Dawn thoughts...
It is one Martian year since the Martian fly-by and orbit boost.
Dawn would need to be within about 2 million kilometers of Vesta for Vesta to appear bigger that a point to a human eye observer at that distance. It is about 3 times that distance now.
Question: What will be Dawn's velocity relative to Vesta when it enters Vesta's Hill sphere? (An approximation will do...a bit too complex to figure out myself on just one cup of coffee...)

It seems to look like the Santa Maria crater might have only exposed buried rubble (not layered sediment). If this turns out to be true, that the impactor slammed into a rubble deposit, not the layered sediments that we (well, Opportunity) have been traveling on, then we have some interesting things to think about.

Are we in the fill of an older crater represented by the broad depression we are on the West side of?

Have we crossed into the planed-flat zone of the rim ejecta from Endeavour? If deposition of the sediments continued after the Endeavour impact (likely), then some sediments would accumulate on the outer rim. If the whole thing then erodes flat, we would have an area of ancient rubble, planed flat, with perhaps a bit of additional sediment over it.

Better views, especially of the near (west) side interior crater wall, will help resolve this.

A sharp lookout for different rocks is a good idea.

Just before Santa Maria, there is a downward dip in the terrain corresponding to a sinuous outcrop line leading off to the NE and SW. This could represent some sort of real geologic boundary (maybe the edge of a layer we will be below as we continue East). This edge is easily seen in the satellite pics, and the slope zone is seen in the elevation maps.
I will wager this boundary gets some rover attention, which could be frustrating to some, with the Santa Maria crater beckoning just a short distance beyond...

"Anatolia's"
We have not seen such a long, dramatic, and open, crack in the ground since then--the first months of Oppy's mission. There seemed to be hints of them in this area, but nothing to "fall into". Has anyone seen a scientific treatment of this feature, plus any relation to the ground we are currently traversing?

We simply do not know what has spalled or broken off of this rock.

The large number of crater interiors and other steep south-facing slopes in various equatorial areas with deposits of dark sandy material bespeaks of some sort of episode in the Martian past that would transport and deposit this material. An interesting problem.

Of note is that Victoria had dark windblown material blowing from inside its northern rim. Maybe the dark stuff (as dunes up against the North rim?) is there too, but buried by more-recent dust and debris except where a few spots are eroding....

Although it is likely that MI is ejecta, it is not definitive, and may never be known with certainty. It cannot be ruled out that MI could have been ejected into space for a period of time before recapture, or even came from a parent body other than Mars that we have insufficient knowledge to recognize.

(Marquette Island was a secondary meteorite from elsewhere on Mars, and it was a Gabbro -- Coarse-grained Olivine + other stuff.)

Re: Intrepid Crater

It is interesting that this small crater displays (in a modest fashion) the same erosional forms as Victoria -- "Capes and Bays".
Santa Maria might be likewise categorized.

Messenger is pulling away from Mercury for the last time. As Messenger approaches perihelion, Mercury is just past aphelion, so it will pull father away for a little while. But soon after Messenger passes perihelion and begins its last solar orbit before insertion, Mercury will close the gap, and the following perihelion will be orbit insertion around Mercury.

Any results in the Vulcanoid search? Will there be another round of searching during this last independent perihelion?

The "Slot" -- what is it?

Opportunity is now rounding the corner of a large area of low-albedo surface that roughly resembles an elongated rectangle stretching 3-5 km to the NNW, towards Victoria. I've been curious as to how this feature arose and persisted, and to see if there is anything on the ground that the rover passes over that would give a hint.

Has anyone heard any discussion of this?

I have my doubts about wave erosion and shores, at least of a free liquid water surface during the briny times Endeavour was formed. I think Mars was too cold by then, any body of water would be mostly ice-covered. I do think that an ice-layer (maybe thin) over brine is worth considering. There could be a situation with the Martian atmosphere below the water triple point, but wet brine would exist under ice bound to the soil. If the brine started to pool, it would then evaporate, but the soil would stay wet, but no (or few) actual liquid pools. This wetness could mobilize the overlying ice layer if on or near a slope, and a little erosion could occur (remember the ramps and headlands of Victoria?). The rim of Endeavour has a different composition and is above the local water table, so it would have a different history. And any soil water would not have the same brine content. It would erode/be-overlain differently.

Remember also that Meridiani is not like many other areas of Mars, no other area of extensive Hematite anywhere near its size exists on Mars (there are a smattering of smaller areas). So its history is not the same as the ancient northern ocean.

...well, my odds of successfully urging a spacecraft are far better than successfully urging an entire planet...

Mercury is about to pass behind the Sun in its pursuit of Messenger at the halfway point between the 3rd flyby and orbit insertion. Mercury is at periapsis and Messenger at apoapsis. Go Messenger!

In regards to the discussion in the previous thread concerning the "geo"morphology of the benches around the Endeavour crater rim hills, this is one case where many possible explanations will be resolved [maybe] by the ground-truth of rover examination.
My personal working idea is that there were periods characterized by seasonal ice cover, which would be sometimes mobilized by bottom-ice-surface melting/brine-ing, which led to the ramp erosion seen in Victoria. On a larger scale, that could lead to some features seen on the Endeavour rim, which have some glacial-looking aspects (thinner ice, in the scenario I'm thinking of). They could be evaporite or wave benches, too, but the situation remains murky (and mostly below freezing, too).
We will also be descending from the rise we have been traveling on into darker-looking stuff, which may be the darker sediments seen a few feet down the the craters examined. One wonders if the pavement will be quantitatively different there.
Looking forward to the unknown...

