explanations!

I am very curious about these "hidden" high resolution photos! I think this is one of the greatest moments of space exploration - at least in the study of small bodies (and I have to say: I'm a bit surprised by the relatively cold reception of JAXA's results on this forum - maybe everyone is waiting for these "better" photos? ). We are lucky at all: Ryugu, Bennu, Ultima Thule, Churyumov-Gerasimenko ... A really great time!

New press conference is planned for April 11, 15:30 Japanese time (JST) = 6:30 UTC. http://fanfun.jaxa.jp/jaxatv/detail/14224.html
"...During this briefing session we plan to explain the SCI operation carried out from 4 to 6 April...".
Maybe we'll see awaited pictures!

"relatively cold reception"

It's not really cold, it is just that we need images to heat us up. The mission as a whole has had a lot of attention here, and we are all, I hope, extremely happy with the amount of data and great presentations available to us. I hope we will have these new images very soon.

Phil

It was just my impression - probably wrong.

I did figure we would see images much slower than (nearest example) Deep Impact; I still have memories of that 2005 stream when that post-impact image was downlinked and the team scrambled to put it on the projected screen. With the Hayabusa 2 sticking around for further science, we just have to wait a bit longer...

There's now a "briefing session materials" PDF and Youtube video there, both in Japanese.

I don't speak Japanese at all, so I'm just extracting the prettiest pictures. Text is from Google Translate.

• Animation sequence "SCI taken by TIR" (stills on p13-14 of PDF) -- this is awesome
• Slide 16, "Image by analog system" (as animated GIF)
  
  • "Image about 2 seconds after SCI operation (image released at 4/5 press conference)"
  • "First public image after about 25 seconds from SCI operation"
    Click to view attachment
• Slide 17, "Image by a digital system", "About 185 seconds before SCI operation" (inset "SCI body")
  Click to view attachment
• Slide 18, "Image by a digital system", "About 3 seconds after SCI operation"
  Click to view attachment

Waiting for the publication of a separate photo (?), I enlarged this cropped from pdf.
Completely different from Tempel 1. Of course, Ryugu is not a comet, but in my opinion it is clear that there is little dust on the surface of this asteroid - no clear cloud of dust in the picture.

(Personally, I still feel a little hungry...)

I found this animated gif showing the sequence of impact from DCAM3 camera,

and information about joint meeting of OSIRIS REx and Hayabusa 2 planned for April 16 and 17

An interesting story from behind the scenes about cooperation and competition between Hayabusa 2 and OSIRIS-REx teams, especially the statement of Professor Seiji Sugita (in Japanese, but for non-Japanese readers translator helps to find meaning). I think it partly explains why we have to wait longer for the best photos.

Crater Search Operation (CRA2) is now in progress. On April 24 at 19:30 UTC the altitude of Hayabusa 2 was about 4500 m. The lowest point above Ryugu - 1.7 km - is to be reached on April 25 at around 2:16 UTC. The goal is to observe the newly created crater.

The Crater:

https://twitter.com/haya2e_jaxa/status/1121381085957509120

Now in 3D

https://twitter.com/moffmiyazaki/status/1121635270946775040

According to this JAXA tweet above: „...The exact size and shape of the artificial crater will be examined in detail in the future, but we can see that terrain of an area about 20m wide has changed...”

But according to this source : „...As a result of Hayabusa 2 observation from a height of 1.7 km from Ryugu, it was found that the topography was deformed like a hole over a diameter of 10 meters...”

So, the crater has a diameter of between 10 and 20 m.

It seems to me that in the left and upper part we can see something like a low crater wall (?). The lower and the right part of the crater (in the picture) was disturbed by the presence of large stones

I interpret that pair of remarks to mean that the crater diameter is about 10 m, with visible surface changes (ejecta or the opposite, a removal of dust) over a diameter of 20 m.

The English translation of the press conference slides from April 11 (not including the recent crater search images) is now up on the material page.

A new press conference is scheduled for May 9, 15:00 JST = 6:00 UTC http://fanfun.jaxa.jp/jaxatv/detail/14553.html

"...At this briefing session we will explain crater search operations conducted from April 23 to 25 and the prospects for future exploration activities based on crater search operations..."

Maybe we will learn more details (and photos ) about the crater and some preliminary conclusions from this very interesting experiment!

