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

[dvandorn]

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

[Bill Harris]

I do recall that when Spirit first topped Husband Hill and we saw the Pitchers Mound feature, my first impression was to refer to it as the Cinder Cone because it looked like one. Although misleading, incorrect and loaded, the term was used by many of us until the name"Pitchers Mound" came to be.

I think just about all of us will be suprised in a few Sols, even those of us who are correct.

--Bill

[vikingmars]

In fact, at the beginning of the mission, Pitcher's Mound (not yet named) was seen by Spirit team as an interesting figure to explore (also referred as a "cinder cone"), because from orbit MOC images it did not showed up as a "cone", so this was a real discovery...
Well at that time, it was still a dream to go there !
Here are :

- the 1st good view of this "cone" feature from Bonneville's rim
http://marsrovers.jpl.nasa.gov/gallery/all...00P2287L6M1.JPG

- its last good view, just before reaching the the Columbia Hills
http://marsrovers.jpl.nasa.gov/gallery/all...00P2425L7M1.JPG

Enjoy !

I do recall that when Spirit first topped Husband Hill and we saw the Pitchers Mound feature...

--Bill

[Shaka]

- its last good view, just before reaching the the Columbia Hills
http://marsrovers.jpl.nasa.gov/gallery/all...00P2425L7M1.JPG

Enjoy ! 

Man, There's something else this photo reminds us. There weren't any "spongebob" rocks on that side of the hills. If they're impact ejecta, they can't have flown for miles!

[Bob Shaw]

I bid for 'Baby Mound' as the Official Martian Native Name of the mini-version of PM to the right of HP!

So: what are we looking for on HP?

Sounds to me like, apart from in-situ compositional data, we're looking for visual evidence to back up various lines of (ahem) enquiry. Trouble is, many of the processes which lay down beds will lay down bedding which will look very similar to those produced by a variety of such processes, except in the detailed detail. A 'smash and grab' visit to HP may not be quite enough.

In many ways, HP is a bit like Endurance, and would be worth while spending a l-o-o-n-g time investigating - and perhaps spending the winter near (there must be a good slope, facing in the right direction, where Spirit could do some nice long Mini-TES sessions).

I want to clearly see the contact between beds, to look at the detailed structures, and to see right round the whole shebang. And the rest!

Bob Shaw

[ElkGroveDan]

I bid for 'Baby Mound' as the Official Martian Native Name of the mini-version of PM to the right of HP!

If you look at a diagram of a baseball diamond, the feature next to homeplate would be the "On Deck Circle".

[Bob Shaw]

If you look at a diagram of a baseball diamond, the feature next to homeplate would be the "On Deck Circle".

What's 'baseball'?

Is it like... ...Rounders?

(All your base(ball) are belong to us!)

Bob Shaw

[Shaka]

HEY, Who let 'Jolly Jock' in the gate?
O.K. We're gonna do this; we're gonna do this right !



And there ain't no Baby Mound!
You could look it up.

[Bob Shaw]

HEY, Who let 'Jolly Jock' in the gate?
O.K. We're gonna do  this; we're gonna do this right !



And there ain't no Baby Mound!
You could look it up.

Do words like 'Silly' 'Mid' and 'On' mean anything to you?

Not that I actually *care*, you unnerstan', living in Scotland, see?

Now, as for Doug...

Bob Shaw

[imipak]

Do words like 'Silly' 'Mid' and 'On' mean anything to you?

I'm sorry, but you've given me the image of Geoffrey Boycott pushing his car keys into HP... "Well Ritchie, the air's cool and dry this morning, so the ball won't be swinging for Shane Warne. The wicket is very dry, too, so look for the pace men to have the ball lifting sharply off the basalt... especially at the Husband Hill End."

[Shaka]

I'm sorry, but you've given me the image of Geoffrey Boycott pushing his car keys into HP... "Well Ritchie, the air's cool and dry this morning, so the ball won't be swinging for Shane Warne. The wicket is very dry, too, so look for the pace men to have the ball lifting sharply off the basalt...  especially at the Husband Hill End."

Hey, Pal. When The Commonwealth lands a rover on Mars, you can use all the Cricket terminology you want!
Jeez, that game ... They don't even have real pitchers! One of the outfielders gets the ball, runs all the way in to the mound and kinda heaves the ball like a hand grenade! Naturally most of them can't even reach the plate without bouncin' the ball; foul balls count as runs, so naturally one batter can score like 7000 runs! Meanwhile out in the bleachers the elderly are passin' away, pregnant women are being delivered, and their offspring are learning to say "Well bowled." And this can go on for weeks and in the end the game can still end IN A TIE!!! I mean, Gimme a break!
And a tie is a good outcome for England; otherwise they lose to one of the island colonies like New Zealand or The Falklands....keeeriss...

[Bob Shaw]

Hey, Pal.  When The Commonwealth lands a rover on Mars, you can use all the Cricket terminology you want!
Jeez, that game ...  They don't even have real pitchers! One of the outfielders  gets the ball, runs all the way in to the mound and kinda heaves the ball like a hand grenade!  Naturally most of them can't even reach the plate without bouncin' the ball; foul balls count as runs, so naturally one batter can score like 7000 runs!  Meanwhile out in the bleachers the elderly are passin' away, pregnant women are being delivered, and their offspring are learning to say "Well bowled." And this can go on for weeks and in the end the game can still end IN A TIE!!!  I mean, Gimme a break!
And a tie is a good outcome for England; otherwise they lose to one of the island colonies like New Zealand or The Falklands....keeeriss...

It's at times like this that I'm really glad I live in...

...Scotland.

Bob Shaw