It seems reasonable that Endurance might be an old crater that once was completely buried in meridiani deposits and is now being slowly exhumed.

However, the question that I would like to ask is what the process was by which the meridiani sediments that once filled Endeavour to the brim were selectively removed from the centre of Endeavour crater leaving the deep hole that can be seen today.

Gale crater is an old crater that was once completely buried in sediments. However, in the case of Gale crater the sediments in the centre of the crater remain and it is the sediments outside the crater that have been selectively eroded:

http://marsoweb.nas.nasa.gov/landingsites/..._etal_Jun08.pdf

EDIT: I supose that it is possible that Endeavour was never fully filled with Meridiani sediments and so there would be no need to provide an explanation of how they were later removed. However, what this does imply is that if the line around the ancient hills was a shoreline then at that time Endeavour crater would have been a 500m deep lake.

OK that was my own exaggerated term. Even a "Meridiani Acid Swamp" would show evidence of a shoreline if a standing body of water did exist there. We shall see.

(And yes, the wacky theory I referred to was one that was not mentioned here.)

One big problem with the Meridiani Sea is that there's no big depression to hold it. The area is on a regional slope. Any sea would have gone down the plug'ole.

Phil

I'm with Elk Grove Dan. Nobody, and that includes Steve Squyres, has the definitive story on Meridiani, much less the rest of Mars. When I look at the layering -- and I'm sorry to use that term, but that's what's there -- I can't help but believe that it is the sediment resulting from seasonal processes in a shallow lake or sea. And if the area is sloped now, that doesn't mean it was always sloped -- ever heard of the Rockies? And if it was a shallow lake or sea, then there may well be remnants of a shoreline. So back off and let people have a little fun with this site -- it's getting WAY too prissy.

Further research is indicated. And as luck would have it...

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



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

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.

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.

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

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.

"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

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

Now let's get back on topic please.

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?

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?

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.

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

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.

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

I don't know of any published values for that, but if you bring up Mars in Google Earth 5 and go to Endeavour Crater, you can browse surface elevations by watching the XYZ readout at the bottom of the screen as you move your cursor over the map. I'm not certain, but I assume these are MOLA derived elevations. Doing so, I roughly estimate the rim peaks to range up to ~100 meters above the regional surface. The deepest part of the excavated crater basin is ~ -500 meters.

The HRSCview map of Endeavour was posted around here before: link

The geometer in me shouts, "I can measure their height myself!" Or at least put a lower limit on their height.

All three bits we see now appear similar angular heights, but the east rim is farthest away so that's the greatest vertical extent of the rim that we can see now. Using this image of the east rim, and a distance of about 33.5 km, I get a height of about 85 metres for the part we can see. Of course we're likely not seeing the full extent of this bit yet, so that number will only climb as we approach...

If the far rim is 33.5 km distant and that is what we are looking at then another 160m or so is below the horizon at the moment.

That is not a very strong argument against it being an old shoreline. Old shorelines are often deformed by subsequent earth movements. Even the shorelines of Lake Bonneville that you mention are about 150 feet higher in the central part of the basin compared to the edges because of isostatic rebound after the lake disappeared, though this is not obvious because the change is very gradual.
In a more seismically active area like Italy the level of the shoreline from the prevous interglacial (just 125,000 years ago) varies from +170 to -130 meters.

I thought a few months ago people here were giving estimates of up to a 1,000 metres or more for the far rim of Endeavour.

But now these estimates have hugely dropped. So the rim of Endeavour is now only expected to be 100 metres above Meridiani? That's a tad disappointing...

We are waiting for the next big one here withing the shores of Lake Bonneville. Something like 1 in 500 chance of a 7.0 any given year. I'm in a 105 year old masonry house right near the fault... so let's hope you're right.

I have been wondering how much isostatic rebound might affect Mars... but does there need to be a mantle underneath?

Here's an image of Antelope Island with wave cut platforms in (the former) Lake Bonneville. I bet Stu could give it that Meridiani look, and maybe that's what we'll see when we get to the rim of Endeavor.

