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Unmanned Spaceflight.com > Other Missions > Cometary and Asteroid Missions > Dawn
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Paolo
I think it's time we start a new thread
dilo
Good idea, Paolo!
Dawn's ion engine have been OFF in the last hours (at least 9 hours from my checks) and, as expected, now spacecraft started to accelerate:
Click to view attachmentClick to view attachment
at current distance, I espect an acceleration toward Vesta of 1,0e-4 m/s2; considering current phase angle, close to 90, this should cause an increase of total velocity close to 1 mph each 2 hours... until next engines power on!
pablogm1024
Would it be worth renaming the topic to Survey Orbit Phase, given that it is the name that the mission ops team uses for the first orbital phase?
Bjorn Jonsson
QUOTE (pablogm1024 @ Jul 17 2011, 02:28 PM) *
Would it be worth renaming the topic to Survey Orbit Phase, given that it is the name that the mission ops team uses for the first orbital phase?

Done - and congratulations to the Dawn team!
dilo
This is an answer to Greg question (from the old thread):
Your question wasn't so silly because helped me to find many answers! wink.gif
You had a nice idea about plotting escape velocity (which depends on distance from Vesta) toghether with speed... this my updated distance/speed plot, zoomed on last weeks:
Click to view attachment
You can clearly see the "capture event", when red curve goes below yellow one (speed axis on the right).
Well, as told in the press release nobody knows the exact moment of such event because Vesta mass is only roughly known for the moment (I used 2.69e20Kg value, reported also in Wikypedia; uncertain should be around 2%, which means 1% uncertain in escape velocity).

EDIT: meanwhile, Dawn is using again propulsion and speed seems stabilized now...
dilo
With engines on, Dawn still decelerating, even though at a very slow rate (only 1m/s in last 20 hours) due to Vesta gravity... this is an update of previous plot with a new one (always suggested by Greg) showing speed as a function of distance from Vesta instead of time; I also added a curve showing speed required for circular orbit (pay attention, this is true only if velocity vector is perpendicular to distance vector and this is not the case of Dawn, at this moment!):
elakdawalla
OK this is making me absolutely crazy. Another image release (yay!) but as with all the previous image releases the reported scale is wrong. They keep reporting the pixel scale for the original, unenlarged image, and then they post an image that has been enlarged (badly) by some non-integer factor and fail to divide the pixel scale by whatever their enlargement factor was.
Stu
Hands up, I don't understand all the tech stuff, but I sense your frustration Emily. sad.gif

Pretty cool view, tho... more and more Mirandan...

Click to view attachment
Phil Stooke
Another version of this beautiful new picture.

Phil

Click to view attachment
bagelverse
Wow, stunning image.

While the south polar peak is either impact derived or tectonic, it certainly
reminds me of Ayers rock in central Australia. Nice hard hard of
rock that says "I am not going anywhere, no matter what you throw at me".

Also the ripples around the south polar peak really look like ripples in a pond
or maybe just wrinkles from shinkage.
Stu
Thanks for posting those links. Used the tiff file to creare a cleaner view...

http://twitpic.com/5s9axu
Juramike
That's really nice, Stu!
volcanopele
I think I shrunk the original image to something approaching the original resolution. I've also applied a light unsharp mask here:
punkboi
Congrats to the Dawn team for a successful orbit insertion! Now looking forward to a color image of Vesta... smile.gif
belleraphon1

Thanks DAWN team for releasing these.

A lot to look forward to in the coming 12 months!

Mirandian indeed.

Craig
Drkskywxlt
Is that picture facing the south pole?

For somewhat not geologically-minded, what is reminding all of you about Miranda? I don't see the similarities really...
ugordan
A faux-color version based on color derived from Hubble WFPC2 F673N and F439W filters:

Click to view attachment
belleraphon1
Drkskywxlt:

Call it exhuberance.

Mirandian was perhaps more prominant in the lower resolution view from July 9th. Go to NASA photojournal and explore
Miranda.

