Sol 591 Panorama, 12x3 pancam of Inner Basin & Home Plate Options

[Tesheiner]

Yesterday the download of that 12x3 pancam mosaic (180 x 45 degrees) was finished, at least on the L7 filter.

Here is the result with autostitch (compressed and reduced to half size).

PS: This was the first of two panos taken to obtain a good stereo map of the inner basin. It was taken on L7R1, so no true colorization should be expected for this one. The second one (same 12x3) was taken on sols 594, 595, and 597 using L257R127 filters.

[dvandorn]

In this perspective, the "dark mound" behind Home Plate looks more and more like an erosion-resistant tongue of the rock beds uplifted when the Columbia Hills were formed. It has a strike very similar to the hills themselves, and its strike is also very similar to those of the other outcrops we can see in this view that poke up, here and there, in the inter-hill valley of the Inner Basin and up the sides of Ramon Hill.

Home Plate itself -- it looks very much, in this view, like the remnant of an old impact crater. The way it sits on a little pedestal in the middle of the basin, and the way the edges of the pedestal sort of peel down, just remind me strongly of a rockbed that's been deformed and brecciated by an impact.

Now, that fascinating non-circular ring that makes up Home Plate's perimeter -- well, if Home Plate was a crater that's mostly been eroded away, then that feature represents some kind of cross-section of the crater floor. Or possibly of a portion of the brecciated, shocked and impact-melted rock directly below the floor of the crater.

It seems to me that if the Columbia Hills were uplifted *before* Gusev became a lake, it's possible that craters within the uplifted hills (especially in valleys between the hills, like the Inner Basin) may also have filled with water. Home Plate may have been a pond within the otherwise high-and-dry Columbia Hills, fed by either rainfall or artesian water pressure through fractures leading up into its brecciated floor unit.

If so, Home Plate may be the most exposed version of evaporite outcrop available for examination within Gusev Crater. Especially, within reach within Gusev Crater.

Of course, it might not be evaporite. But it might be the cross-section of lacustrine materials, or even a layer of highly altered rock that used to lie within the Columbia Hill's aquifer. In any event, a close look at Home Plate might be the biggest scientific payoff of the entire MER mission.

-the other Doug

[edstrick]

DVandorn: "..... a close look at Home Plate might be the biggest scientific payoff of the entire MER mission."

Amen Amen! AMEN!

The idea that homeplate may be a remenant deposit on the floor of a nearly eroded impact crater is the most plausible idea I've heard so far, and matches my impression of it as a possible evaporite or lacustrine deposit.

[CosmicRocker]

You have got to know that Home Plate will be the next "major" target, after descending. If that turns out uninteresting (I can't imagine it will be uninteresting.), then I'd guess the prominent outcrops on the opposite hills may be next, unless some hypothesis makes that "promised land" enticing.

If I am following your thoughts, you are suggesting that a perched outlier of the hidden lacustrine rocks may exist here. That would be a most amazing discovery, and probably the ultimate accomplishment of Spirit, if it is true. I'm not convinced this is an ancient crater, but I wouldn't rule it out, considering how old these rocks are.

What I think I am seeing here are remnant layers with strikes that are roughly conformal to the slopes of the ancient hills, which suggests airfall deposition to me. I guess one could imagine a flooding and draining scenario that could have similar results.

Regardless, the trip to the bottom should be quite amazing, with many insights along the way.

[edstrick]

One thing I've been thinking the last few days: Home plate could be volcanic ashfall deposit, cemented in the bowl of a now eroded crater. Seems less likely, though.

[Bill Harris]

You have got to know that Home Plate will be the next "major" target, after descending.

Indeed. The more I think about it, the Inner Basin should have remained the primary target once the Hills were reached. But the climb up Husband Hill provided a thick section, so all was not lost.

<chant>homeplate homeplate homeplate<nochant>

Here is a color enhanced, 2x exaggerated view of Homeplate to mull over--

--Bill

[djellison]

Without that northern-slope to enjoy during the winter, we wouldnt have had a misison to go straight to Homeplate

As it is, now we have a healthy rover, with loads of power, and seasonal conditions about to start benefiting southern slopes....life couldnt be better

Doug

[edstrick]

going around the south side of the hill to the inner basin would have probably killed them. They did the north slope to tilt toward the sun and keep power levels high in the winter. They learned that trick while they were climbing the west spur.

[tty]

One thing I've been thinking the last few days:  Home plate could be volcanic ashfall deposit, cemented in the bowl of a now eroded crater.  Seems less likely, though.

I've been thinking on more or less the same lines. Could Home Plate be a remnant of the melt sheet in an impact crater that has otherwise eroded away?

tty

[Bill Harris]

Given the 25* axial tilt of Mars and the 14* south latitude of Gusev, Spirit would have lost only about 25% power due to the solar incidence (disregarding the loss of intensity from the orbital eccentricty). Although the need to face north my have been a consideration, it doesn't seem that Winter would have been a death-knell to Spirit. My thoughts are that they weren't getting a lot of science from the weathered basalt of Gusev Plain and needed to get a lot of positive results, quickly, which meant climbing Husband Hill where there were visible outcrops. Keeping on the basalt plain for possible geological wonders in the Inner Basin was a long shot.

But we are where we are and it's been a good ride...

--Bill

[djellison]

Spirit got very close to being dead during the Sol 300-400 phase - that 25% was an enabler to do science and mobility during that time - and the alternative - a southerly route with -25% power - WOULD have killed it.

Doug

[SFJCody]

Whatever Home Plate's origin turns out to be, I wouldn't be surprised if the real colour of the rock comprising it is much darker. Back on the plains lots of the flattish, horizontal basaltic chunks were coated in pale dust that gave them the appearance of light toned, sedimentary rocks.

There's no reason to believe that this won't apply to really large expanses of flat rock. Home Plate could be basalt.

[Bill Harris]

Homeplate and the layered deposits in the Inner Basin are indeed a light color. Look at the image in Reply #6 and this unit is not rusty-hued. If you look closely at the floor of the Inner Basin, there are light-colored boulders as well as dark and rusty-colored rocks.

We'll see what it is like when we got down to the bottom and thwack a chunk...

--Bill

[edstrick]

tty: "....Could Home Plate be a remnant of the melt sheet in an impact crater that has otherwise eroded away? "

I doubt it. Melt sheets are found in large craters, tens of km across and larger. In smaller impacts, my understanding is that melt is largely mixed with other ejecta.

Also, on Mars, whether or not there was water in or under the surface, there probably is some percent of water of hydration in minerals like sulfates. These will tend to turn into steam before you form melt, making it maybe harder to form melt.

[alan]

Part of the panorama for 594-597 (3x8 with one frame missing)