EDIT: Never mind Stu. I took a whack at it. Maybe Endeavor will look like this.

ElkGroveDan, that's a very neat picture -- it doesn't take too much imagining to connect it with Meridiani!

And here's something hot off the press from the Imperial College of London which supports the possibility of large bodies of water -- whether you want to call them lakes, seas, or oceans -- having once existed on Mars. The link is as follows:

http://www3.imperial.ac.uk/newsandeventspg...-10-59-30#fni-2

Their thesis is that the Late Heavy Bombardment added huge quantities of water to the surfaces of both Earth and Mars. I quote briefly:

"They found that on average, each meteorite was capable of releasing up to 12 percent of its mass as water vapour and 6 percent of its mass as carbon dioxide when entering an atmosphere . . .Using published models of meteoritic impact rates during the LHB, the researchers calculated that 10 billion tonnes of carbon dioxide and 10 billion tonnes of water vapour could have been delivered to the atmospheres of Earth and Mars each year . . . However, researchers say Mars’ good fortune did not last. Unlike Earth, Mars doesn’t have a magnetic field to act as a protective shield from the Sun’s solar wind. As a consequence, Mars was stripped of most of its atmosphere. A reduction in volcanic activity also cooled the planet. This caused its liquid oceans to retreat to the poles where they became ice."

And tim53, re your "ocean in the northern plains that puddles up to this elevation", take a look at the thread "Earthlike Mars?" (in the general Mars area), which is really about the Oceanus Borealis. (And which thread now seems to be connected, thanks to tim, to the entire subject of Meridiani!)

I'm curious about the sample spacing in the MOLA data. Hopefully, someone more knowledgeable of the dataset will comment. I am trying to understand if the narrow rims of craters like Endeavour might be under-sampled in the MOLA dataset.

It appears that the MOLA elevation models were derived from measurements made on areal spacings of up to 1/128th degree. At the Martian equator, 1/128th degree = ~463 meters. I found a reference suggesting that some MOLA data might be sampled up to 1/256th of a degree, yielding twice the resolution, or ~232 meters/pixel.

Considering that Endeavour's rim ridges are roughly a hundred to several hundred meters across, it seems unlikely that MOLA was able to capture many measurements at the highest peaks around the rim. If that is the case, the MOLA elevation model might under-represent the highest elevations of narrow ridges such as crater rims. I can imagine that fancy interpolation algorithms can partially compensate for under-sampling, but I wonder just how confident we can be with regard to the MOLA-modeled elevations.

The numbers you mention just describe the "resolution" between sample strips, Tom. There is also the question of resolution along the strip -- i.e., what was the interval between laser returns?

Also, "resolution" isn't exactly the right term, I think -- the *spacing* between sample strips is anywhere from 1/128 to 1/256 of a degree. The actual width of the strip of terrain from which a laser return is detected is somewhat narrower than that, I believe. So, instead of having a constant "pixel" coverage of laser returns, there is a matrix of laser-return dots which represent terrain elevation data, but for which no single dot "touches" any of its adjacent dots. In other words, there are from tens to several hundreds of meters of terrain between each sampled "pixel" and the next closest "pixel."

Think of it this way -- go to a plot of land 25 km on a side, lay out ten lines 250 meters apart and 25 km long. Walk along each of those lines and take an elevation reading every 100 meters or so. Then plot all of your elevation readings as a series of dots on a grid. That's the raw MOLA data. (Totally unsure about the spacing along the lines, but ~100 meters sounds about right, at least for illustration purposes.) Add in beam spread, and you can see how difficult it was to create elevation maps from the data.

I believe the pretty maps that the MOLA team created *all* used smoothing algorithms to present the instrument's data as general elevation maps.

-the other Doug

As Doug said it's hard to make any sort of generalizations with the MOLA data - you have to look up the individual strips and see what they covered specifically in order to decide if the processed data set might have missed any significant peaks or dips in any specific area. Over the whole planet the total mission sampling averaged about 6 points per square km but if a particular sample strip crossed a point of interest there could well be more points than that - the nominal "resolution" of each track was one sample every 300m and each sample covered an on track distance of 120m. In very rugged terrain (such as Endeavor's rim) it would certainly be possible for MOLA to have measured altitudes that are in the range of 100m lower than the actual maximum altitude of the peaks, possibly even more. To be more certain you'd have to find the specific MOLA tracks and see what they actually did cover.

