Asteroid approach, Science operations begin! Options

[Quetzalcoatl]

Bennu originated as a fragment of a larger body, so both the breakup event and the possible forces within the parent body seem to be more likely sources of fractures than anything that would occur in a body the size of Bennu.

Good morning JRehling,

I had come to make this assumption, namely that these fractures and geometric forms did not come from in-situ processes but, more probably, were prior to the formation of Bennu, resulting from events having occurred on a parent body, The scars of an ancestor, I might say.

But my modest level of knowledge in this area is greatly enhanced by your expertise. Thank you.

[Marcin600]

Since „...the most prominent joints occur [on Earth] in the most well-consolidated, lithified, and highly competent rocks, such as sandstone, limestone, quartzite, and granite...” (Wikipedia: Joint in geology), I think we can say - at least - that these two specific boulders (rock fragments) on Bennu are quite compact, and not „fluffy”, like most boulders on Ryugu. But such rocks on Bennu are probably an exception, because so far only very few such geometric cracks have been photographed (?)

I'm not geologist, but I would bet on thermal stress for the reasons for these cracks.

Alternatively, it may have something to do with generating of stresses in rocks during collisions (impacts) - - maybe even on the parent body (although this second stone seems to have broken quite "recently" - on a cosmic time scale).

[Quetzalcoatl]

Hello Marcin,

Some remarks to explain my point of view :

The object of my curiosity concerns the geometric shapes on the scale of the meter with two images that you had posted, namely a large straight fracture and what seems to me to be relatively flat surfaces with right angles.

Significant differences in daytime and nighttime T° can certainly cause rock fractures. But I’d be surprised if that were the case here, for a straight fracture approximately three metres long.

Even more, on the second image that I had selected, what appears as flat surfaces seen from above (Strata?) with right angles do not seem to me to be able to be explained by thermal, mechanical processes (impact) or others affecting an asteroid with a gravity as low as Bennu.

My advice is given with caution, because I know very little.

[Marcin600]

Quetzalcoatl, are you suggesting some sort of bedding on Bennu or his perent body? That would be an interesting issue.

For me, these rectangular forms and flat plates on this little asteroid are quite mysterious, but - as I wrote - I am not a specialist...

On the other hand, on comets, such as Churyumov-Gerasimenko, we have a fractal structure: from microcrystals, through crystals to very large structures - everything reflects the original way of forming. Maybe in these two boulders on Bennu we actually see some "huge, original crystal structure", but it seems to me quite unlikely...

I think the biggest problem is that we really know very little about the nature of these rocks, their structure, origin, mechanical properties, mineralogical composition, etc. That is why we need samples of Bennu rocks in Earth's labs so much. Having them in our hands (with a little luck there will also be tiny fragments similar in properties to these interesting boulders) we will solve many puzzles.

From Wikipedia - Orthogonal joint sets on a bedding plane in flagstones, Caithness, Scotland, Earth and negative picture:

Attached thumbnail(s)

 

[Quetzalcoatl]

Quetzalcoatl, are you suggesting some sort of bedding on Bennu or his perent body? That would be an interesting issue.

For me, these rectangular forms and flat plates on this little asteroid are quite mysterious, but - as I wrote - I am not a specialist...

In any case, that is what I seem to see, in view of this image alone.

It would take others, taken in a more razing way to know exactly the shape of what is hidden under this flat surface. The thickness of what I think is a plate, a sheet, could be an element of a originally layered rock structure. If this were true, an exogenous origin in Ryugu would be, in my opinion, unquestionable. But these are speculations, I readily admit.

Mini-landers Minerva of the type Hayabusa 2 had dropped on Itokawa could have done wonders to examine closely the rocks of Ryugu. However, the possible rarity of the rock examples we are talking about here would certainly have made the desired observations very unlikely.

[Quetzalcoatl]

On the other hand, on comets, such as Churyumov-Gerasimenko, we have a fractal structure: from microcrystals, through crystals to very large structures - everything reflects the original way of forming. Maybe in these two boulders on Bennu we actually see some "huge, original crystal structure", but it seems to me quite unlikely...

I am often reserved enough to compare the geological characteristics of what we observe on asteroids with terrestrial examples. The physical conditions are too different. To a lesser degree, the similarities between cometary and asteroid surfaces must certainly be done with caution. I won’t say any more.

[Quetzalcoatl]

I think the biggest problem is that we really know very little about the nature of these rocks, their structure, origin, mechanical properties, mineralogical composition, etc. That is why we need samples of Bennu rocks in Earth's labs so much. Having them in our hands (with a little luck there will also be tiny fragments similar in properties to these interesting boulders) we will solve many puzzles.

On that point, I completely join you. I am too impatient and it is very likely that the analysis of the samples will change our knowledge. They may also be able to shed light on our questions?...

[Marcin600]

Three days left until the first rehearsal

I wonder: can back-away burn at 75 m pick up any debris from Bennu's surface?

[Brian Swift]

Any OSIRIS-REx navigation people here?
I'm wondering if SPICE kernels with predicts for Tuesday's “Checkpoint” rehearsal are publicly available anywhere.
The kernels I looked at from NAIF don't appear to include the maneuver.

[mcaplinger]

The kernels I looked at from NAIF don't appear to include the maneuver.

I presume you looked at https://naif.jpl.nasa.gov/pub/naif/ORX/kern...-TR1P2-L_v1.bsp

I don't know what the TR1P2 maneuver is (TAG Rehearsal 1 Phasing 2?) but it's small and happened today, and that's the latest file out there. I'd check the mission status update on Monday to see if there are any new tidbits.

I don't know of a public site other than NAIF.

[Holder of the Tw...]

A "trim" maneuver would be named TRnTn (fill in the n with some number). Two similarly named adjustments were cancelled according to this status report:

April 6 report

I'm not sure what a "P" maneuver would be. Maybe phasing like you suggested. They did mention phasing burns in the status report.

[Brian Swift]

I presume you looked at https://naif.jpl.nasa.gov/pub/naif/ORX/kern...-TR1P2-L_v1.bsp

Thanks Mike. Yup, that is what I'm looking at.

[mcaplinger]

A "trim" maneuver would be named TRnTn (fill in the n with some number).

I think the first letters are the mission phase, for example there was a maneuver R3R (Recon 3R?). Not sure what the second letter means, there have been P, R, D, T. But I could be wrong.

I'm sure this is documented somewhere, but my access to OREx documents is limited and I couldn't tell you if I knew for sure anyway, so I'm just speculating.

[mcaplinger]

I'm wondering if SPICE kernels with predicts for Tuesday's “Checkpoint” rehearsal are publicly available anywhere.

See if https://naif.jpl.nasa.gov/pub/naif/ORX/kern...-L-TR1BO_v1.bsp is what you're looking for.

[Marcin600]

Checkpoint rehearsal activities start today, April 14, at 2:45 pm EDT = 18:45 (6:45 pm) UTC - on twitter

Operations plan - pdf

Here is the current distance from Bennu - but I don't know how often it will be updated?