Mercury Flyby 1 Options

[elakdawalla]

Any comments with respect of the origin of rays?

The rays really, really, really look like extensional features, little graben, radiating out from some upwarp at the center of the crater. After staring at the image for a while I am leaning toward the interpretation that the crater and the fractures have nothing to do with each other, that the crater simply happened to form on top of the approximate center of the preexisting fractures. The other possibility is that the fractures show you lines of preexisting weakness in the crust in the center of Caloris basin, so that when the impactor hit it triggered the deformation at the surface. Regardless of which idea you subscribe to, though, the general plan and structure of the fractures results from preexisting structures in Caloris and the position of the crater on top of them is coincidental.

--Emily

[pgrindrod]

the 'spider' feature looks quite a lot like some kind of giant radiating dike swarm. the troughs (graben) form above the subsurface dikes, which radiate from some central magma chamber. there are some on earth, probably hundreds on venus (which i’ve done a bit of work on), and possibly some on mars too (alba patera for example).

it’s a shame that in this case, the central part of the radial fracture pattern is obscured by that impact crater. what are the chances eh? i agree emily, the crater position looks coincidental to me.

pete

[tedstryk]

This is probably just superficial, but it really looks like what sometimes happen when you throw a rock onto a frozen ice surface that hasn't fully frozen underneath but is frozen enough that the rock doesn't break through to the water. Perhaps it happened while their was still liquid magma under the hardened surface of Caloris.

[DFortes]

I don't know if anyone else has mentioned it, but the spidery thing looks similar to features on Enceladus, where impact craters appear to have modified the stress field in the crust so as to 'focus' fracture sets.
Anyway, that's my tuppence-worth.

[Julius]

This is probably just superficial, but it really looks like what sometimes happen when you throw a rock onto a frozen ice surface that hasn't fully frozen underneath but is frozen enough that the rock doesn't break through to the water. Perhaps it happened while their was still liquid magma under the hardened surface of Caloris.

I believe laser altimeter data will help shed further light onto the nature of the' spider'.

[vikingmars]

Here are the results of my own Messenger imaging color processings : a lot of science to be expected from this wonderful mission !
Enjoy

Attached thumbnail(s)

 

[JJR2]

After all the whining I did earlier, I'm just now watching recordings of the MESSENGER press conference (I may have missed parts of the forum disscussion, too---I apologize in advance).
Looking at the Caloris "spider" feature, ( http://messenger.jhuapl.edu/gallery/scienc.../Prockter06.jpg ) it looks like some of the surrounding small craters are concentrated into radial lanes, especially in the upper left quadrant of the image. Why would impact ejecta, if that's what did this, do that?
Next, to grossly oversimplify: assuming Mercury has a large, active, at least partly molten core, and considering the Solar tidal forces acting on it, and so on, why does the apparent volcanism here seem to more closely resemble the Moon than, say, Io?

[JRehling]

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[belleraphon1]

All... love the visuals..... and I think the "spider" will be just one of many surface suprises...... and those color mosaic... what splendor.....

What really strikes me is the magnetic field. Only three solid planetary bodies in Sol harbor intrinsic magnetic fields. Mercury, Ganymede, and Earth. Current theory holds that intrinsic magnetic fields require rotating liquid iron cores. Which implies hot interiors that have not cooled down. Two of these worlds, Mercury and Ganymede, almost the same size, but of VERY different surface composition (rocky versus icy), have scarred, rifted, older exteriors. Worlds that are young at heart..... but old on the outside (kinda like ME).

And the vageries of the exospheric atmosphere...... worlds are so much more than what we can sense, visually.
I really want to dive under that silicate skin and rove the liquid waves of iron..... what are your secrets? why are you there?

Craig

[nprev]

Poetic, Craig; well said!

Don't forget also that Mars used to have one, and it quit (why?) Messenger's study of Mercury's magnetic field may well be the most enlightening part of the entire mission in terms of comparative planetology.

EDIT: I just discovered that our resident Poet Laureate has had a second poem about the first encounter published by the Messenger team: http://messenger.jhuapl.edu:80/poem2.html

I never cease to be amazed by both the range and depth of talent & knowledge displayed by UMSF members. Enjoy!

[belleraphon1]

Thanks nprev!

But Stu is the true jewel..... beautiful, sir!

Yes, it appears Mars had an intrinsic magnetic field early on..... and some of the remnant frgaments are fairly strong!

As for Venus... hmmmmm..... the lack of a field cannot be soley due to slow planetary rotation, Mercury's rotation is long as well..... Venus I would also love to dive into...... does she have one thick lithosperic plate over a stagnant mantle and core?
Or are there other complications................ ???

All just so fascinating..... I was born when planets were basically just dots in the sky, litttle known.... and now I can virtually partipate in roving worlds....

Craig

[Gladstoner]

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[Juramike]

The spider grabens seem to radiate from a dark albedo feature that is offset from the crater.

Nice illustration and observation!

[Phil Stooke]

The spider fracture pattern looks to me like what I would expect from a dome-like uplift - either related to isostatic compensation in the old basin, or later intrusions.

But I'm particularly interested in this feature on the SW edge of Caloris:



a diffuse halo nothing like crater rays or ejecta. The multispectral images show it has a non-impact-like composition, as well. And it has an irregular depression in the middle. To me, it looks like a volcanic plume deposit of some kind.

Phil

[nprev]

Nice find, Phil! That is indeed intriguing. Additionally, the thing looks like it's sitting on some sort of darker flow itself, or at least there seems to be a sharp boundary (a scarp?) to the right of the feature.

Can't wait for the orbital phase...bet we find a lot of things like this!