Dawn Survey Orbit Phase, First orbital phase Options

[Explorer1]

Our first good look at the northern hemisphere, if I'm interpreting it right. Very ancient looking.

[jasedm]

Visually very similar - Phoebe v Vesta

Attached thumbnail(s)

 

[Juramike]

False-color coordinated image released by the Dawn spacecraft team today as PIA14680.

[Juramike]

So...shallow fresh craters make visually bright (false-color yellow) stuff (iron-rich material), will deep craters dredge up dark (false-color orange) iron-poor material.

What is the really-dark false-color blue stuff? Melted iron-poor stuff in cracks and fractures or iron-poor poofy dust?

[Phil Stooke]

Poofy dust? (not that there's anything wrong with that)

Phil

[Gladstoner]

Is the dark, blue-purple color due to some spectral signature, or is it the effect that a darkish to nearly black material has on the false-color scheme?

Or both?

Or something else altogether?

FWIW, 'poofy dust' has my vote.

[Juramike]

It is definitely darker in the "normal" grayscale image (clear filtered image? centered at wavelength...?) So it is low albedo.

From the description of the false color image since it is "brightest" in blue wavelengths, it means that:
the ratio of 750 nm to 450 nm is v. low (dark in red channel of the false color image)
the ratio of 950 nm to 750 nm is v. low (dark in green channel of false color image thus iron poor (iron absorbance at 1000 nm)
the ratio of 450 nm to 750 nm is relatively highest, (brighter in blue channel of the false color image)

So it is a "dark blue rock", or at least not as much visible red as the other rocks. No clue by how much the ratio is. The rock might appear only dark bluish even if you totally jacked up the saturation of a normal photograph.

'Course this could also be a grain size effect. I'm trying to remember if smaller grains are generally bluer or redder given the same composition. Help?

[ugordan]

Well, this is just lovely...

[john_s]

'Course this could also be a grain size effect. I'm trying to remember if smaller grains are generally bluer or redder given the same composition. Help?

Small grains of reddish materials (i.e. most rocks) should be less red than larger grains, because the smaller particles scatter more and absorb less. The reverse is true for bluish materials such as water ice- smaller grains (snow) look less blue than larger grains (big chunks of ice).

John

[elakdawalla]

This latest image of the south polar central mound is really cool-looking but I just don't know what to make of all of the different ridgy textures at all different scales. Any geologists out there want to try some arm-waving?

[ugordan]

That kind of reminds me of Rhea's splat crater from up close.

[elakdawalla]

I don't know if I agree. That texture outside the Rhea splat crater is pretty reminiscent of chevron-like patterns in ejecta that you see in lunar craters too. This is decidedly different. The parallel ridge sets definitely seem tectonic. But there'll be a few parallel ridges in one place, then some in another place with a different orientation and spacing, and some places where things cross.

[JohnVV]

Well, this is just lovely...

18 to 24 months ....

Someone with "first use" must be waiting for a grant to come through ????
If not then what ?

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but I just don't know what to make of all of the different ridgy textures at all different scales. Any geologists out there want to try some arm-waving?

dose GEOlogy even apply to a lose collection of gravel

The parallel ridge sets definitely seem tectonic

they look more like what one sees when hitting or pushing a damp sand castle at the beach

or better yet
forking a peanutbutter cookie - with macadamia nuts

a sticky loose conglomerate

[Phil Stooke]

I'd say lots of normal faulting as the surface adjusts to a significant change in shape, post-impact.

"does GEOlogy even apply to a loose collection of gravel"

Sure does! Geologists frequently work with unconsolidated materials.

Phil

[Gladstoner]

My arm-waving interpretation of the surface within the South Pole Basin :

[attachment=25375:Vesta_so...volution.PNG]

Here, sections of the rim slump down and crumple as they slide against and around the central mound. More slumps slide down and deform the existing deposits. After awhile, there is a (*subtly*) Enceladus-like jumbled mess.

The slumping process was relatively fast at first, but slower creeping of material would have continued to deform the surface over time.

I'm not sure about the parallel features on the central mound. Perhaps the debris flows placed some stress on the edifice as they piled up.

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This corkscrew-like feature here:

[attachment=25376:Vesta_sausage.JPG]

reminds me of the 'sausage factory' on Enceladus:

[attachment=25377:Enceladus_sausage.jpg]

It looks as if the surface here was stressed in one direction and then 'rolled' in another.