Home Plate Speculations, Get it in now, before we know the truth! Options

[Shaka]

AND they wear sweaters while they play it!

[stevesliva]

This is off topic, but I couldn't help but notice that this topic has thrown the "Ads by Google" a real curve ball. 

I went to look, but I've got Adblock... I highly recommend it.

[dvandorn]

What's 'baseball'?

Is it like... ...Rounders?

Yes. But it is, in absolutely NO conceivable manner, ANYTHING like Cricket!

-the other Doug

[djellison]

I went to look, but I've got Adblock... I highly recommend it.

There's no need to specifically for this place. As I mentioned when introducing the google ads - they are fundamentally optional. If you check the bottom left of the forum, you can pick a skin to have ads, no ads, or a search box.

Doug

[CosmicRocker]

OT, again. Personally, I'm happy to see the ads here. They are very unintrusive, and I click on them from time to time, to support this amazing forum in another small way. Gee, you've really got to look for them. It's not like they're in your face.

Of course, people are free to do what they want, but I'd encourage folks to not use the sans-ads skin. Where else can one go to have access to such fine discussions on space exploration, the ability to submit questions to the stars of space exploration, and a host who can apparently request the reprocessing of pancam sequences.

Support UMSF. BTW, have you visited the shop recently? I've been looking at that clock for my next purchase, but it would be nice to have a few more items to choose from.

[Guest_paulanderson_*]

Today's MER update makes interesting references to the "frothy" rocks (using their term) Spirit has been seeing as it nears Home Plate.

http://marsrovers.jpl.nasa.gov/gallery/pre.../20060127a.html

"Spirit first encountered basalts at its landing site two years ago, on a vast plain covered with solidified lava that appeared to have flowed across Gusev Crater. Later, basaltic rocks became rare as Spirit climbed Husband Hill. The basaltic rocks that Spirit is now seeing are interesting because they exhibit many small holes or vesicles, similar to some kinds of volcanic rocks on Earth. Vesicular rocks form when gas bubbles are trapped in lava flows and the rock solidifies around the bubbles. When the gas escapes, it leaves holes in the rock. The quantity of gas bubbles in rocks on Husband Hill varies considerably; some rocks have none and some, such as several here at FuYi, are downright frothy."

In particular:

"The change in textures and the location of the basalts may be signs that Spirit is driving along the edge of a lava flow. This lava may be the same as the basalt blanketing the plains of Spirit's landing site, or it may be different. The large size and frothy nature of the boulders around Lorre Ridge might indicate that eruptions once took place at the edge of the lava flow, where the lava interacted with the rocks of the basin floor. Scientists hope to learn more as Spirit continues to investigate these rocks."

Could this possibly indicate Home Plate being some kind of volcanic remnant as some had suggested? It would be cool if the possible remaining crater rim (Mitcheltree Ridge) partially surrounding Home Plate turned out to be an eroded old caldera instead... regardless of what it actually is, I think it will be very interesting, and we're getting pretty close now.

[nprev]

Hmm...If HP is indeed a volcanic structure, I wonder if the salt deposits and other 'volatile-enriched' sites are hydrothermal rather than evaporative artifacts. In fact, some of these rocks almost seem as if they might have been immersed in hot water at some point; I've seen etched, spongy red sulfurous rocks around natural hot springs in Montana before.

[CosmicRocker]

Whoah! That was an interesting press release, Paul. Thanks for the alert. I know better than to speculate too much about such things as my bedtime approaches, but that is definitely interesting news. I wasn't expecting to see the basin basalt lapping up into this area, but maybe the "froth on the broth" did. If you had a large glass of beer (or a small one, for that matter), the bubbles would rise to the top, would they not?

[edstrick]

I find Silylene's ideas presented several postings back quite plausible. I've tended to think that the feature is a crater-bottom deposit in a crater that is now largely eroded away -- hardly a new idea here. However, it is not necessarily a salt deposit, though it may well be salt rich. From orbital geologic studies, Mars has a long history of being mantled with thin to thick eolian deposits and then the deposits being stripped away, leaving essentially unaltered surfaces.

My speculation has been that HomePlate is the remnant of a deposit on a crater floor that was cemented enough that it's been resistant to erosion. You could have atmospheric dust... silt to clay-sized particles, that was eroded from some regional deposit that was salts-enriched... maybe 10-20% salts. Perhaps after a major flood event, you get transient salt-flats over large areas that then tend to get stripped and redistributed and finally remixed back into the global dust-inventory.

