So nice to have you back !

Ciao, Paolo! Come vai?
Very glad to hear from you again!
Every time Oppy makes a turn, we're thinking, What is Paolo up to now?
I am so very pleased to know that sometimes we will be finding out in the future.
You cannot imagine how much that magnifies our enjoyment of the MER adventure.

We hear you loud and clear, Paolo! I echo the last comments completely. It is so good to learn something of what's behind the images we see, instead of just guessing like we often do here!

Are you able to enlighten us at all on what's behind the current choice of route? Science/cobbles, easier autonav, easier driving,...?

The route we are following should minimize encounter with Purgatoids. It will be considerably longer than a direct route but should be safer and maximize science return.

As for what I have been doing recently: for the past few weeks I have been busy on the other side of the planet trying to push a rover up a slope.

Paolo

Nice to see you back, Paolo. We'll take what bits of information we can get and not ask too much. So many questions come up along the way.

They don't build rovers so the wheels drop off after 601 m.......

This is great to have you back on the forum, Rover Driver !

As we say farewell to Victoria, here are a couple of long baseline stereo views of its cliffs, first from sols 1668/70 and second from sols 1682/83 showing Cape Victory:
Click to view attachment
Click to view attachment
It will be a long time before we have views this spectacular from Oppy again...

Seconded! (or is it thirded!).

I've been following UMSF since soon after the landings, but rarely
post. One thing I've been wondering about:

What sensors are available for autonav? I ask because a lot of the
time in the march to and from Victoria, it looked to me like a
'follow the trough' algorithm would have been useful. Oppy
seems to spend a lot more time trying to go between ridges
rather than cross them.

I'm under the strong impression (if I'm wrong, just stop reading)
that the MERs have tiltmeters. An algorithm which said, in effect,
'As long as wheel slip is low, steer gently towards whichever front
wheel is downhill' would allow Oppy to track along a trough.

just another back seat driver.....

ce

Just explaining an odd term for non-native English speakers: Purgatoids = larger ripples (dangerous dunes in fact)

For any newbies, we should add that it's not just an 'English-ism', but rather a Mars Exploration Rover-specific term. Purgatoids are drifts that look like 'Purgatory', where Opportunity famously got stuck for a long time.

Purgatoids from Mars -- I would buy that if it was a pulp sci-fi book.

Purgatoids - an irritation that can be diminished with some 'Preparation P'

This is an excellent question. When we talk about an "autonav" drive we intend a drive where cameras are used to observe the terrain around the vehicle and determine if there is a safe path or if the path specified is safe. This drive modality is pretty expensive (slower driving). You also mention "low slip". In order to measure slip, we need to use the cameras to measure the actual rover motion compared to the commanded motion (visual odometry). This is another CPU intensive task and it is used only when needed, either when we are on slopes or periodically on long drives (to verify we are still moving and not embedded in a ripple for example).

The rovers also have accelerometers and gyros (what you called "tiltmeters") assembled in an IMU (inertial measurement unit) that allows to accurately measure roll, pitch and yaw (RPY) of the rover. If you are interested you can google around and you will find which make/model and its specs. This sensor is turned on every time we drive and constantly provides the rover with the RPY, the rover "attitude". This information is important not only for driving but for communication (where to point the antenna) and cameras and MTES on the PMA.

While traversing the big ripples from Purgatory down to Victoria Anulus we used the IMU to specify safe limits on RPY but never used roll and/or pitch measurements to dynamically alter the rover's path. We have begun using RPY measurements to dynamically adapt the rover's path on both rovers only recently.

We also have sensors that report the configuration of the suspension system (rockers/bogies) and recently we used these measurements as well to dynamically modify the path or behaviour of the rover.

While it is relatively easy to come up with a strategy to drive between ripple crests, it is very difficult to ensure the vehicle will recognize an unsafe condition and stop. These new "smart" sequences quickly become very complex and difficult to prove safe in all conditions.

Paolo

"We will not see the like of those days again."

I learned a new word from the kids at work this week - "facepalm" - I'm still not absolutely certain what it means, but I can picture many geologically aware readers doing one in a moment's time, so apologies if this is a silly question. There seem to be quite a few protuding nodule-like features on Cape Victory evident in fredk's analglyph, including one right in the middle that looks almost like a freeze-frame of a cannon-ball smacking into a castle wall a few hundred years ago. Why might the slightly harder rock which erodes out in this way take a shape that crosses many vertical layers? And why might it be different from Duck Bay? Is there a terrestrial analogue?

No facepalm activity here. I was intrigued.

I'm not sure that I know the answer to your question, imipak, but I am going to hazard a guess at my peril. I think I see the features you are describing, and I believe they could be the result of wind erosion, temperature variations, and the three dimensional geometry of the fractures in the rock. I think it is safe to bet that the fractures in the rock were created by the impact that created Victoria Crater. If you look at the fractures on the face of Cape Victory (and in other capes and bays), you will notice that the bedrock has been broken into a lot of triangular and rhomboidal blocks.

