[X] My Assistant

[Phil Stooke]

Today's HAYABUSA
2005/10/27(JST)

Distance from Earth : 293,869,920 km
Distance from Itokawa : 3.4km
*The tour for a global mapping has been completed.
*Returned to the initial point of the HP.
*Detailed observations on sampling site candidates start.


Woo-hoo! Now let's see some closer images... please?

Phil

[jamescanvin]

...
*Detailed observations on sampling site candidates start.
Woo-hoo!  Now let's see some closer images... please? 

Phil

And while the're at it I wouldn't mind knowing where these sampling site candidates are too!

Pretty please?

James

[ugordan]

"Opposition surge" on Itokawa...
New update...

Update

One thing to note about the image on the right - the asteroid limb is very sharply defined and this could be a telltale sign that the original, much higher res image was greatly scaled down. I don't think it's the result of overexposure and CCD pixel "bleeding".
The science team really is teasing us, not releasing higher quality imagery yet!

[centsworth_II]

I'm encouraged by the fact that they went through with the "Opposition surge" experiment despite being down to one gyro. It must mean that there is little worry of lack of attitude adjustment fuel affecting landing and sampling activities.

[Bob Shaw]

I don't think it needs one big crater to erase all the others.  I think every impact digs a shallow crater in the existing rubble, and (a) shakes everything a bit, jostling rubble everywhere including on its own rim, and ( throws debris out at low speeds into loose looping trajectories that eventually reaccrete, further degrading any crater rims.

Ejecta fragments leave a surface at a range of speeds, fast at first in the impact process, then slower as energy diminishes during the process.  The faster stuff is just lost from an object like this, but the slower stuff can reaccrete.  Itokawa should eventually erode away, I suppose, but now we see it covered with the slow-moving and reaccreted ejecta.

The seismic shaking model is going to work a lot better with a solid (maybe fractured but still basically monolithic) asteroid such as Eros is believed to be, than with a true rubble pile.  A lot has been said about rubble piles in the past, but everything we've seen at high resolution has looked more like a monolith (surface expressions of linear fractures etc.)  Reported low densities on those bodies are probably due to open fractures rather than interstitial pore space in rubble.  Itokawa might be our first close look at an object consisting at least 50 percent of true rubble.

Well, that's my take on it up to now...

Phil

Phil:

The problem with impact ejecta on an object like this is that the escape velocity is trivial, so practically *all* initial ejecta should be lost, leading to an eroded surface. The obvious answer is that ejecta will re-impact the primary body after X orbits round the sun, and that an iterative 'de-energising' process will take place, within a general mass wasting environment. The interesting question - as this is all down to statistics - is what happens on objects with rotational axes aligned away from the plane of impacting debris? I suspect that the poles may therefore be the last gardened areas of the asteroid...

Bob Shaw

[RNeuhaus]

A new article about orbital evolution of the Itokawa asteroide that is erratic. Its orbit croses the Earth and Mar's orbits in a period of at least of over than several million years.

Next, we studied the orbital evolution of Itokawa about 100 million years in the future, and we found that the fate of Itokawa ends most probably by a collision with the sun or planets (Mercury, Venus, Earth, Mars). Only in a small probability, it collides to Jupiter, or it is thrown away farther than Saturn, or it is still alive orbiting in the near earth region. The probability of colliding with the earth is about once in one million years.

Don't worry with it for our epocus.

More information Click here

Rodolfo

[Phil Stooke]

The ejecta discussion here is going beyond what I can really claim to know enough about.

My position has been based on the idea that ejecta from an unconsolidated object (rubble pile) will have much less energy than ejecta from a monolithic rock. An analogy: fire a rifle at a boulder and a sand dune. The fragments from the boulder impact will fly faster than the bits thrown out of the dune. It's related to the force binding particles to the target, which must be overcome to free the particle.

In other words, I think most of the energy of the impactor is used up moving rubble around within the rubble pile, but not much in ejecting debris. Thus there is not much of a crater, and any ejecta is likely to be very slow-moving.

If anybody who understands energy exchange in an impact can enlighten me I would appreciate it. I don't pretend to be an expert in the impact process, but this is my understanding of the literature.

Phil

[maycm]

fire a rifle at a boulder and a sand dune.  The fragments from the boulder impact will fly faster than the bits thrown out of the dune.  It's related to the force binding particles to the target, which must be overcome to free the particle. 

In other words, I think most of the energy of the impactor is used up moving rubble around within the rubble pile, but not much in ejecting debris.  Thus there is not much of a crater, and any ejecta is likely to be very slow-moving. 

This leads to speculation about what will happen when the probe fires it's 'pellet' for sample collection.

I wonder if we will get anything dispersed for collection or will the thing just be absorbed into the rubble pile?

[Bob Shaw]

My position has been based on the idea that ejecta from an unconsolidated object (rubble pile) will have much less energy than ejecta from a monolithic rock.  An analogy: fire a rifle at a boulder and a sand dune.  The fragments from the boulder impact will fly faster than the bits thrown out of the dune.  It's related to the force binding particles to the target, which must be overcome to free the particle. 

Phil:

Interesting point! So we could be talking about an elastic vs inelastic collision scenario...

OK so far, I accept that the old 'rifle bullet into sand/rocks' argument would hold for relatively low-speed impacts where we don't see explosive effects, but things coming in fast might well be different (what a pity we never actually saw the Deep Impact crater!). All in all, I still think the poles could be the place to get a good sample...

Bob Shaw

[abalone]

Phil:

Interesting point!  So we could be talking about an elastic vs inelastic collision scenario...


Bob Shaw

I dont believe its so much a matter of elastic vs inelastic collision as both will be inelastic collision. In a rubble pile object the collision energy is dissipated by lots of secondary collisions and over much larger volume and average Ek will be smaller. It is therefore "less elastic" than for a solid object.

[Rakhir]

New article on Jaxa website (Which direction is "north" on Itokawa?) but no new image.
http://www.isas.jaxa.jp/e/snews/2005/1031.shtml

Distance from Itokawa : 5.1km
*Fourth day of the HP position keeping operation
*Functional tests on the touch-down operation were carried out.
*Observations on sampling site candidates were carried out.

Rakhir

[Phil Stooke]

Another update here...

http://www.jaxa.jp/press/2005/10/20051027_hayabusa_e.html

with a schedule of events during November.

Phil

[Guest_BruceMoomaw_*]

Looks like the entire sequence is "go" -- and to be completed on a pretty fast schedule. Now we'll see if they can pull it off.

[tedstryk]

Another update here...

http://www.jaxa.jp/press/2005/10/20051027_hayabusa_e.html

with a schedule of events during November.

Phil

Where does Minerva fit into this scheme?

[djellison]

I guess she'll be dropped off at the first sampling attempt?

Doug