Anyway, the Columbia hills, though they contain solid, coherent rock layers and units, seem in some way jumbled, maybe much of them are debris deposits like ejecta blankets. Unlike on the moon, where the absence of water water lets hot ejecta blankets (like the highland megaregolith and impact basin ejecta) sinter and re-weld into reasonably hard rock, the presence of water in the martian crust will make ejecta blankets icy, to wet or at least damp, to steamy. Not easy to weld back into hardrock. The presumed crater that held homeplate may have punched through a thin layer of basalt (the dark rubble) into generally poorly consolidated materials of the Columbia hills and thus be quite as readily eroded as a salt-cemented dust deposit on it's floor.

[Bill Harris]

Light-toned layered and widespread deposits on Mars are not unknown: the "type feature" that come to mind is the Whiterock Formation of the crater Pollock (google "whiterock mars" for more info). This feature is a series of light-toned, finely-layered and somewhat erosion-resistant unit that is visible in many areas from Syrtis Major to Meridiani. When I first saw it from MOC imagery my initial thoughts were "ah ha, carbonates or evaporites!", but it turns out that it is apparently neither and probably more interesting. I'd suspect that the Homeplate Formation may be in that same class.

Folks are thinking evaporite because of our experiences at Meridiani and because sulfates have bene found at Arad and other sites. That can be easily answered once we get to the Homeplate outcrop.

>seem in some way jumbled, maybe much of them are debris deposits like ejecta blankets.

Reflect on the history of the area: Starting with Gusev crater, this spot has been impacted, flooded with lava and water and lava and water, sprinkled with ash and dust; indeed, the Columbia Hills seem to be the remants of a buried crater. This spite had a troubled childhood.

--Bill

[Guest_Myran_*]

CosmicRocker said: I wasn't expecting to see the basin basalt lapping up into this area, but maybe the "froth on the broth" did. If you had a large glass of beer (or a small one, for that matter), the bubbles would rise to the top, would they not?

Yes froth ends up on top, in volcanism its the material we call pumice.
But I dont think homeplate is volcanic, but agree with those who have suggested it might a crater. A year have passed after I first suggested it here, yet I still think it is ice that have altered the terrrain, scraping off the crater wall and created the feature we see here. So if this had been on Earth I would expect some of the material in Homeplate to be shocked quartz, now it might be something different, lets wait for a closer inspection.

[Bob Shaw]

Yes froth ends up on top, in volcanism its the material we call pumice.
But I dont think homeplate is volcanic, but agree with those who have suggested it might a crater. A year have passed after I first suggested it here, yet I still think it is ice that have altered the terrrain, scraping off the crater wall and created the feature we see here. So if this had been on Earth I would expect some of the material in Homeplate to be shocked quartz, now it might be something different, lets wait for a closer inspection.

The obliquity of Mars varies radically over time; polar areas currently support landcapes covered with frozen CO2, which is a sink for much of the atmospheric mass of the planet. So what happens to the landforms underneath the mantle of CO2 (and water) snow? We've seen more-or-less current erosion in north-facing crater walls from orbit, but what happens in flattish areas? Could HP have been eroded during a different climatic period caused by polar wandering etc?

Anyone got any thoughts on such processes, and how they might refer to the landforms we see today from the MER images?

Bob Shaw

[Guest_Richard Trigaux_*]

We have a model of Husband hills right on Earth, at Ries, Germany.

When we look at recent Moon craters like Tycho, we find that the bottom of them is filled with cowpat looking mounds, while the ejecta blanket shows lava lakes and chorded lava flows, perhaps less than some metres thick, closely matching the underneath ejecta form.

On Earth the Ries crater formed on a granitic substrate covered by about a hundred metres of limestone and shale layers. It is perhaps more recent than Tycho (38-30 million years) but more eroded. There is however still enough to see here, for tourists gazing from the central peak and think they are on the Moon. We find again a thin layer of lava (less than 10m) all around over the ejecta blanket. Analyzing this lava shows that it is the molten granite, and it fell all around the ejecta, and apparently AFTER it (some seconds I imagine). This lava also formed nice light-green glassy tektites 1000Kms away, known as moldavites. And into the crater, the cowpat mounds turn to be large blocks of sedimentary layers, lifted up, eventually overturned, but which fell back in place, shattered and torn, (jumbled sayd Edstrick) but with their overal sedimentary structure still recognizable (sometimes inverted).

So how this helps us to understand what are the Husband Hills?

It seems very likely that the Husband Hills are one of the "cowpats" which formed when the Gussev crater debris fell back on the ground. Of course other explanation are possible, but this is the most likely I think.

