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Parlovero
2012-Sep-12, 10:31 PM
Hi,

I originally posted on Twitter about this (@therealjason), but here's a crop of a screenshot to give a better idea. I've highlighted the strange shapes that I saw last night while mapping. (Image attached)

Any idea what these are caused by?

Thanks! :-)

Jas

Parlovero
2012-Sep-13, 03:32 AM
Found a few more just now... :-)

17520

kmasterdo
2012-Sep-13, 05:43 AM
Hi Parlovero, did you try out the Deformation Features Glossary (http://cosmoquest.org/Glossary:_Deformation_Features) or (in general) the Surface Features Glossary (http://cosmoquest.org/Surface_Features_Glossary)? Just my first idea... (And by the way, welcome to the forum!)

Parlovero
2012-Sep-13, 02:14 PM
Hey there, thanks! I don't remember seeing a link to glossaries, but yes, these do help.

They appear to be wrinkle ridges, but maybe instead, wrinkle ditches? Am I seeing this wrong, or because of the shadows on the sides facing the sun (and the lack of shadow on the side in the opposite direction), they are lower in elevation than the surrounding area?

astrostu
2012-Sep-13, 06:05 PM
I would guess they're one of two things, can't really tell at the moment which. One would be boulder trails (boulders rolling around making grooves in the powdery surface), the other would be secondary crater chains, overlapping each other to a large extent. There are definitely some secondary craters in there, but I would lean more towards boulder trails.

Secondary craters are emplaced by ejecta thrown out of a primary crater when it's formed, and so it just lands and makes a crater. The fact that these appear to deviate around something makes me think it's more likely to be a boulder rolling and not wanting to roll up a hill. That's my guess for the moment, anyway.

kmasterdo
2012-Sep-13, 07:51 PM
Thank you for explaining this, astrostu!

Parlovero
2012-Sep-13, 10:59 PM
Thanks for the detailed explanation, astrostu! The boulder trails makes a lot of sense. :-)

So, another question: After reading about Dawn's science payload, I don't see anything specifically that can determine the depth of craters (like the height above Vesta's ellipsoid, maybe?). Is there a way that the Dawn team can determine crater depths, say, just using the Framing Camera and the direction of the sun? (grasping for straws here...)

astrostu
2012-Sep-15, 06:33 AM
I'm not on the Vesta team and not hugely familiar with their datasets, but I have seen some DTMs (digital terrain models), I think done with stereo pairs (http://en.wikipedia.org/wiki/Stereoscopy).

And, now that I dig a bit through my papers, Jaumann et al. came out with a paper in a special issue of Science this year, "Vesta's Shape and Morphology," where they state: "The survey mapping campaign was designed to obtain at least three different viewing geometries of Vesta, under similar illumination conditions, in order to construct a model of surface topography and to generate a base map by using stereo- photogrammetric analyses."

I don't see an obvious place where they say what the resolution is, but they do say that overall images were at a pixel scale of 260 and 700 m/px, so probably the horizontal resolution is no better than about 500 m to 1 km. From my experience with some Martian DTMs, the vertical resolution is usually pretty good, at the ~few meter level, maybe up to 25 meters uncertainty, but I'd need to read a more detailed paper than a Science one to get those kinds of details, and you'd probably need an independent method of determining topography to really know the error. But, uncertainties in exact pointing, lighting, and reconstructing the orbit will all contribute to those kinds of uncertainties.

To go back and look at this from a higher level, the short answer to your question is probably "yes, for big ones." If the pixel scale is about 1 km/px of the DTMs, my research (again with Martian data) indicates that they can probably get reasonable topography data for craters with diameters D ≥ 10 km.

As for your second question, yes, you can use photoclinometry (http://en.wikipedia.org/wiki/Photoclinometry) to get at some topography, but there are usually a lot more assumptions that go into it and I'm personally not a huge fan. But when that's the only thing you have, you gotta use it ;).

Kokahen
2012-Sep-22, 12:00 AM
Since the trails are multiple and not straight, they looks like formed by corrosion or some difference in material. Its only my guesses, ofc.

baskerbosse
2012-Sep-28, 12:42 PM
Hi Parlovero, did you try out the Deformation Features Glossary (http://cosmoquest.org/Glossary:_Deformation_Features) or (in general) the Surface Features Glossary (http://cosmoquest.org/Surface_Features_Glossary)? Just my first idea... (And by the way, welcome to the forum!)

Some of these features seem to match volcanic features.. For example the volcanic vent fissures picture looks similar to some patterns on Vesta. -Could these form from something else than Lava?

/Peter

astrostu
2012-Sep-28, 08:03 PM
To me, these really look more like "skipping" boulders/ejecta blocks rather than volcanoes. Coupled with the idea that the Vesta team (who have access to much more data than we do at the moment) say they don't see evidence of geologically recent volcanism, I think volcanic vents are much less likely.

baskerbosse
2012-Sep-29, 01:37 AM
To me, these really look more like "skipping" boulders/ejecta blocks rather than volcanoes. Coupled with the idea that the Vesta team (who have access to much more data than we do at the moment) say they don't see evidence of geologically recent volcanism, I think volcanic vents are much less likely.

