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In the video of the touchdown of Hayabusa 2 (https://www.engadget.com/2019/03/06/hayabusa2-probe-ryugu-touchdown-video/) no debris is visible until touchdown. After that, there is a lot of it (though the shadows cast by individual pieces may bloat that count) - as the 'video' has few individual frames, i am unclear on whether i am actually seeing the same pieces of debris for consecutive frames, but i got the impression that most are moving in a non-radial (from the point of touchdown) direction. Some seem to be falling off the probe as it ascends? In the reflection on the probe itself (upper right quadrant) we can see that there is debris above the probe? Additionally there is no debris visible in the lower left quadrant of the screen? Some of the debris gets 'blow' across the surface? (I am putting question marks behind those statements because i am not sure whether my observations are due to compression artifacts, weird lighting condidtions etc)

What is the debris (i.e. what event precipitated it), and why is it moving so peculiarly?

According to my calculations (input: density 1500kg/m³, radius 500m) the gravity on Ryugu should be about 0.00004g, so i am having a hard time comprehending/imagining what is happening.

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  • $\begingroup$ The lighting is odd in that terrain seems illum from upper left, while craft shadow indicates illum from behind (behind camera and below frame). The camera (ONC onboard nav cam W2 wide angle side view [or W1 wide angle down view]) resolution is 1mm/pixel at 1m. $\endgroup$ – amI Mar 6 at 19:34
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The debris is being blasted away by the rocket exhaust.

enter image description here

In this view, a few frames before touchdown, the entire left side of the image is covered in rubble. That's the type of material that is blown away. The material that will be blown away is mostly in the shadow of the lander in this frame, so it's not visible.

It's not well visible beforehand because the resolution is not high enough to distinguish the smaller pieces.

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  • $\begingroup$ Sure, the whole thing is supposed to be rubble-ish, but the impact/blastoff should only move things radially, shouldnt it? $\endgroup$ – bukwyrm Mar 6 at 15:30
  • $\begingroup$ Ah, I see what you mean. $\endgroup$ – Hobbes Mar 6 at 15:33
  • $\begingroup$ The SMP (sampler) ejecta mostly goes up the horn (tube), and what is not captured at the top then falls from the tube as the craft ascends. There is a lip around the bottom of the tube that can retain some grains until the craft decellerates its ascent, at which point they too can be captured. $\endgroup$ – amI Mar 6 at 19:26

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