So the stratigraphy in Husband Hills formed BEFORE the Gussev crater, and it can be eventually very ancient, from the time Mars still had a plate tectonics, even back from the time it was still hot from formation, with many volcanoes emitting gasses and lavas (Husband Hills material are very likely all of volcanic origin). All these very ancient eruptions formed the Mars's southern highlands.

What happened to the Husband Hills after Gussev formation? Volcanoes seem unlikely at this epoch. Impacts are much more likely, there obviously was many, and perhaps 100% of the Gussev Hills surface was ablated by impacts. But the overal layered structure is still visible, and small impacts of this magnitude don't form lava. (So the lavas visible today are not from impacts more recent than Gussev).

But the main event was certainly the formation of the gigantic network of Ma'adim vallis. As far I can guess, there was short events (perhaps only one) but gigantic surges of water, and even more likely mudflows, and we known that such large mudflow can flow very far and form large horizontal surfaces. There is an example in the USA, near the Shasta Mount. This Earthy mudflow shows a region of small ridges perpendicular to the flow, and further a very large and flat alluvial fan, not much smaller than the Gussev plain. It is exactly what we see in Gussev! First parallel ridges barring the exit of ma'adim Vallis, and further a large flat land. We can even see the border of the alluvial fan skirting around Husband Hills and all the other hills in the vicinity! Spirit traversed this little downward slope just before entering the Husband Hills terrain. The land where Spirit landed, with the Bonneville crater and all, was the alluvial fan itself, and it showed to be just a muddle of blocks and sand, exactly as we can see in Earth's mud flows.



Does this tell us what can be Homeplate, the other smaller similar structures, and the darker mounds all around? I am afraid no. But it constrains the various hypothesis explained here by former posts in this thread. I shall say that Homeplate can be:

-A remant of a distinctive "sedimentary" layer existing before Gussev (I say sedimentary as it is layered, but it is more likely various layers of lava flows, pumice, tuft layers, etc).

-A larger block which fell here

-A remant of a VERTICAL volcano chimney (eventualy containing more unusual lavas, in the komatiites or trachytes families, see carbonatite family. Such volcanoes could have formed later than all the horizontal basalt flows we see everywhere, at a further cooling stage).

-Eventually this zone could be the true floor of Gussev, only the Hills being a "cowpat". When Gussev formed, it may have cut horizontally a vertical lava chimney, and eventually a whole system of volcano chimneys, with lavas of different composition, dykes, circular fractures, etc.

The problem with the idea of trachytic volcanoes is that they would be visible on all the southern highlands. But all the southern highlands were so heavily craterized that there is no hope to find traces of the original surface.

If Homeplate is formed of komatiites, there is some chances we find semi-precious stones like jadeite, metal ores, or even diamonds!!!! (But diamond form under continents, not likely on Mars).


I shall add here other phantasms, if I find more. What is there to earn for the one who best guessed what is Homeplate?

[Bill Harris]

That is a good analogy, Richard. I've learned to be careful about applying terrestrial analogs to Martian conditions, but I think yours is valid.

We approach to Homeplate plateau (or the crest of Mitcheltree Ridge, whatever) and we see scoria, basalt, sand and a sulfate (salt) sprinkle on the rocks. Imagine that...

--Bill

[Guest_Richard Trigaux_*]

That is a good analogy, Richard.  I've learned to be careful about applying terrestrial analogs to Martian conditions, but I think yours is valid.

We approach to Homeplate plateau (or the crest of Mitcheltree Ridge, whatever) and we see scoria, basalt, sand and a sulfate (salt) sprinkle on the rocks.  Imagine that...

--Bill

Thank you for your support, Bill.

I think it is not only an analogy: the same mechanisms are at work. Of course they will not give the same result, depending on atmosphere, gravity, etc... So we must be wary.


I already note that the crest of Mitcheltree Ridge is not layered, so it is not a native ground feature. Rather some process gathered rocks here, and there are many similar features in the surrounding terrains (around other hills in the vicinity, in place which were not covered by the mudflow). So I think it is an important feature which existed in many parts of Gussev crater before mud filling. It is too linear to be impacts, it has too large blocks to be dunes, and water erosion cannot give this. It either don't look like cowpats. My best guess would be that the Gussev impact hit a thick ice layer, among other terrains. When the whole thing fell back, there was large ice blocks, and the spaces between them filled with loose stones and sand. After, this exposed ice melt or sublimed, lefting those curious small ridges and mounds where there was spaces between ice blocks.


Another "phantasm" I will add here is that homeplate would be a piece of hard sedimentary rock. When the highland formed, there was perhaps permanent water or things like that. So it would not be a surprise to find hardened sedimentary rocks, hard ones to bear the shattering and keep large dimentions: sandstone, and even limestone. The later would be a good find.