Endeavour Crater, And again shall we conquer the Remoteness Options

[JayB]

"The objective for June remains the same: "Drive. Drive. Drive," said Squyres."



http://www.planetary.org/news/2009/0531_Ma...ate_Spirit.html

[MarkG]

In trying to understand Meridiani and the Endeavor rim, I keep the following things in mind...

1) The profound ancientness of the Martian surface.
2) The significant variability of the Martian atmosphere. Perhaps a third of it freezes and sublimates yearly, plus secular orbital and axis changes indicate periods of different conditions over time, plus injections and depletions by volcanoes and large impacts, plus highly variable dust content further obscures the issue. The presence all over Mars of ventiform terrain features whose formation is beyond the transport capability of the current atmosphere underscores this.
3) Any surface water would likely be either ice or ice-covered most (if not all) of the time, even in ancient Mars. Ice-dominated or periglacial shorelines is what one is likely to see. For Meridiani, the interplay between surface ice and very concentrated brine underneath is important to consider.

So, with the above in mind, I follow the rovers and the orbiters, and try to see how various ideas fit with the unfolding observations.

One of the things I keep thinking about it the "planed-carved-like" slopes in Victoria crater. The surface around the rim was either flat, a planed-down slope of 15-35 degrees, a cliff, or debris beneath a cliff. If the surface was covered by ice sheets that were seasonally mobilized by brine at their base, these ice sheets (or their large cracked pieces) would creep down slopes and effectively plane them.

Did this ice come from seepage from below or from precipitation from the atmosphere? Was Meridiani always equatorial? Fun questions.

Seeing the rim deposits of Endeavor may shed some light on this. Or pose more questions.

[ngunn]

One big problem with the Meridiani Sea is that there's no big depression to hold it. The area is on a regional slope.

the interplay between surface ice and very concentrated brine underneath is important to consider.

I have no idea whether or not this is relevant to Meridiani but one thing does connect the two posts quoted. Subglacial lakes do not need to be in topographic depressions - a slope will do just fine if the overlying pressure distribution is right. The plug'ole may be iced up! Subglacial hydrology and landforms are never far from my thoughts when looking at Mars.

[Phil Stooke]

Ngunn's point is really good - and I don't see this getting prissy! - subglacial lakes might be allowed. So might regional crustal tilting, though it's a bit ad hoc. Personaly I prefer it all to be ground water, which might possibly make it to the surface in local low spots, either as concentrated brines which could remain liquid, or under an ice cover. I just don't see much chance of any big seas in this area.

Phil

[MahFL]

I just don't see much chance of any big seas in this area.
Phil

We had subtropical jungle in the arctic circle on Earth, so anything is possible, given time.

[tty]

We had subtropical jungle in the arctic circle on Earth, so anything is possible, given time.

Even a little better than that. During the early Eocene (c. 50 million years ago) there were alligators on Ellesmere Island (about 79 degrees north, and about the same then). This suggests that arctic temperatures were a bit over 30 degrees warmer than at present. Oddly enough equatorial temperatures were only slightly warmer than now.

[Phil Stooke]

"there were alligators on Ellesmere Island"

Now they have to wear Tuques, even in summer.

"anything is possible"

I'm afraid that really isn't true, and many things that are possible also didn't actually happen.

Phil

[ElkGroveDan]

My fault for bringing the term "sea" into this discussion.

Now let's get back on topic please.

[centsworth_II]

I thought that the rim of Endeavour consisted of sulphate rich sandstones with a similar appearance to those found so far. They may have been excavated from much lower in the 1 km thick stack of sulphate rich sandstones but would look very similar to an untrained observer to those found so far.

I don't think Endeavour's rim will consist of the same rocks we've seen so far. The previous examples were in small craters excavated in those sandstones. My impression of Endeavour is that it's an old crater, part of the cratered terrain underlying Meridiani Planum. I think it's being exhumed by the removal of Meridiani Planum materials, but its rim materials will be very different.

I'm a little ( ) confused.

Does everyone agree that the layers of Meridiani Planum extend 800 or so meters beneath the surface that Opportunity now sits on? (I'm not saying that all those layers are of the same composition.) If so, that would mean that if Endeavour predates those layers, the visible peaks of it's rim would have been a kilometer or so high when first formed. Does that sound right?

[serpens]

If we accept that the hematite signature is indicative of then upper layers of the sedimentary deposits then Endeavour certainly predates those deposits. Only the remnant rims do not have a hematite signature. In contrast the crater to the SW has an ejecta blanket covering the deposits which means it postdates the sedimentary deposition. Or maybe had an ejecta blanket high enough to preclude any groundwater near the surface. Or was fitted with some form of surge resistance. (Ok moderator I smack my own hand). The exciting thing is that the rim remnants of endeavour are old and would represent the basal layer beneath the sandstone . They would be great to investigate up close. I wonder if Oppy has Spirits mountain climbing genes?

[CosmicRocker]

...Does everyone agree that the layers of Meridiani Planum extend 800 or so meters beneath the surface that Opportunity now sits on? ...

800 meters has been quoted as the thickness of the Meridiani Planum sediments in some papers I've read. I don't recall if that was an average thickness or a maximum, but regardless, the thickness is almost certainly not constant. One would expect the thickness of a package of sediments laid down on the eroded surface of some basement rock to be quite variable. The thickness would be great over deep basins, but thinner over basement highs. The rim of Endeavor is a very significantly uplifted region of basement rock, so I would expect the sediments to thin greatly toward the rim. To answer your question more directly, I would guess that the visible peaks were uplifted at least a kilometer above the average height of the surface the Meridiani sediments were deposited on.

[AndyG]

I would guess that the visible peaks were uplifted at least a kilometer above the average height of the surface the Meridiani sediments were deposited on.

This paper would suggest a total crater depth of just over a kilometre for a crater 22km in diameter.

How high above the Meridiani surface are the rim peaks, out of interest? (I can't find a handy figure).

Andy

[tim53]

A Meridiani Sea is only possible if:

a: One invokes a former topographic barrier that is now gone
b: ...a subsequent regional tilt of the terrain (on a grand scale, since the deposits are vast)
c: dare I say it: An ocean in the northern plains that puddles up to this elevation.


The "bathtub ring" feature around the rim mountain in Endeavour that was shown above is interesting. When I first saw it, I got all excited, because it STRONGLY resembles shorelines in the Lake Bonneville basin.

...but all it took was HiRISE stereo to convince me that that's not what this feature is. It's not level OR planar. It appears to follow the gently rolling topography of the sulfate deposits overlying Endeavour, so it's more likely it's a remnant of one of these layers that has been preserved at the base of the mountain for some unknown reason while the rest has been eroded away. It'll be interesting to see what it looks like on the ground.

As always, the Real Mars turns out to be more complicated/interesting than our first impressions would suggest!

-Tim.

[ElkGroveDan]

The "bathtub ring" feature around the rim mountain in Endeavour that was shown above is interesting. When I first saw it, I got all excited, because it STRONGLY resembles shorelines in the Lake Bonneville basin.

Thanks Tim. Now I don't feel foolish any more. The old geologist in me can now raise his chin a little higher again.

[tim53]

Thanks Tim. Now I don't feel foolish any more. The old geologist in me can now raise his chin a little higher again.

Absolutely! This is the great thing about geology. Especially now, with Mars. Unlike the 20 years post-Viking, when we would hypothesize and not have a chance to shoot holes in each others' hypotheses with much substance, now we can send a rover over to check it out!

-Tim