The spec's on MOLA are available here.

Thanks guys, for your comments. I see how the actual location of the track on the ground is critical. You've confirmed my thoughts, though, that the data spacing is large enough that many, or even most peaks on the crater rim would have been undetected by the sampling. That PDS instrument profile for the laser altimeter was very enlightening. It had this to say about mapping resolution:
A 1/32 degree by 1/32 degree square is ~1850 meters on a side! Since all the orbits cross at the poles it is easy to see how the sampling density increases towards the poles. Since Endeavour is near the equator, the sample density there is likely to be lower.

I hope so. There is at least four old beach levels in that picture, and possibly a fifth.

Regarding DTMs, don't forget there's Mars HRSC coverage of this area too.
http://hrscview.fu-berlin.de/cgi-bin/ion-p...p;code=52692150

This may have been asked before, but does anyone know whether MARSIS or SHARAD might be capable of mapping the contact between the Meridiani sandstones and the underlying basement rock?

Speaking of shorelines, I'm sure most of you know that there is yet another recent paper indicating the presence of lakes on Mars. Here's the link:

http://www.colorado.edu/news/r/7e9c22ec0cd...4ed2e29f16.html

It's a fault scarp. (see my post in "Earthlike Mars")

-Tim.

For fans of Iazu crater here's a Google Earth overlay of moc frame m1001349. Click to view attachment
It's not sourced from a map projected version of the image so the registration isn't as great as it could be but when crudely draped over topography data it does give an OK overview of the differences between the older, shallower Endeavour and the younger pedestal crater to the south. Check out that deep stack of sediments at Iazu's north rim!


Why not use a proper map projected version of the image? Because then I'd either have to put up with a conspicuous frame or set the frame to be transparent. Doing the latter would require altering the image file, so I would no longer be able to link to an image already available online!

I think we can barely see a new part of Endeavour in these navcams just on the left of "Cook":
http://qt.exploratorium.edu/mars/opportuni...G6P1994L0M1.JPG
http://qt.exploratorium.edu/mars/opportuni...NVP1994L0M1.JPG

Waiting for pancams.
I think a peak north of "Cook" could match (far rim or east rim) . Any idea Rui or James ?

P1994 is a single frame, single eye navcam frame I asked to take at the end of each drive since we left Duck Bay. Every drive sol in the same direction, roughly pointed at Endeavour.

Paolo

I think you are right, there does appear to be a faint hint of a feature 6 - 8 degrees from the north end of Cook. Measuring the angles I think it correlates to this on the HRSC image:

Click to view attachment

In Google Earth this does look to be the next highest feature on the east rim after Cook.

James

Got it! Now I understand the "MovieFrame" in the sequence name.
Anyone wants to have a try building the movie up to date?

I've been collecting these L0 navcam frames and was meaning to ask about them. Do they serve a purpose such as photometry/sky imaging/characterizing the terrain under uniform lighting/etc, or are they just providing a regular view of the approaching rim of endeavour?

Btw, the R0 navcam jpeg frames from the jpl site are always cleaner than the L0 frames. This R0 frame shows a similar view to those two L0 frames:
http://marsrovers.jpl.nasa.gov/gallery/all...EZP0705R0M1.JPG
I think there is a very subtle feature there.

Nope, their sole goal is to document the approach to Endeavour. I'm sure someone can make scientific use of it, but the idea was just that, documentation of the approach.

Paolo

A very good idea Paolo. At what horizontal distance from the highest rim will the frame be filled from top to bottem on the Navcams ?

James...everyone knows that's Molyneaux...
Click to view attachment

Heck, I can't keep up - here was me thinking it was Hicks...

http://www.unmannedspaceflight.com/index.p...st&p=137625

James

Hicks is where Cook tells him to be...