Yes, lava seems very unlikely.
-However, what I was wondering, -could other liquids play the role of lava, creating similar features?
-For example water?

I have seen some strange tadpole shaped indentations that I'm having trouble visualising as rock bounces..
(Unfortunately, I can't seem to be able to bring any examples up right now..)

thanks,
Peter

astrostu
2012-Sep-29, 02:43 AM
Hard to get lava to look like water, the viscosities are way too different. On Earth, usually by a factor of 100-1000x, and even on the Moon, 10x. Also, there's the small issue of water not being at all stable on an airless surface in the sub-zero asteroid belt.

JohnD
2012-Sep-29, 09:50 PM
I would guess they're one of two things, can't really tell at the moment which. One would be boulder trails (boulders rolling around making grooves in the powdery surface), the other would be secondary crater chains, overlapping each other to a large extent. There are definitely some secondary craters in there, but I would lean more towards boulder trails.

stu,
Well spotted parlovero!
We had this "rolling rocks" exoplaination suggested for the 'grooves' on Phobos.
But surface gravity on Vesta is 0.025 of g (Phobos 0.009g at best) Will that let rocks roll from an impact, rather than fly off to a secondary impact near or far?
Even on Earth, a rock rolling down a slope soon gains enough speed to start to hop and bounce, and one dislodged by an impact will start off with a high velocity.

There are similar formations on the edges of the image, at twelve and ten o'clock, looking like rilles, possibly with origins similar to Lunar rilles. There is another to the right of the chains at approx, two o'clock from the lowest marked formation. All these formations could have come later and joined adjacent craters in the chain, or could have preceded and been accentuated by the chain event.

John

JohnD
2012-Sep-29, 09:55 PM
See here

baskerbosse
2012-Sep-30, 06:29 AM
See here

That looks a lot like the patterns you get in new snow underneath a tree, as snow falls from branches..

baskerbosse
2012-Sep-30, 07:09 AM
If you have a track of a rock rolling along the surface, shouldn't there be a rock at one end of that track?

astrostu
2012-Oct-02, 07:49 PM
This makes me think that we're talking less random rolling rocks and more likely ejected material. That way it will have enough momentum to roll uphill, or even just make these long chains of craters. I'm still thinking that volcanic is a less likely explanation for this.

JohnD
2012-Oct-08, 09:50 AM
Well, well! A bit of Googling found me this:
http://www.telegraph.co.uk/science/space/9080580/Rolling-moon-boulder-photographed-by-Nasa.html
On the Moon, the track of a rolling rock, complete with rock at the end of it!
Clearly it rolled and bounced in Moon gravity, 0.17g. The size and spacing shows how it slowed before stopping.

Compare with the Vesta pics.
No rocks at groove end.
Lower resolution can merge a crater chain into a groove, but wouldn't you expect some indication that the roller slowed before stopping?
And to explain these curved tracks would require a complex contour, that directed the boulder one way then the other. No doubt there are complex contours on Vesta, but producing such regular tracks?

Could ejected material causing secondary cratering include 'rods' of material? I'm thinking something like 'chain shot' from 18th Century naval warfare, two cannon balls connected by a chain, used to destroy rigging. Could the ejecta be so semi-solid as to produce a similar projectile?
John

astrostu
2012-Oct-08, 06:18 PM
Secondary craters can show a huge range of morphologies (the way they look). They can look like any normal crater, they can appear in chains (including broken-looking angular chains that aren't 100% radial from/to the primary), clusters, long troughs, etc. Big pain. I provided some examples in this paper (http://about.sjrdesign.net/files/papers/2011_RobbinsAndHynek_JGRP_Secondaries.pdf) - check out the figures 2, 4, 5, and 6 and you can see a sampling of the morphologies on Mars.

I'm not saying these are definitely one or the other, or either ... but at this point I think they're most consistent probably with low-velocity secondary crater chains. Though now that I look more closely, check out the 1:30 position relative to the blue circle, about 1 circle radius away. I see what could be a boulder sitting at the end of that chain.

JohnD
2012-Oct-11, 02:54 PM
I'd like to read your paper Stu, but it doesn't download.
Is the link intact?
John

astrostu
2012-Oct-11, 05:17 PM
I'd like to read your paper Stu, but it doesn't download.
Is the link intact?
John

Should be, works for me.

kmasterdo
2012-Oct-11, 07:22 PM
I'd like to read your paper Stu, but it doesn't download.
Is the link intact?
John

For me, the link works, too. It just takes some time to download for me.

astrostu
2012-Oct-11, 10:28 PM
Yeah, the paper's about 11 MB, so it could take a while.

JohnD
2012-Oct-30, 11:25 PM
Thanks, stu, if left for a while, it loads!
I see your point, and I see your 'boulder'. I assume that the emblem on the right margin shows the sun's direction, sothatthe highlight to the right of the dark patch could be boulder and shadow. Bit there is also a highlight around the left of the 'shadow'; could this be a pit crater?

John

astrostu
2012-Nov-03, 08:57 PM
Could you annotate the image to show what you mean? I don't see any pit craters nor central pit craters in the image. And yes, the half-sun on the right side is meant to indicate the direction from which the sun comes.