"Twin Craters" = San Antonio. There are images of San Antonio West scheduled for 2196.

Well, arête is usually an erosional mountain feature, as you say, and what we're seeing is a deposition feature feature, so a different term is apporpriate. Isthmus is probably neutral in this regard.

I think the best term is septum, "a partition separating two cavities or spaces". This is the term used on the moon for a ridge between two adjacent craters.

I think we're talking about a ship from Magellan's expedition. Rui, you're the expert, what do you think?
http://en.wikipedia.org/wiki/Victoria_(ship)

Arête, as you write it, is a french name which means "ridge" and is more likely to be applied in mountains, not in this case.
Now, if you use it in English (like it's written here), I cannot tell.

Yes, looks like it, although I was expecting to see the rest of Magellan's fleet used to name more proeminent features...
Looking forward for Santiago!

The rarity of twin craters on Earth means that the terminology for describing them is poorly developed. "Arête" is probably workable: English isn't shy about using words from other languages (ref James Nicoll). 'Septum' doesn't really work for me, I tend to associate it with anatomical structures. However, if its the accepted term of art, so be it. 'Divider', or 'dividing ridge' seem most descriptive, if unimaginative.

I wonder if its possible to look at the pair and figure out which hit first, or from which direction. Even a few milliseconds difference in arrival time would, I think, produce a difference in shape.

CE

I agree (while rubbing my philtrum, under my septum, with my finger.)



I would have thought that things would still be "up in the air" at a few milliseconds after the first impact, during crater formation. But it will be interesting to see the details.

Andy

If I understand correctly Bill's post 143 about directed shockwaves in mine blasts, I think "already moving but not yet up in the air" might describe it better.

Hadrian's Wall looking good over there, Dan...

Click to view attachment

... but not much else to see... this might be a flying visit....

Unfortunately no new views of the Twins in the latest downlink. But we're seeing many versions of some images - I don't recall ever seeing the "product version number" become a letter, like the "A" at the end of the filename of this image:
http://qt.exploratorium.edu/mars/opportuni...VRP2597R1MA.JPG
(Very cool image, I think, with the tracks veering to the left in the choppy see of dunes...)

If Concepcion was in the order of 10^4 years old, do we have an estimate for the age of the Twins? An order of magnitude older? Two? Older still? (presumably impact features like this fill up with dust eventually)

Right, fredk, Oppy's been having some trouble with the uplink to the relay satellite and I guess that the "product version numbers" have gotten around to exceeding "9", so they've gone alpha. Anyone "with connectionc" care to venture a guess why?

The ripples have gotten to look like choppy seas, I don't thik this is a effect of the cratering at San Antionio since we've been seeing this since we arrived at Concepcion. We "crested the hilltop" there and are headed downhill-ish so I think that this is an orographic effect.

--Bill

Why has all the dust from inside San Antonio West (and East?) been blown out in one particular direction to form a single big dune? Other craters on the same HiRise image don't look like this has happened to them. It doesn't seem to me like the result of a gradual process but rather the effect of a strong wind that blew for a short time, temporarily revealing Hadrian's Wall. Then there's all those choppy dunes - another localised phenomenon. The relief around here is really slight so I can hardly believe that orographic effects alone would produce such striking changes. I have no explanation to offer but I think it's at least worth considering whether something unusual could have happened here fairly recently in Martian terms (post San Antonio but pre Concepcion).

EDIT: Think Tunguska - flattened trees but no crater. A big tornado might also do the trick; we don't really know what happens on smaller scales inside Martian dust storms.

All aboard the Opportunity Express. Next stop... Santa Maria. Woo-woo!
Well, I can hope...

Brian

How safe does it look like for the Rover to go inside this crater to investigate any exposed bedrock???

Dust death trap--no way!

My sediments exactly. (insert snare-drum rim shot here!)

Arête is a geomorphology term with glacial implications. It is a ridge formed between two cirques or two U-shaped glacial valleys. As such, it is probably inappropriate to use it to describe the ridge between these two craters.

About as safe as it looks for Kevin Bacon to walk across a stretch of open desert...




You should be ashamed of that...

There isn't a name for a terrestrial equivalent to this feature. What we have here is a feature created by the combination of two ejecta curtains being simultaneously emplaced. We probably need to draw from whatever terminology has been created to describe crater ejecta features-- I shudder to think at the Latin/Greek/archaicEnglish that would get cobbled together for that term.

"Isthmus" is as good as anything. But in keeping with naval terminology, p'haps it can be called a gangplank?

--Bill

I do believe "Septum" is the correct term , as I said in Post 152. Septum is used in lunar morphology, and also terrestrial volcanic craters. If you Googgle "septum crater" you will find several examples of this usage.

Don't worry, people - soon the wretched feature will be far behind us.

Phil

Click to view attachment
"The elongate crater Torricelli near the north margin of Mare Nectaris was
probably formed by two simultaneous impacts as indicated by the partly
developed septum at A."http://history.nasa.gov/SP-362/ch7.2.htm

Actually, it already is by a few meters, because Opportunity is now positioned at the east crater.
Pictures should be available soon.

Sounds like a good plan. The ejecta is eroded, the rock in the southwall is not in-situ bedrock but exhumed ejecta. Nothing to see, move along folks. We'll get the images downlinked. Eventually.

However, just for curiosity, it would be nice to have a Pancam set of the mysterious prancha de grupo between the craters...