Miranda has what I would call sectional terrain (not a geologist either nor do I pretend to be). Odd blocks of internal resurfacing surrounded by cratered terrain.
As we get closer the comparisons do seem to break down a bit. Is this a demonstration of how small bodies go through an early stage of internal processing?

But is it not wild that we can even make subjective comparisons of bodies so far apart in space and time!
That is what some 50 years of solar system exploration has given us.

Glad I was born to see it from the start.

Craig
kap
QUOTE (ugordan @ Jul 18 2011, 03:09 PM) *
A faux-color version based on color derived from Hubble WFPC2 F673N and F439W filters:
]


Nice work. What does everyone think of that big scarp on the upper right area of the image. Could that be the edge of the southern hemisphere impact crater?

-kap
Juramike
QUOTE (kap @ Jul 18 2011, 06:54 PM) *
What does everyone think of that big scarp on the upper right area of the image.


That's a neat cuspate scarp, and another just beside it. I'm looking at the small wavy pile of stuff right in front and wondering if material slumped to reveal an abrupt scarp.
MarkG
Boys and girls, it's "Rampant Speculation Time...."
The patterns on the South Pole crater floor do resemble both Miranda, and Earthly sea-floor spreading. Perhaps a shock-melted mantle zone convected for a while, rafting surface debris and local volcanics into linear rows from spreading crack centers. Fun to speculate.
Vesta had it's "bell rung" pretty good with the impact, maybe there was a surface wave interference pattern that distributed things in the pattern seen.
Relaxation after impact, with the core wanting to re-center, and perhaps migration of the rotation axis, could cause some of the features we see. Also the floor striations could be caused by compressional wrinkling from this relaxation, plus landslides and collapse blocks from the crater rim.
Is the central mountain a volcano, an intrusive diapir, an infall debris pile, a garden-variety crater central mound, or a combination?
Stay tuned!

belleraphon1
"But is it not wild that we can even make subjective comparisons of bodies so far apart in space and time!"

My quote from my last post here.

Miranda and Vesta...far away in space but perhaps not in time. The period of resurfacing may have been in the same period of time. Early in solar system history.
Once again are we seeing how smaller bodies go through an early period of furious internal resurfacing that is restricted to segregated internal blocks of activity.
A herterageneous stew that cooks in spots but stays stone cold in others.

Shaken... not stirred?

Craig
MarkG
There is a big difference between Miranda and Vesta, however. The difference is the presence of ice and tidal forces on Miranda, both largely absent on Vesta.
Ice is quite ductile, and small gravity can cause it to flow, but plain rock, like on Vesta, don't flow unless it is pretty much hot enough to melt, and the interior pressures in Vesta, with it's light gravity, are not going to contribute that strongly.
One of the big questions is how warm was the interior of Vesta at impact? We already know (pretty much) that Vesta got hot enough early to differentiate its core/mantle/crust, and then we can ask how much of this heat was left at impact. Since the planet as a whole did not re-spherize itself, it must have been largely cooled to a solid at impact time. Perhaps some of the core was still liquid -- radioactive decay might have kept it going a while.
On the other hand, Quite some time might have passed since the planetary system formed and cleared out the nebula and most debris before the impact. We know that a significant amount of asteroidal objects are dynamically related to Vesta and are shards of the great impact. The surface of Vesta also does not appear to be crater-saturated. (With further imaging, crater counts should be able to give a rough age estimate -- looking forward to that.)
So it seems (arms waving wildly) that the energy for reshaping parts of Vesta had to be delivered by the energy of impact. How much shock melting could accomplish is unclear, and a better answer is in the hands of the planetary modelers and the mega-computers.
An interesting idea is the possibility that accumulated surface volatiles were stirred up by the impact and ablated by solar and impact heating, and Vesta was a giant comet for a while...
Well, I think I've embarrassed myself enough for now. Its a free country, gotta love it.
Steve G
Sometimes it's easier just to rotate and crop, and just look at a single feature at its best orientation. I just love these cliffs!
nprev
I think we'll definitely need a true global view before we'll be able to understand what we're seeing now, but my working hypothesis is that Vesta was damn near remelted globally after this tremendous impact. However, it probably cooled quite quickly as well; we may well be seeing a landscape frozen in time after a catastrophe, perhaps like the ancient Earth (sans atmosphere & oceans) after the big whack that formed the Moon.
Explorer1
How far will coverage of the northern hemisphere go; will it stay mostly in shadow for the full duration of Dawn's visit?
belleraphon1
Shaken or stirred?

