Apologies if it has been brought up before, but this intrigued me: I noticed in some of the horizon Pancam views that just came down from Sols 812 and 856, that there is a "double-bump" feature on the horizon that appears at the same place, at about 99 degrees azimuth. I went back as far as Erebus and the feature appears to be there whenever decent Pancam images are taken of that spot on the horizon. In the distance from just-after-Erebus to Sol 856, the position of this thing on the eastern horizon only seems to have changed by about 2 degrees, more or less.

By my crude math, two degrees over the distance from Erebus makes this thing a honkin' long way away, and that in turn makes it honkin' big. I leave it to the mathematically and cartographically inclined to determine how large a "honkin'" is.

So, to get to the point: Anybody know what this feature is?

Here are some views:

Sol 812
Sol 856
Sol 790

I'll have to switch to my other computer, the one with all the images going back to Sol 1, to see if this thing is still there, say, just after we left Endurance... Unless somebody already knows the answer, that is. Just something to help pass the time until we start driving again

Well, I went all the way back to Endurance looking for the thing. It doesn't seem to be visible before Erebus, I think because it is lost behind the local horizon. I think we've gained a good bit of altitude since Erebus. It might be visible from the south side of Endurance before Oppy went in, but I don't have time to check that tonight.

If anybody wants to follow up on this, here are the measurements the feature's ground-relative azimuth that I've found via MMB, so far. These azimuths are based on the info from the Pancam tracking database. I reckon the margin of error is plus or minus one degree (false pride, perhaps) on most of these. It's not exact because MMB doesn't project the images in exactly the right way - perhaps close enough, though.

On Sol 856 (724K), it's at 98.7 degrees
On Sol 812 (69##), it's at 99.5 degrees
On Sol 804 (69RR), there's something like it at approximately 100.7 degrees - it looks more pronounced, strangely, perhaps due to the filter? Error is probably larger in this measurement.
On sol 799 (69FJ), it's very hard to see, but might be there at 100 degrees.
On sol 794 (6900), it might be at 100 degrees
On Sol 789 (68Q9), very clear at 100.1 degrees, VERY clear in the L1 on Sol 790!
On Sol 774 (66MA), clear (I think) at 101.2 degrees in the L1

Michael, if I'm not wrong this is the distant feature I already identified 1.5 months ago here.
The double peak should be the northern rim of a huge (35Km) far crater.

Dilo, I think you've nailed this one.

To get all the measurements on one image, I made a composite of THEMIS VIS images ( V05194001 , V05556001, and V06305001 ) and positioned the start pixel based on an overlay of Tesheiner's routemaps. MHoward, your angle measurements cross-over in the general vicinity of the northern rim of the nearby 35km crater, as Dilo suggested.

Click through the image below for a full res version of the mosaic (without the lines).

You know, Dilo, Slinted, I think you are right. Thanks for tracking that down.

The edge of that truly massive crater Those hills are only about twice as far from us as Endurance is from Victoria... perhaps a worthy destination after Oppy is finished at Victoria?

Surely going east across all the dunes she's likely to find would only take, oh, 2000 sols or so....

P.S. Amazing work, slinted... I knew someone would rise to the challenge!

I ahve noted those double peaks also, yes the hills around this huge crater is a likely explanation.

And I agree with mhoward, the distance are enormous. But I dont think we need to ask ourselves what direction Opportunity should go after its finished with Victoria. East by Southeast it is.

'Big crater or Bust!'

I was searching this crater rim since we get out of Erebus, as there is some altitude gain since. But I was not searching in the right direction, and I was searching for something more hazy...

it is amazing to see clearly these distant features.

To go on this crater would be interesting, as if would perhaps allow to understand how the Jarosite deposits were emplaced.

When looking from Endurance, this deposit looks as if it was a solid regular evaporite deposit.

But when looking at overal maps of Meridiani planum, the Jarosite deposits look as if it flowed flowed, as something very thick but still slowly flowing. We can see in this crater (and in several other craters in meridiani) the flow-like overal pattern of the crater filling. The Jarosite even covered the real rims as a kind of mud which subsided after. And, on Slinted's image (a super interesting work I must say) how intermediate-size craters look obliterated as if dug in some kind of mud.

Can the jarosite-salt deposits really slowly flow? I thing it is not unreasonable to expect it, as it is a well known feature of salt layers on earth, which can form diapirs, and even "salt volcanoes" like in the Zagros mountain, Iran, where salt diapirs appeared on the surface and even formed glacier-like flows. But of course it is a medium to large scale phenomenon, a small scale salt block will not flow.
Try on Google Earth: 27°N 55°E, altitude 100ml for an overal view
27°3'40N 46°28'E altitude 12400ft for detailed view of one, even showing individual salt "volcanoes" (whitish) in a more conventionnal sedimentary (reddish) mattrix. (Of course there is some washing of the salt by rain, which lefts its sedimentary content in place)

So it can be envisioned that the Meridiani deposit is not in its original position. But if so, what is this original position? Did it flowed from a higher plateau? Did it erupted from underground? Did it formed directly as a salt deposit, of from the action of acid on volcanic cinders, as some suggested?

really looking at this crater would be interesting.

Since we know the distance, can't we approximately determine the height? (hint, hint)

The minimum height for visibility assuming the general lie of the terrain is flat would be about +_152m (given that the observer is 1.2m).
At that range (35km) each pixel would cover about 10m vertically so count off the pixels multiply by 10 and add to 152 to give an approximate height.

Using the formula given by helvick above, I calculated a height of approximately 192 meters for both hills from the sol 790 image. There is very large margin for error, of course.

Double-Bump = Twins?

(ducks and runs)

Bob Shaw

If that's accurate, then they're taller than the Columbia Hills. I wonder what we would find if we could actually go there, considering how different the Columbia Hills were than the surrounding terrain.

My working assumption for those smoothly "dimpled" craters that looks like the surface melted and sagged into a crater shape is that these features were entirely covered by sediments and the Meridiani exaporites covered them more or less uniformly. Then, as the "sea" or whatever drained away and the climate shifted, the sediments on top of and more specifically WITHIN the buried craters compacted, with the central portions sagging downwards into their current morphology.

The distant crater is largely buried, but the bumps appear to be crater rim topography sticking up through the Meridiani sediment stack. It seems beyond plausibility that Oppy could ever make it that far, but they would make a wonderful, absolutely crazy, go-for-broke superextended mission target.

beyond plausibility... many other things in this mission were beyond plausibility. Reaching Columbia hills... reachig Victoria... getting out of purgatory...

Reaching those hills would have several interests:
-giving a hint of the composition of the ground under the salty deposits
-looking for shorelines, as seemingly the hills are pricking out the jarosite layer, like islands out of the ocean.





So, it may be possible to derive the compaction factor, knowing the ideal shape of a crater, and beyond the thickness of the evaporites.

But a perfect vertical compaction would have left the shape of the craters. Here theses shapes are rounded, that implies some amount of horizontal movement.
If you look precisely the large surrounding craters, there are flow patterns in several, and also ghost craters, as if they were buried. This implies a vertical movement too.

Twins
Nico

I've been waiting for that large crater rim to appear above the horizon. I hope that this is actually it.

I've noticed, on the PIGWAD Crater Database, that the large crater has a Barlow Crater ID of 413. I do not know if the Barlow catalogue has any information concerning the altitude of the rim. It does not appear to be within the PIGWAD database (that I can see). Does anyone have access to that information?