--Bill

I have to say this is one of the prettiest craters we've visited - here's east twin:
http://qt.exploratorium.edu/mars/opportuni...I4P1977R0M1.JPG
Drive direction pancams are looking SE, but could this be a reason to linger: is that a piece of impactor just inside the near rim?
http://qt.exploratorium.edu/mars/opportuni...I4P1977R0M1.JPG
Also notice the big, tall pile of ejecta at the far end of the isthmus/septum/gangplank.

A really fine set of images from a much more satisfying vantage point than the previous stop: should make a spectacular panorama (as Stu prophesied). Definitely one for the full treatment and a place on the wall. The septum will be immortalised - septum in saeculo saeculorum!

There is a look at Eastern Twin with tracks leading to previous vintage point by Western Twin

Click to view attachment

Not a bad view after all...

Better to come from others, I'm sure...

http://twitpic.com/1c1fle

Yes, not a so bad view actually

Even has an ice-cream cone lying on the sand there!

Here is a 3-image panorama of the Navcams today (Sol 2197) of San Antonio, exaggerated 3x. Interesting structure in the craters.

--Bill

The isthmus would have been an easy drive after all.

Also a drive into the crater(s). They do look like Eagle crater in terms of aging, don't they?

Thanks Damien!

I'm glad Oppy didn't land within driving distance of Valles Merineris...

"You know, if they're really careful, I'm sure they could drive Oppy down there to the floor..."

Just joking. Oppy is an explorer, her mission is to see new things. But sometimes it does feel like one of those episodes of Star Trek: Voyager, where they spot a swirly, angry, clearly dangerous, potentially starship-devouring "spatial anomoly" and Janeway beams "Let's go take a closer look...!"

Reminds me of the opening segment of the old 1960's TV series, Mission Impossible: "Jim, your mission, should you decide to accept it..."

But seriously, there is the need to anthropomorphise our Intrepid Explorers. We assign gender, have a mental image of a WALL-E bopping around Mars on a tour. Nothing wrong with that, the Rovers are an extension of all of us. Though, I imagine, a psychologist would have a field day...

Just as when we were younger, Oppy may have also been inclined to try hazardous things in the name of exploration. It is amazing that we all survived adolesence. Now that we and Oppy are "6-score and whatever" we tend to be a bit more careful.

[/philosophical_mode]

I would like to get at the edge of rim for a closer view of That Rock...

--Bill

It looks like a cat. Not just in shape, but how and where it's sitting (right Ted?)

Waiting for Opportunity!

There's two tiny stones on the dune to the far left of Ant's wonderful panorama. They're bound to be called Vladimir and Estragon. They they are, sat on the surface of Mars for perhaps thousands and thousands of years, not sure what's going to happen, every day the same old same old, when - all of a sudden - a rover trundles past...

Andy

Oh yes, Beckett said it right:

"In an instant all will vanish and we'll be alone once more, in the midst of nothingness!"

Almost unsettling how close he got it!

If it's a cat, it looks like a black cat. I wonder if Oppy's hazard avoidance abilities include not crossing black cats' paths?

Here, kitty kitty!
http://qt.exploratorium.edu/mars/opportuni...I4P2404L7M1.JPG

Now the question is...who left the damn cat in there? (first post but long time reader)

Twin craters = twin blueberries: http://qt.exploratorium.edu/mars/opportuni...PGP2936M2M1.JPG

1M299696631EFFA3PGP2936M2M1= Sol 1932, way way back at Erebus....

EDIT: oops, got timestamp and Sol# confused...thanks, fredk

http://www.greuti.ch/oppy/html/filenames_ltst.htm is a useful filename decoder...

--Bill


PS-- Look at the blocky nature of That Rock. We gotta look closely at this one (I'm sure to get Shunned...). Need to go out this evening, but we've got an L257 Pancam of the rock and isthmus-- have fun.


http://qt.exploratorium.edu/mars/opportuni...I4P2404L2M1.JPG

Black Cat Rock...

Click to view attachment

No shunning here, Bill, I'd like a look too.

Not quite as far back as Erebus, more like Absecon/Reeds Bay, not far from Block Island.

Maybe we shouldn't be surprized about finding a cat - remember Steve the cat who came to Mars on Phoenix?

It is still fairly chunky with JPEG artifacts but here is a cropped enlargement, with some increase in saturation, of the L257 Pancam trio of That Rock on Sol 2198. Not any detail to be seen on the shadowed side, it's dark and somewhat bluish which doesn't do much in the faint reddish Martian skylight. It appears to be another erratic rock on the plains, probably much like the Marquette Island rock.

--Bill

If on closer inspection it is obviously not a piece of typical Meridiani rock, or obviously not another iron meteorite, it may call for a couple weeks stop to identify it. The drive straight to it looks a little scary (slope plus sand) but it looks approachable at a slant from the side.

We could hope it's another interesting rock from far away to add to the catalog, or we could hope it's nothing new so we can hit the road without delay. I'll leave it to each and all to look within for which is the more pure and honorable hope.

--- Full quote removed. Mod. ---

I hope that Oppy will not venture into any more craters other than Endeavour. The cat looks very inviting, but remember how difficult Oppy found the drive out of Eagle crater.

The recent pictures of the hills around Endeavour look very inviting.

My hope is that after Oppy has spent a year investigating the hills around Endeavour crater then it will start another impossibly long drive right down into Endeavour crater to look at the clays.