[X] My Assistant

[hendric]

Any speculation yet on the bright spot on the top? (north?) Exposed water ice seems unlikely at this distance from the sun! Maybe carbonates?

[Guest_mcmcmc_*]

Exposed water ice seems unlikely at this distance from the sun! Maybe carbonates?

I dont't get the connection.

[john_s]

Remember this object has very low albedo, so a "bright" spot could still be quite dark in absolute terms. For instance a chunk of lunar mare basalt would probably look bright if transported to Ryugu. To me it looks like a large boulder sitting at the pole- whether the higher albedo is due to exotic composition or just the exposure of a fresh, unweathered, rockface remains to be seen.

John

[dudley]

I was thinking of salt deposits, like those found in Occator crater on Ceres. I doubt, though, that such a small body as Ryugu would be geologically differentiated, so as to permit this.

[Paolo]

I am neither a chemist nor a geologist, but I think carbonates would require liquid water to form.
on the subject of the number of craters, on the latest image I can count only one bona fide crater, plus 3 or 4 suspect circular features, possibly subdued craters.

[marsbug]

If Ryugu turns out to be a fragment (or collection of fragments) from a larger body then water alteration processes might still have played a part in the history of it's rocks.

[Phil Stooke]

I'm very dubious about any supposedly bright spots on Ryugu. John mentioned just an unweathered rock face, which I agree with, and don't forget that in the low resolution images where the big rock first appeared, most pixels covered areas containing both sunlit and shadowed areas, so they look darker anyway. A rock big enough to have a completely unshadowed face might contain the only pixel or two with absolutely no shadows.

Phil

[john_s]

Not sure I agree about the shadows- the polar boulder (or whatever) was definitely brighter than the subsolar point when fully illuminated, and the subsolar point should also be shadow-free at the resolution of those approach images, especially at this low phase angle. Anyway, we'll know soon enough.

[Phil Stooke]

A very rough surface like this (thinking of high resolution images of Hayabusa, piles of loose rock fragments) will have shadows even at the sub-solar point if not seen at zero phase angle.

Phil

[Station]

Hi,

Does any of Hayabusa's minilanders/minirobots have camera onboard, so it can send some nice pictures from the surface?

Thanks in adv. for any info.

[Explorer1]

I believe they all do.

[Guest_mcmcmc_*]

Does any of Hayabusa's minilanders/minirobots have camera onboard, so it can send some nice pictures from the surface?

Plenty of cameras.

MINERVA-II:
http://mineta-lab.yz.yamagata-u.ac.jp/HAYABUSA2.html
http://www.dlr.de/pf/Portaldata/6/Resource...oshimitsu_T.pdf
http://www.astro.mech.tohoku.ac.jp/~nagaok...iras_knaga1.pdf

MASCOT:
https://www.colorado.edu/event/ippw2018/sit...ot_ippw2018.pdf
https://elib.dlr.de/86421/1/reill_2824197.pdf

[pandaneko]

I watched through this one hour+ press question time video. There was not much we do not know
from other earlier information.

One thing catched my ears. It is about polar regions and naturally there were questions from
the press, including a few questions about the big boulder like thing at the north pole, if H2
will be exploring polar regions.

Prof Yoshikawa's answer was positive, but it seemed to me from the tone of his voice that JAXA
will be very uncomfortable to move H2 from the 20km parking position unless there are
scientifically good reasons.

If I remember correctly, H2 will have to move up in order to look at polar regions. If they go up
then they will have to inch back down to the parking height again, that sort of thing...

Another thing that was new to me, even if it should not be, was that H2's descent is actually still
part of catching up with Ryugu from behind. Once H2 reaches the parking position behind Ryugu
Ryugu will be rotating retrograde in front of H2, with its panells behind H2 facing the sun.

JAXA apparently want to keep that position as long as they can afford it. I think it is a kind of
vantage position with full energy supply from behind and Ryugu right in front.

P

[Guest_mcmcmc_*]

Wouldn't it be much easier landing on a static pole rather than on a moving equator?
Although linear speed of the surface of a 450-meters radius body fully rotating in 7.5 hours should be just 10 cm/s, why trying to sync H2 speed to surface speed and to avoid incoming rocks? A little rocks hitting the sampler at a few cm/s would apply a torque which would make H2 start rotating on its horizontal axis.
A big rock hitting H2 at 20 cm/2 would "pass" to H2 enough speed to cross escape velocity?!?


My math:
Frequency = F = 1 round in 7.5h = 1 round in 27000 s
Radius = R = 450m
Linear speed = V = W * R
W = 2*pi*F

V = 2 *pi * 1/27000 * 450 = 0,10 m/s

[pandaneko]

I now remember something else from this YT movie. A woman reporter asked about landing sites.

Prof said that they would choose areas free from boulders with size 1 meter or larger across
because sampler horn is one meter long and even suggested landing in a crater to avoid boulders.

P