That is the question.
Gladstoner
On second thought (or third), it looks like material from the original crater 'wall' has slumped toward the center -- basically the same as what occurs in craters on the moon and Mercury. In this case, though, the slumps have slid all the way to the central peak/uplift, and continued to flow as they were displaced by more material sliding down from above. After eons, a jumbled flow was the result.
MarkG
Replies...
My understanding is that the North pole of Vesta will just begin to be illuminated at the end of the Vesta mission, so there will be eventual global photo coverage by Dawn.
Also, mass wasting from the crater sides does not seem to explain the 5-km-ish spaced parallel ridges on the crater floor. I'm wondering if they are ridges of olivine....
tasp
Love the "asteroid size comparison poster", amazing to see all the suspects in a police lineup style poster, and LOL, I gets my 1 pixel Itakowa comparison!
antipode
I can't wait to see...errrr...the antipode of that crater! Mega chaotic terrain?

P
Gladstoner
QUOTE (MarkG @ Jul 18 2011, 11:02 PM) *
Also, mass wasting from the crater sides does not seem to explain the 5-km-ish spaced parallel ridges on the crater floor. I'm wondering if they are ridges of olivine....


They could be pressure ridges between adjacent debris flows.
Gladstoner
A little bit of Vesta on Mars?:

Click to view attachment

And on Earth?:

Click to view attachment

(Double Spring landslide complex, Oregon)

I had a heck of a time finding a decent example of a terrestrial landslide to compare to Vesta. If the grooved terrain is indeed a system of debris flows, they may turn out to be the finest example of the process anywhere in the Solar System.
centsworth_II
I was intrigued by the quick look Cassini got at the conical craters of Saturn's Phoebe. Now it looks like we'll get a much better look at the same sort of crater on Vesta. The images below are very roughly to the same scale. Although Vesta is a little more than twice the diameter of phoebe, the craters in question seem to be about the same size on both bodies.
Click to view attachment
centsworth_II
QUOTE (Drkskywxlt @ Jul 18 2011, 05:59 PM) *
For somewhat not geologically-minded, what is reminding all of you about Miranda? I don't see the similarities really...

From The Planetary Society Blog:
"The interior of that south polar basin sure looks weird. All around the central peak are chevron-shaped ridgy features that bring to mind Miranda -- which, by the way, is very similar in size to Vesta."
Drkskywxlt
QUOTE (centsworth_II @ Jul 19 2011, 07:35 AM) *
From The Planetary Society Blog:
"The interior of that south polar basin sure looks weird. All around the central peak are chevron-shaped ridgy features that bring to mind Miranda -- which, by the way, is very similar in size to Vesta."


Yeah...I guess I can see that. To me (again, not a geologist), it just all looks like grooves similar to those on other small bodies like Phobos and Lutetia.
Stefan
QUOTE (elakdawalla @ Jul 18 2011, 09:21 PM) *
OK this is making me absolutely crazy. Another image release (yay!) but as with all the previous image releases the reported scale is wrong. They keep reporting the pixel scale for the original, unenlarged image, and then they post an image that has been enlarged (badly) by some non-integer factor and fail to divide the pixel scale by whatever their enlargement factor was.


The last few images were enlarged by an integer factor. Did you find something wrong with how they were enlarged?