Apparently, according to a local newspaper here, there are 11 craters made, minimum is 6 m in diamter,
largest 12 m, a target marker will be dropped on 16th and there will be a few observation decent
down to 10 m, then landing is planned for late next month before the asteroid gets too hot.

P

Press conference slides PDF (in Japanese): http://fanfun.jaxa.jp/jaxatv/files/20190509_hayabusa2.pdf

Google translation of press conference pdf - page 17:

"Science of SCI collision experiment: Summary

• SCI collision to S01 area (about 25 m distance) was successful.

• Impact emission (ejector) was observed for several hundred seconds (image taken by DCAM3).
– In low gravity, the duration is longer (about 300 times above the ground).
– Ejector deposition in the S01 area is strongly suggested.

• A nearly circular landform change exceeding 10 m in diameter was identified (ONC-T image).
-Drilling crater shape: Depth about 2-3 m. Side wall surface looks smooth.
-Movement of rock mass (digging) and accompanying topography change can also be seen.
– Changes in surface reflectivity (darkening) can also be observed (verification required).
-It is possible to estimate the surface strength and surface age of Ryugu from the diameter (next page).

• The formation of secondary craters and movement of rock mass can be seen along the oval circumference * .
– It is presumed that it is due to the collision of fragments (forward fragments) scattered forward of SCI.

* Precisely, "the line of intersection of the front piece cone and the long surface at the apex of the SCI operating point"

Page 20:

"4. Future operation policy:
■ Concept of operation plan from May to July
• Currently, Ryugu is approaching the sun (perihelion is in September). Asteroid surface temperature is high from now on It is possible to land until the beginning of July.
• The terrain around the crater and the condition of the spacecraft have been scrutinized by the beginning of June, and in fact the end of June Decide whether to implement touchdown operation at the beginning of July.
• The target point for implementation is the location where there is an ejector (scattered material) from an artificial crater
Choose from the area. • The operation name is “Pinpoint Touchdown” (PPTD).
• Two or three low altitude descent observation operations will be implemented between May and June before PPTD operation.
in addition
To conduct detailed topographical observation of the landing candidate site and, depending on the situation, drop the target marker.
• First run: 5/14 to 5/16, Operation name: PPTD-TM1 (described later)
• Second time: the end of May, Operation name: To be determined
• Third time: First half of June, Operation name: To be determined"

And my unauthorized translation (via Google translator) of four pages: 10, 13, 15 and 16 from press conference pdf :

[fragment of press conference video showing the SCI test and formation of additional craters - 29:22 - 29:55]

my animated gif from JAXA press conference pdf (page 11)

my animated gif's from JAXA press conference pdf - pages 31 and 30:

"SCI collision area taken from home position with ONC-T:
- Before SCI collision - 2019-03-21 13:03 (Japan time) altitude 14 km
- After SCI collision - 2019-04-17 21:04 (Japan time), Altitude 19 km
- After SCI collision (explanatory diagram)"

(Image credit: JAXA, Tokyo University, Kochi University, Rikkyo University, Nagoya University, Chiba Inst. Of Tech., Meiji Univ., Aizu Univ., AIST)

and my animated gif from JAXA press conference pdf - page 14 [actually from press conference video - 25:34 - 27:13]

"Science of SCI collision experiment: Additional craters
Before and after the collision
Blink image for before and after comparison
Change is seen.
- Crater shape terrain formation (upper circle)
- Movement of rock mass (lower circle)"

(Image credit: JAXA, Tokyo University, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST).

[my note: I think that according to JAXA scientists these "secondary" craters were created as a result of impacts of debris from the SCI detonation in space. That's why we can not actually call them secondary craters]

Official English version of the 9 May press conference pdf is now available on Hayabusa2 site

Craters that I called "additional" in my previous posts were actually named "sub-craters".

And there is an interesting article on the Hayabusa2 website: "The western bulge of 162173 Ryugu formed as a result of rotationally driven deformation process"

[Nota bene: the first picture in this article above reminds me of my annotation to the photo of Ryugu, which I made last year in my post - blocked as suggesting a conspiracy theory Life is hard...]

PPTD-TM1 (Pinpoint Touchdown – Target Marker 1) operation is now in progress . The goal is to drop the marker near the new crater for a possible second landing (but: "...the decision to perform a second touchdown has not been finalized..."). The lowest point above the surface - 10 m - is to be reached on May 16, 11:58 JST = 02:58 UTC. So, there is a chance that we will see more detailed pictures of "the Crater"