Dawn is now closer to Vesta than to Mars. A small thing, but it marks the cruise approach to Vesta. Go Dawn!

Over the next few months, Mercury will appear to go back-and-forth relative to the sun as seen from Messenger, as the planet and probe travel their elliptical orbits, with Mercury slowly lapping Messenger. The back-and-forth-relative-to-the-sun motion marks the dynamics of passing through the halfway period of the "lapping", with Messenger doing 5 orbits to Mercury's 6, between the third flyby and orbit insertion. Just a chance for some Keplerian visualization cheap thrills...

...The anatomy of a crack, and a very dirty one. Likely a result of dessication shrinkage and debris (mostly blueberries, plus general Martian dust) filling, with evidence of multiple episodes of some sort of degree of re-hydration cementing things a bit.
We see again how the passage of time preferentially concentrates the hematite nodules while the sulfur-salt-sandstone matrix is powdered and blown away.
The extreme friability and tiny particle size of debris powder of the Meridiani substrate create some interesting questions. We have seen dunes of the sulfur-salt stuff only on places like the rim of Victoria, where the rate of production and concentration of the sulfur-salt powder is relatively prodigious. Where does it go? Some ideas...
1) The Meridiani hematitie/sulfur-salt plains occur only on a small percentage of the surface of Mars. Its eroded dust thus becomes just a trace constituent of the general Martian dust. It is just diluted to near-invisibility.
2) The sulfur-salt dust could be a preferred nucleation site for precipitation. Snow nucleus. This would systematically remove it from the global dust inventory over time.
3) There could be some sort of very slow chemistry going on between these sulfur salts and the Martian atmosphere. This might also influence how it erodes. It could be driven by some trace atmospheric constituent or even solar/cosmic radiation side effects.

Anyhow, these are some thoughts that the Concepcion MI's have brought to mind. I don't have good access to journals (I do read articles I find out about, by the way) or daily bull sessions with grad students, or full access to all the results of the instrumentation, so maybe this has been covered already. This forum is my scientific coffee break, about all I have time for. I hope the working scientists don't take offense, and will be glad for the display of interest in the details of their work, and forgive the speculations-based-on-inadequate-data that come out of this forum.

In guessing the age of Concepcion (and developing a geomorphic age scale for Meridiani craters), one must keep in mind the non-linearity of processes at work here. Dune migration has already been shown to be likely episodic.

Another type of phenomenon not yet discussed is the de-hydration of once-buried debris. If there is any residual moisture or hydration in the excavated rocks, it will be exposed to wider temperature and lower effective pressure, and will rapidly evaporate, perhaps causing shrinkage as well (look at the tiny cracks on mini-Wopmay). This erosion may occur rapidly in even a few days (or seasons), and then tail off. But it would generate a lot of deterioration of the excavated debris relatively quickly, and then things would slow down.

The result of this may be big error bars in certain age ranges in our Meridiani crater-dating scale.

From this pancam picture...

http://qt.exploratorium.edu/mars/opportuni...66P2369L2M1.JPG

...there is a real nice example of a fully-mineralized crack in a fragment of ejecta....

This answered some of my questions, too. It seems that the changes in Mars' orbit and axis are on the scale of 100,000 years (rather than my statement of tens of thousands), so the profound ancientness of the surface is again reinforced. Comparing Concepcion with Fram and Resolution Shows Conception to be younger (Fram has significant dune formation around its rim, and Resolution has much ejecta partially buried in dunes).

Given Conception's very fresh appearance, but with no white sulfur powder and the presence of a few small NE-SW oriented "dunelets" of very fine material, the 1000-year proposed age for Concepcion seems very reasonable.

Now, can anyone our there tell if this is a crater of a very-fast-moving small impactor, or a a slower-moving larger impactor (i.e., a primary or secondary crater)? Does the appearance of the crater give sufficient information?

In evaluating Concepcion, the main efforts will be in the Geomorphology (as stated above), plus a look-see for any evidence of the parent meteorite body. (There might also be an APXS exam of the sulfur-salt pavement fragments to see if composition is changing during the long traverse.)
One of the interesting aspects of this crater is the "disturbed" look of the nearby dunes. They seem to still bear the scars of the seismic shock and the impact of debris from the impact. It is reasonable to speculate that no major dune-moving wind event has occurred since this crater was formed. There is an implication that dune-moving high wind events only occur during a different climatic period than Mars is in now, perhaps only every few tens of thousands of years (due to variations in Mars' orbit and precession of its axis). About the only thing missing from the site (from immediately after the impact) is the very fine and light white sulfur dust from the fragmentation of the pavement.

now, THAT is a handy little gadget... Thanks!


Now here is a question -- if Spirit's arm was extended more towards the right, it would make a small, but maybe helpful, difference in the center of gravity towards the uphill side... Has this been considered?

Most of those rocks are most likely blasted-out chunks of the Meridiani substrate. However, if a few shards are Marquette-Island-like, that would be very interesting...

Hope for a cleaning blast on the Mini-TES...

As has been noted, the current surface of Meridiani that Oppy is driving over has some fairly large irregularities in the surface of the Sulfate-salt sandstone pavement. What could cause this difference? What differences in the compositional structure and/or erosional pattern would yield this difference?
Oppy is climbing towards a ridge (or emerging from a broad depression) that is near the location of Fresh Crater, hence the nearby horizon). Better sight lines towards Endeavour Crater may await us.
I am antsy with anticipation to see if some of the fragments littering the ground around Fresh Crater show the signature of Olivine...