While the quoted pixel scale is indeed not valid for the enlarged image, it is the relevant number for knowing the smallest detail that can be resolved.
centsworth_II
QUOTE (Drkskywxlt @ Jul 19 2011, 07:37 AM) *
...it just all looks like grooves...
All groves are not alike. There are straight grooves, sinuous groves, grooves with right angles.
Stefan
QUOTE (punkboi @ Jul 19 2011, 12:14 AM) *
Congrats to the Dawn team for a successful orbit insertion! Now looking forward to a color image of Vesta... smile.gif


There is a false color image on the MPS Dawn page (click the latest headline).
MahFL
The focus is getting better.
The Clangers definetly live there.
Steve G
The south polar crater is, by appearances, a flat slice right across the south pole. However, gravity is always pulling towards the center of the body. So on the outer limits of this flat massive basin, it is gravitationally speaking, an up hill slope. This would naturally draw the loose surface material towards the center of the crater, and perhaps create the cracks and rifts, would it not?
algorimancer
Was arrival facing the south polar crater planned, or a coincidence of orbital mechanics and intent to enter a polar orbit? I understand that it is a target of interest, just wondering about the extent of the planning process in that regard.
Juramike
Coordinated views of the normal and contrast-enhanced IR composite of 4 Vesta
(lineup is approximate) note the 4-pack of craters to the N in both images.

Click to view attachment
Phil Stooke
Nice one, Mike.

The orange spot in the false color view coincides with the darker spot seen in distant views, including the 'crater with tails' as someone described it, on the edge of the smooth patch we saw a while ago.

Phil
Phil Stooke
Here's a composite to illustrate that.

Phil

Click to view attachment
elakdawalla
QUOTE (Stefan @ Jul 19 2011, 05:22 AM) *
The last few images were enlarged by an integer factor. Did you find something wrong with how they were enlarged?

The most recent one wasn't -- its enlargement factor was something around 2.2. And the resolutions stated (and widely requoted) in all the released captions are just wrong.

With spherical bodies it is very easy to back out an accurate image resolution from a global image -- measure any diameter and you're done. But for bodies with very different principal axis lengths, especially irregular ones like Vesta, it's hard to do this accurately, which prevents me from doing size comparisons. Size comparison posts are some of the most popular things that I do, which is why this is driving me so crazy.

As of yesterday I think the press person at JPL now understands what I am complaining about, so hopefully we'll see captions fixed soon. Of course what I really want is for them to quit enlarging the released images.
MarkG
QUOTE (Phil Stooke @ Jul 19 2011, 08:11 AM) *
Nice one, Mike.

The orange spot in the false color view coincides with the darker spot seen in distant views, including the 'crater with tails' as someone described it, on the edge of the smooth patch we saw a while ago.

Phil


The orange area is around the sub-solar point, so I think it just represents daytime heating. Over time, a strong lead or lag behind nearby features with different times-of-day (Vesta Sols!) would be very interesting.
Stefan
QUOTE (elakdawalla @ Jul 19 2011, 06:51 PM) *
The most recent one wasn't -- its enlargement factor was something around 2.2. And the resolutions stated (and widely requoted) in all the released captions are just wrong.


This image was enlarged by a factor 2 (I know because I enlarged it). The resolution of the image as shown here is actually close to the quoted value. But what do you think of the caption here? The media will take that image and do with it whatever they like, and then quote the original numbers.

Yes, I understand your concern about the caption, and no, I didn't write it.
elakdawalla
You did the enlargement? It's great to actually talk to someone who knows what's going on smile.gif So tell me where I'm wrong here. The diameter of Vesta in that released image is 860 pixels. At 700 m/pixel (1.4 / 2x enlargement) that gives you 600 km diameter, which I *think* is much too large.

If the pixel scale were rounded incorrectly and the original image scale were 1.3 km/pixel then it would correspond to 560 km diameter, which is within the accepted range of Vestian diameters...

You're right that reporting pixel scales will inevitably result in mainstream media screwing things up. For that reason I'd actually advocate abandoning pixel scales -- ONLY IF the images get released at their original resolution, or if they are enlarged by whole-number factors that are stated in released captions. Those of us who care about these things will get the numbers right.
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