At least, that's how it appears on the approximately flat faces of the capes. But, the fractured blocks are three dimensional, so many of them quite likely have pointed, pyramidal ends.

Erosion typically follows planes of weakness, when they exist in bedrock. In this case, it appears that some of the erosion is following the fractures. Fractures can also direct mineral-rich ground waters which can cause some parts of the rock to become harder or softer. Finally, since the fractures physically break the rock into separate blocks, freeze/thaw and/or diurnal, thermal expansion/contraction cycles can cause blocks of rock to move with respect to one another. I think your cannonballs might be the pointy, pyramidal ends of fractured bedrock blocks.

Sorry about the long and arcane explanation, but you did ask for it.

http://qt.exploratorium.edu/mars/opportuni...G3P2580L6M2.JPG


Are those Opportunity's tracks near Nevada in the top right corner of this image?

Phil

Good eye, Phil. I think those must be Opportunity's tracks. The alignment of the view across Cape Victory seems about right, and the shape of those markings nicely matches Eduardo's map of Opportunity's attempts to approach the cliff face.

Isn't it ol' Vicky :
Click to view attachment

That's not 'ol Victoria. That's a smaller crater off to the northwest, if I'm correct.

It's hard to make out Victoria from a distance, since it doesn't have any real raised rim. Here's an example of the view from sol 1686:
http://marsrovers.jpl.nasa.gov/gallery/all...00P1635R0M2.JPG

You're correct - it's not Victoria. Whatever it is, it was to the northwest on sol 1687. This particular image was taken on sol 1689.

This must be it (white arrow). I haven't seen a name for it.
Click to view attachment

Yep - that's got to be it.

Without wishing to disturb the blissful silence of our acute "conjunctionitis", now that Victoria Crater is virtually out of sight, yet before it passes too totally out of mind, we might profit from a thoughtful look at the recent paper in JGR-Planets which summarizes the state of mind of our esteemed PIs (some of them) concerning the processes which produced Vicky in the first place, to whit:
Degradation of Victoria crater, Mars
John A. Grant, Sharon A. Wilson, Barbara A. Cohen, Matthew P. Golombek,
Paul E. Geissler, Robert J. Sullivan, Randolph L. Kirk, and Timothy J. Parker
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, E11010, doi:10.1029/2008JE003155, 2
Ideally we would all have access to the complete paper before discussing its findings, but harsh reality prevents that for many of our members, so it occurred to me to liberally quote from the paper, limited mainly to substantive observations and conclusions. Those wishing details as to the methods of observations, raw data and figures, and discussion of alternate interpretations will need to visit a library, or at least request them here.
To begin, the basic descriptions:

The authors base their inference of the original dimensions of VC from the well-established model for fresh craters following the normal processes of collapse from the transient form. The original diameter is varied to fit that needed to produce, after erosion, the present crater in terms of rim height and width, thickness of ejecta remaining etc.

The flat annulus of VC, together with its serrated edge are, IMNSHO, its most distinctive features, not seen in thousands of other craters in other areas of Mars, on other bodies of the solar system, and through a wide range of degradational states.

The facts that impact melt is (apparently) absent, and that radially-oriented "tear faults" could have initiated the development of bays, offer the kind of specializations needed to explain the rarity of Victoria-type craters. Such characters may be a result of the 'weak' nature of Meridiani bedrock compared to other bedrock in the solar system.
Alternative scenarios are not supported. Some might ask, though, whether such features fully account for the rarity of the "cape-and-bay" rim form?

Finally, the authors suggest a character of VC which could explain the rarity of its occurrence, namely that it represents a 'snapshot' view of a (relatively brief ?) intermediate stage within a degradational sequence for Victoria-sized craters in the Meridiani area.
Other stages in the sequence may be represented by other craters studied by Oppy, such as Endurance (an earlier stage) and Erebus (later stage).
The successive processes in this evolution can be summarized as follows:
In concluding, note that the authors do not suggest the presence of frozen volatiles (i.e. water) in the Meridiani crust as an essential feature in explaining Victoria Crater evolution. This ingredient appears to be important in the formation of other Martian crater types at higher latitudes (e.g. pedestal craters), and it had figured large in a speculative scenario I concocted an age or two ago to explain Vicky, before we actually reached her. (Ignorance was certainly bliss!) I still think, however, that there are more questions remaining, hidden beneath her generous skirts, regarding her 'special' status among impact craters. I would, at the least, like to see a more thorough census of the rim forms of small craters on the Plain of Meridiani and other similar Martian substrata (e.g. hematite-rich zones). I can't be comfortable with only one or two examples of Victoriana.
YMMV
So who wants to instigate a discussion/argument/battle?
Conjunction still has days to go.

