Agree completely. Mars is still very water-rich, but almost all seems to be in ice. In terms of the observable surface though, after cessation of the (Late) Heavy Bombardment you might say that Mars "freeze-dried" (in part owing to lowered atmospheric pressure). That is, martian surface ice tends to vaporize, losing heat, except near the poles or at lower elevations (where it can transiently melt before vaporizing).

---HDP Don

What, if anything, can be inferred about the history of the density of Mars' atmosphere from these deposits? A correlation between the apparent decline of atmospheric pressure & the planetary magnetic field would be interesting if true, and the layering observed in Meridiani appears to offer some capability to refine the timeline of these changes to a significant degree.

Thanks Emily! As always, you have illuminated the paths of further knowledge. I take it most of these atmospheric effects would happen post-impact. One can imagine the spray of ejecta ~ including a bunch of water ice ~ changing in mid-air. Still, the shapes of the ejecta from the Rampart craters look watery.

Back to the topic of this thread: does elevation have any bearing on dust/sand levels? What/where is the zero point, or sea level, on Mars?

Hi all! I was just wondering if this crater differs much from "Fram"-crater? And if, in what ways? Just a beginners question!

I asked that back here in this same thread and got some input.

Aha!!! That was some interesting reading, thank you centsworth_II!

ditto! It's fun to see everyone's youthful postings from six years ago.

The mini martians have built a seige tower for the assault on the Chocolate Hills...!

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Mmmm.... chocolate.
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"...Run away! Run away!"

Yes, it looks like "drying up" happened quite some time ago, on the order of billions of years. Thus any impacts which hit liquid water are also necessarily happened long ago, and are heavily eroded by now. Also, I imagine underwater craters are eroded more significantly than dry ones.

I'm afraid we don't see any such craters by now. Even nearly-disappeared old craters like this one in Acidalia Planitia were likely "dry":

Google Mars: http://www.google.com/mars/#lat=29.343875&...5976&zoom=7
MOC image across the crater:
http://global-data.mars.asu.edu/moc/img/M04/01722

Note how many smaller craters it has. It is _old_.

However, as others point out, "drying up" was achieved in significant part by water hiding as ice underground. On Mars, underground temperatures are below 0 Celsius to depths of ~2 km even on equator.

No one knows how much dirty ice is hiding there, protected from evaporation by several meters of dry dust and rocks. Thanks to HIRISE, we do know that new craters as low as at 40 latitude uncover ice.

Therefore impacts even today can hit a very icy location and melt it, creating "splashes" and lots of water temporarily.

And looks like in places this water melted and evaporated, leaving huge holes in the ground. It should be easier on equator. Valles Marineris is nearly on equator.

Perhaps the most striking feature there is Hebes Chasma:
http://www.google.com/mars/#lat=-1.087581&...0200&zoom=8

It is nearly 200 miles long, more than 50 miles wide and about 8 km deep (!) in the lowest point, relative to rim. The volume of removed material is gigantic. But it has no outlets. Where did all this material go?

There are several more smaller (but still very large) subsidence features nearby which have no outlets.

I think crustal stress associated with the formation of the Tharsis bulge is a much better explanation.

UGH! Sorry, my last colourisation was hideous!!!! Didn't have access to my usual software. Do now tho...

http://twitpic.com/13ar2w

Crustal stresses were definitely involved. However it's very difficult to produce an enormous closed depression like Hebes in unbroken plains by tectonic stress alone- how do you stretch the crust enough in this one spot to make room for the collapse of 100,000 cubic kilometers of rock, without any more than minor fracturing of the surrounding plains?

John

Hebes Chasma: "It is nearly 200 miles long, more than 50 miles wide and about 8 km deep (!) in the lowest point, relative to rim. The volume of removed material is gigantic. But it has no outlets. Where did all this material go?

There are several more smaller (but still very large) subsidence features nearby which have no outlets. "

No outlets on the surface, but if ice melted under a cap of rock and drained through subsurface aquifers into Echus and then along Kasei Valles, it can still get out. I imagine a thick cap of Tharsis lavas over buried ice, heating from beneath related to Tharsis activity, and relatively slow collapse of the major chasma depressions as the water drains out through aquifers into the various outflow valleys. There are those pesky interior layered deposits, of course... I suspect mainly ash deposits from multiple eruptions, later cemented by ground water, like giant Home Plates.

But the main point of this is to say that a surface outlet is not required for a place like Hebes Chasma.

Phil

Hmmm. Think Oppy will want a closer look at this one...

Click to view attachment

3D view: http://twitpic.com/13mwa3

It's amazing how all the rocks are turned to the same angle, in a sea of sand. Have we been able to ascertain the status of any rocks buried deeper than this level of sand? Did we find some rocks peeking out from the cliffs at Victoria that answer this question?

I do not think that they were turned to the same angle.

I think that they are probably ventifacts. Ventifacts form when a field of rocks are all first sand blasted by a wind from a constant direction for a considerable time and then are sandblasted from a wind from another direction for another considerable time. An angular join forms where the two sandblasted surfaces meet.

EDIT: Spirit has seen more probable examples of Ventifacts. For example Spirit took the following photo of ventifacts as part of the Bonestell Pan:

http://mars.lyle.org/imagery/color/2-271689561-6.jpg

All the same angle? It looks like totally random angles to me.

Phil

You want angles? Here ya go...

Click to view attachment

Download... grab your funky glasses... zoom in and spend a few minutes wandering at leisure around this fascinating rock garden.

Off to work now.

Stunning view, Stu!

Here's another closer up stereo view of the lovely ejecta blocks:
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There will be more to add later, but here is the pan so far (taken on sol 2153) from Opportunities current location at Chocolate Hills.



