Home Plate Speculations, Get it in now, before we know the truth! |
Home Plate Speculations, Get it in now, before we know the truth! |
Jan 25 2006, 04:10 PM
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#1
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
Down in the Front Page Stories board, Phillip asked what all of us UMSF types think Home Plate might be made of and how it was formed. He actually wants Jim Bell's speculations, but asked for UMSF's speculations, as well.
Since we're getting close to getting there, it's time for any of your uninformed speculations out there to be recorded for all posterity... I posted the following in that thread, but it really belongs here, so I'm reposting it here and inviting discussion. I figure that a lot of us don't bother to read the boards we don't stay actively involved with, so for all of you, this is new. Otherwise, I apologize for the repetitiion! Look at the vertically-exaggerated image posted here. Home Plate seems very obviously, in this stretched image, to be the remnant of an impact crater. There are several impact crater remnants in the inner basin, here. Each seems to have been formed in a surface that was a good many meters higher than the present surface -- those missing several meters have been deflated from this terrain, by some process, leaving the shocked "pedestal" remnants of the deeper cratering forms. Remember, when you make an impact crater, you don't just affect the surface. The disruption caused by the cratering event goes well under the surface, consisting of impact melt (if the impact is energetic enough) and shocked, brecciated rocks. The crater remnants we're seeing on the surface look like the brecciated and shocked rocks that were originally created in a bowl-shaped lining beneath this cluster of impact craters. I can see traces of at least five different craters within the inner basin, here. (The ridge of rock Spirit is passing right now is, in fact, a small crater remnant.) As for Home Plate, it sits within the largest and most well-defined of these crater remnants. Maybe such layers were exhumed in *all* of the craters here, and have since been completely eroded away -- but that doesn't seem right. We have traces of several craters, and in only one of them do we see any trace of this lighter-colored material. I'd have to think that either the impact target composition was different where the Home Plate impact occurred -- which seems a little unlikely when you consider some of these impacts are only a few tens of meters apart -- or that some other substance was deposited in Home Plate crater that wasn't deposited in the other craters. (Or that has been completely deflated from the other craters, if it ever existed there.) So, logic *seems* to point towards post-cratering material deposition accounting for the light-rock ring. Personally, I think it could have been water deposition. Home Plate could have been a puddle that was filled and dried thousands of times (maybe with an internal artesian spring) that resulted in aqueous transport and deposition. Or, it could have just been a good wind trap and it trapped a lot of light-colored dust. Hard to say. I'm not only interested in the light-rock ring's composition, I'm getting very curious about the erosion process that deflated the original surface. Could aeolian erosion have deflated *that* much surface, even over a few billion years? Do we need to postulate aqueous erosion, or even glacial erosion? Maybe the specific composition and erosion patterns we see on the light-rock ring will help us puzzle that out. -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Jan 26 2006, 05:38 AM
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#2
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Senior Member Group: Members Posts: 2228 Joined: 1-December 04 From: Marble Falls, Texas, USA Member No.: 116 |
I have to get in on this crapshoot. Although I have no idea what Home Plate actually is, as far as the rock type, minerals, or actual mode of origin, I do have some hypotheses based on what we have seen so far. It sure would help if someone would leak some spectral information that was likely collected with the mini-TES, or reflectance spectra based on the filtered imagery. (hint)
I think my first speculations on the nature of this area were mentioned here, and here. At this point, I still pretty much hold those views, though I suppose I could expand on them a bit, but it will be mostly be another way of describing what some others have already said. This whole valley seems to be filled with erosional remnants of layered rock units. Some appear as decent-looking mesas, and others are more degraded and less defined. I'm not sure that all of the "remnants" are the same unit as the Home Plate layers. I doubt they are, but they are probably pretty close, stratigraphically. I'll admit that I am not absolutely certain, but what little is left of the more resistant of the layers suggests to me a scenario where the original layers of fill were draped over a pre-existant topography. Alternatively, I can't rule out the possibility that some post-depositional, structural deformation has occurred. I think I see some slight concavity in HP. That could easily be from a draping effect, or the expression of an eroded syncline. While the rocks themselves may have originated from volcanic or impact events elsewhere, I don't see HP as the center of such events, only the place where the clasts settled, and were later eroded. Oh, and before I forget to ask again, will the person who originally proposed the name "Pitcher's Mound" for the curious mesa across from Home Plate please stand up and take a bow? That label has obviously become an icon that all here in the UMSF community have come to know and love. -------------------- ...Tom
I'm not a Space Fan, I'm a Space Exploration Enthusiast. |
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Jan 26 2006, 06:18 AM
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#3
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
QUOTE (CosmicRocker @ Jan 25 2006, 07:38 PM) Oh, and before I forget to ask again, will the person who originally proposed the name "Pitcher's Mound" for the curious mesa across from Home Plate please stand up and take a bow? That label has obviously become an icon that all here in the UMSF community have come to know and love. Sir, You will have to speak to the General, Sir! I believe this term originated at oh eight twenty six hundred hours on two zero September, 2005. Sir. The post was number one seven within the subject designated as "Stereo Home Plate!". -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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