My impression from browsing MOC and HiRISE images of Meridiani was that these serrated crater walls are common in this area. In fact even Endurance can be seen as a small example, with just a couple of capes. I don't recall seeing them in other areas though, so thry may require the kinds of rock found here. I think the cemented sands just disintegrate over time, resulting in a lack of ejecta blocks on the rim, a limited population of large talus blocks below the capes, and probably causing undermining of the walls over time which hastens the formation of each bay.

Phil

I'd certainly like to see those other craters, Phil. Unfortunately, I can't work with the monster HiRISE files, and need someone to pare them down. I do remember from a couple of years ago a clear example of a serrated crater, indeed, a quite bizarre 'double-decker' with TWO concentric serrated rims.
But I'd be far happier with this hypothesis, if I could see a few more in the serrated degradation stage.

I will point out that Endurance is characterized by incipient "bay" formation that looks for all the world as if the crater wall had been undercut by erosion (likely aeolian) and the upper surface had collapsed in a sheet into the now-enlarged crater. This fits is rather well with the description of Victoria's bay formation.

-the other Doug

Shake: "example of a serrated crater, indeed, a quite bizarre 'double-decker' with TWO concentric serrated rims"

This one or something like it? A few examples across Meridiani Planum. Bizarre indeed!
http://hirise.lpl.arizona.edu/PSP_001348_1770

Astro0

Consecutive hits from a Shoemaker-Levy-like string of bodies?

How about a normal crater that blasted through two layers of rock with differing resistance to erosion?

The upper layer (with the bright white rim) is softer and got easily eroded and blew away while being expanded. The lower portion was more erosion resistant and maintained its shape over time. The inner "crater" is the lower portion of the original crater that was less eroded (thus less enlarged). The inner shelf is the contact between the two layers.

-Mike

Shaka - check these out: (they lead to JPGs, resolution reduced but still OK)

Here's a giant example:

http://hirise-pds.lpl.arizona.edu/PDS/EXTR...RED.abrowse.jpg


Here is a degraded example (top right):

http://hirise-pds.lpl.arizona.edu/PDS/EXTR...RED.abrowse.jpg


One big example and some smaller ones:

http://global-data.mars.asu.edu/moc/images/large/S0701971


Many craters, some with a few capes and bays:

http://global-data.mars.asu.edu/moc/images/large/E0500154


Similar one:

http://global-data.mars.asu.edu/moc/images/large/E0201844


Another big example:

http://hirise-pds.lpl.arizona.edu/PDS/EXTR...RED.abrowse.jpg


Phil

Good Lord, Phil, I never saw so many ugly, irregular craters in all my life!
If my experience with crater photos had begun with these, I would be struggling to explain the neatly circular craters elsewhere as the bizarre anomalies.
Compared to these, Victoria is a model of regularity; its 'teeth' are far more uniform around the whole circumference than just about ANY in your photos!
And I thought I understood impact cratering!
I have a headache. I think I'll go lie down.

Those appear to me to be more recent impacts into older sediments.

The impacts are likely in old sediments. But how do you know if the impact craters are recent?

Well...ahem...Conventional wisdom would say that the youngest craters had the simplest, circular, well upraised rim, and a crater depth to diameter ratio close to 0.2 (for small, simple primary craters). That would imply that just about none of the craters in Phil's photos are very young.
What does that tell us about "conventional wisdom"? That's why I have a headache.

Just a dark line on the horizon now...

http://roadtoendeavour.wordpress.com/2008/...rewell-victoria

(well spotted, hort! )

Yes I spotted it yesterday while stitching parts of the Santorini pan - it came as a nice surprise.

There is a very readable paper in the current issue (22 May 2009) of the journal Science summarizing the results of the exploration of Victoria, "Exploration of Victoria Crater by the Mars Rover Opportunity", by Squyres et al. No dramatic surprises, but a nice summary.

NASA Rover Sees Variable Environmental History at Martian Crater



http://www.jpl.nasa.gov/news/news.cfm?release=2009-088

The National Public Radio show and podcast Science Friday has a podcast featuring Steve Squyres that mention the paper.

Mars Rovers, Mars Water (broadcast Friday, May 22nd, 2009)

Researchers published new findings based on data collected by rover Opportunity during its exploration of Victoria Crater in the journal Science this week. The rock and sediment features in the crater, scientists say, indicate that liquid water played an important role in shaping a sizable area of the planet long ago. Victoria crater showed water-driven features similar to those found at other crater sites several miles away.


Direct Download of Podcast mp3 ( 8.3 MB )
http://podcastdownload.npr.org/anon.npr-po...r_104479138.mp3

Jack

Great listening, thx stewjack.