James

I love these low-sun shots. This one was taken at around 4:30 pm local time, with the Sun only around 20 degrees up:
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Just been looking at that Fred, a lovely view indeed.

I liked the look of this view, with the robot arm over the Chocolate Hills, and the Sun dropping towards the horizon over there...

http://twitpic.com/13ybxj

Is it going to be safe to drive into the crater? How deep is the dust covering in the middle?

Not that there is anything interesting inside, but it would be the easiest way to approach rocks at the rim on the other side.

..... I don't think so.

Besides, the scientific objective is to explore as much of the rim as possible before moving on. There is no incentive to avoid circumnavigating the rim.

No it wouldn't. She would be stuck in the sand before reaching the other side.

I think that would be fatal. The interior is nothing but dust. You think Spirit is stuck--Oppy could easily get buried up to her solar panels. Now if we had one of those vacuum excavators, we could remove all the dust to show the crater much as it looked after formation. I would assume the dust has protected the rocks at the bottom from weathering, assuming dust influx was rapid compared to age. Anyone have an educated guess as to how long it would take to fill with dust. I would think less than 100 years with strong dust storms.

Edit: I'm a slow typist, by the time I'm done, two people have posted ahead of me

Yeah I've been having all sorts of fantasies about driving Opportunity into there.

I, too, am curious as to how deep it is. When is the last time Opportunity dug with one wheel?

Driving into Concepcion!?

No way, no how!

Endeavour awaits. Phylosilicates folks.

Craig

We'll all forget the phylosilicates when she shows us the wave-cut terraces covered with the sand and pebbles of Lake Meridiani.

Concepcion crater was referred to as 'fresh crater' before it got it's name. The reason it was considered a 'fresh crater' was because in the HIRise pictures it looked darker as if fresh material had been recently kicked up and had not weathered yet nor been covered in dust.
Looking at the latest images, it seems that Concepcion and it's rubble field is darker because the crater depression and dead air spaces between the rubble disproportionally collects *dark* colored dust, not because the material that has been kicked up is so fresh that it has not yet weathered to a lighter color or has not yet been covered by the light colored dust that is globally pervasive. I am not necessarilly saying the crater is old, just that aolean dust collection processes may have tricked us into thinking the crater is younger than it really is.

Another way to put it is that Concepcion appears dark and fresh from orbit because the rubble field and depression is trapping dark colored dust from miles away, not because the Concepcion impact kicked up dark colored material...
Make sense?

Yeah, I see what you're saying. Looking at the latest panorama, I can't convince myself that the sand in the area is truly much darker.

I'd say the dark dust is part of it. Definitely in the bowl of the crater. But in the ejecta field, it looks to me like the darkness is more because of the roughness of the ejecta. These big rocks and boulders cast really dark shadows (unless you're imaging from the Sun's direction). And many of them have very rough surfaces that also look dark, unless again you're viewing from the Sun. The regular Meridiani pavement is wind-planed quite smooth and level, so it looks bright.

Right after the impact, perhaps there was a coating of pulverized bedrock that would've been bright? Very young craters have bright rays (in some regions due to ice of course). I guess that light coating gets covered quick, but the rough ejecta field takes much longer to erode flat.

Rather nice new view of the Choc Hills...

Click to view attachment

...damn!!! Did not realize quite how fine the layering really is till this image; really amazing work, Stu!

Well, if you liked that you're gonna love this...

http://twitpic.com/147bb1/full

Hah! I like that little rock behind Chocolate Hills!

It looks like some kinda blueberry Chia Pet!!

That's a smashing view, Stu,
Would the "blue stuff" on the floor be ruled out as impactor material now, given the recent consensus on the crusty stuff atop choc. hills ?
Ta,
Eoin

I haven't heard about a consensus on the crust yet...

The crust and the blueberry's seem to have the same color, maybe its Hematite??

I hadn't heard of a consensus on the rind/crust either. Superficially it resembles the rinds seen a while back on a target called "Lemonrind." Lemonrind was later described as having a composition similar to the bedrock. This crust also resembles the fracture fillings seen in Endurance Crater at a target called "razorback." Neither of the previous rinds or crusts contained concentrations of cemented blueberries as these rinds at at Chocolate Hills do. Recall the Microscopic Imager pictures.

With so many concretions in the rind we might expect it to contain a lot of hematite. Attached is a right-filter, false color image from sol 2147 of the rind that should display hematite in a yellow color. It appears that much of the rind is composed of hematite, even the parts that do not display obvious spherules.

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Couple of interesting rocks in a new image...

Look at that very sharp little guy up there, top left...

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And this rock is just... odd...

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Thanks, Stu!

Is that an inclusion in the flat-top rock in the middle of the image, or is it a rind-fragment?

Today, sol 2161, it was time to say good bye to Chocolate Hills. Opportunity has started driving CW around Concepción.
Navcams: http://qt.exploratorium.edu/mars/opportuni...cam/2010-02-21/

Navcam anaglyph of the new view of Concepcion:
Click to view attachment

Here's sol 2161 navcam mosaic, pointing due south and showing the "ejecta ray" in the foreground.
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I know James and Ant will do much better when they get to work on them, but I had a go at stitching together the beautiful pancams that popped up on Exploratorium today, and I'm really chuffed with how it turned out... http://twitpic.com/14me2r/full

Some of the "highlights"...
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If the member of the MER team who decided to head for Concepcion is reading this - THANK YOU! I love this place!

The latest downlink includes a lovely L6 horizon sequence of our eventual destination:
http://qt.exploratorium.edu/mars/opportuni...CXP2378L6M1.JPG
I wonder if there are more filters to come...
Edit: Oops, should've posted in the Distant Vistas thread...