Dawn Survey Orbit Phase, First orbital phase Options

[stevesliva]

stevesliva - Using the argument that other missions fall short, therefore it's just fine for Dawn to fall short isn't valid. They should all be stepping up to the plate and delivering as Phoenix did, and as VMC, Cassini and MER continue to do.

They're not falling short of what's ordinary, though. That was the point. When you ask them to do something that is extraordinary, you could at least do them the courtesy of admitting that it is. If the daily image release thing wasn't ordinary for HiRISE, for LROC, for MESSENGER, well then maybe I could understand the flogging here. It was, IMO, beginning to lack context. That's it. Not saying my heart's not in the same place.

Dear Dawn, thanks for the daily images. Some missions do more. Please follow their lead. The question of whether there can be too much released to the public was settled by pathfinder. There cannot be too much. It's be resettled by every mission that's turn on the firehose since.

[dshaffer]

IIRC, the question was whether all raw images will be made available as they were received (like MER), but was there a follow-up question as to why not?

I've read with interest the follow-on traffic, but it seems to me that the answer is no - the simple and direct question as to why this policy has been adopted for dawn image release, has not been asked/answered. We can all reasonably speculate that it has to do with budget or PI's wanting to publish or who knows what else - just curious as to whether anyone in the Project has stepped forward to explain the rationale for this decision.

[Mr Valiant]

Well, to change the tone of the conversation, I'm going to state what I'm looking forward to seeing,
namely - CAVES - or at least the observed openings. The presence or absence will tell us a lot about
Vesta's evolution and as early Mankind found out, caves are really useful things.

[dilo]

A stereogram from still frames 50&51 of the movie (thanks to Emily for this!):
(crossed eyes) (parallel)
A detail of sharpened snowman crates:

[pablogm1024]

Well, to change the tone of the conversation, I'm going to state what I'm looking forward to seeing,
namely - CAVES - or at least the observed openings. The presence or absence will tell us a lot about
Vesta's evolution and as early Mankind found out, caves are really useful things.

Talking about features, I think I would not step too much out of the line if I invite you to speculate about the feature in the red circle.

Sorry if the upload is in full size, someone please PM me to explain how to do the thumbnailing.

Attached thumbnail(s)

 

[Phil Stooke]

I think all the dark spots are caused by impact excavation of a buried dark layer. Most large craters reach under the dark layer and also excavate deeper bright material. This particular spot looks to me like a smaller crater that is almost completely within the dark layer, not reaching under it. If you enlarge it and brighten it it looks like a typical small crater with a lot of dark material on its inner rim and slumping down its walls.

Phil

[algorimancer]

The grooves/ridges are particularly interesting. Only one explanation makes sense to me, particularly after watching the rotation movie, and that is ring decay. Probably multiple impact-generated rings, at multiple orientations, over the course of Vesta's history. This is much as anticipated in the Small Body Grooves thread. We'll see more on Ceres

[ElkGroveDan]

My thought process is similar to Phil's. There exists darker material beneath the surface. The black streaks on the crater walls are caused by slumping and mass-wasting, possibly triggered or accelerated by regional impact shocks. The speckled area looks like it could have been caused by a spray of ejecta impacts. The other possibility is that a loose cluster of small debris impacted the region, perhaps a small Itokowa-like body was pulled apart in an encounter that set it on a trajectory toward Vesta.

[hendric]

I call geysers!

[MarkG]

Ring decay seems unlikely to explain most of the grooves, since many of them (especially the far-northern big ones) are not "great circles" and thus curve along the surface, and could not have underlain a ring system, even if the rotation axis had shifted. Better mapping of the Vesta surface and the gravity figure as the mission progresses will shed light on this. If the gravity field is "weird" enough, it would discourage ring formation.
When I look at the distribution of crater ejecta back onto a rapidly-rotating Vesta from the south pole impact (who did that simulation?), plus massive seismic forcing, and then extension cracking with debris collapse, I see a possible explanation. But extension cracking is a bit dirty, and doesn't usually result in such straight lines. So I am not satisfied yet with this picture.

[stevesliva]

When I look at the distribution of crater ejecta back onto a rapidly-rotating Vesta from the south pole impact (who did that simulation?)

http://www.planetary.org/blog/article/00002906

Jutzi/Asphaug... who incidentally just tried to explain the moon's farside/nearside dichotomy with impact sims.

[Gladstoner]

Could the layer of dark stuff (assuming that's what it is) be remnants of (the hypothesized) basalt flows that have been protected with a mantle of ejecta from the South Pole crater (SPC)? If so, subsequent impacts would serve to expose the basalt under the ejecta, as appears to be the case.

Speaking of SPC itself, what was used to determine an age of 1 billion years? Was it the lack of craters in its interior? In that case, 1 BY would be the age of a resurfacing of the interior, not necessarily of the impact itself. Considering that the the interior is a churned mess, any previous, readily observable cratering record would have been at least partially disrupted by the slumping and flow of material.

[Reed]

Speaking of SPC itself, what was used to determine an age of 1 billion years? Was it the lack of craters in its interior?

That estimate didn't come from Dawn data, so definitely not crater counts. AFAIK it comes from characteristics of the family of asteroids believed to have been produced by the impact.

[Gladstoner]

That estimate didn't come from Dawn data, so definitely not crater counts. AFAIK it comes from characteristics of the family of asteroids believed to have been produced by the impact.

Yeah. Now that I think of it, I barely remember reading something about that. I even have bits of one of those asteroids sitting on my desk.

[chuckclark]

With all this incredible photography, Vesta is going to be an excellent specimen for a foldable map.
Tayfun -- are you out there with your CADCAM machine still operable? How long until we have enough data (a "shape model" do they call it?) for you to carve one for me of this beast, er, lady?
Chuck