Aussie - Without looking up the many references, such effects have been seriously suggested, for both the Earth (e.g., Sudbury, Canada, local) and Mars (e.g., Hellas, w.r.t. Tharsis volcanism on the opposite side), but cause-and-effect relations can be difficult to prove. For example, people still argue as to whether or not the "Sudbury Intrusive" represents impact melt, although most now accept that the "Onaping tuff" represents impact debris.

BTW, regarding the weekend discussion of water and ducks, you can probably make early Mars as wet as you want - just don't make it too hot (except for transient impact or volcanic heating, or local solar heating of dark rocks on the surface). Climate variation may have been more extreme than on Earth, but probably alternated between cold and colder. In this regard, not enough liquid water to attract ducks at either Home Plate or Meridiani, IMHO, although both were probably damp owing to steam condensation. I see no problem with liquid water condensates making drainage networks after huge ancient impacts or with local brine break-outs making transient outflow channels later, but only as special events. Ice was probably more normal near the surface.

-- HDP Don

Quick colourised Pancam panorama...

Ice above -20 often contains veins of liquid water kept liquid by impurities, this is the first stage of Dburts eutectic brine formation. If a piece of dark coloured rock is included in a piece of ice near the surface then sunlight will warm the rock, which will lead to these veins becoming larger and more numerous near the rocks surface. Many people here probably know this already, but if surface ice was present at home plate or meridiani in the past could this provide a source of rock altering 'dampness'? Wouldn't steam condensing onto a rock surface form ice (not right away perhaps but fairly quickly) at martian temperatures anyway? If this has already been discussed could someone point me in the right direction?

Here is the complete 360 degree panoramic view taken with the

L0 Navcam on Sol 1315,1316 and Sol 1317.

jvandriel

Thanks for the citation. Actually, if there is Ca in the brine (because CaCl2 brine is extremely hard to freeze, and Ca will be concentrated by ice freezing), last or eutectic freezing won't occur until below -50 C (close to avg. near-surface temperature for Mars). Steam condensing at low modern martian pressures (above the triple point of water, at least for higher elevations), can only condense into ice (frost, snow), unless salts are present at the surface of condensation, which could yield a brine film (i.e., dampness). Ancient Mars probably had higher atmospheric pressures, so salts might not have been needed to yield a condensate of liquid water (or dampness). In any case, preferential post depositional leaching of recrystallized chloride salts by frost or ice could account for the crystal-shaped cavities, and other porosity, seen in the bedded rocks, particularly at Meridiani. Sulfate salts would tend not to be leached by frost, inasmuch as none exhibit freezing point depressions greater than -5 C. Frost leaching of common chloride salts (with F.P. depressions of 20 to 50 C) might also account for the report that chloride content, unlike sulfate content, increased with depth at Meridiani. More than you wanted to know?

-- HDP Don

NICE stitch. I did a polar-and-pinch with it.

A bit more than I was expecting but I've no complaint! However it would help my understanding a lot if you could point me in the direction of a detailed explanation of frost leaching, as I've got only a vague idea of how it works and hence only a very vauge understanding of your reply!

Edit: I've no wish to turn this thread into an undergraduate geology classroom, but my usual sources (wikipadea and google) have let me down a bit on this one.

Marsbug - I'm pretty sure it doesn't belong in this thread, but the concept is pretty simple. When salt is scattered on winter snow or ice, the desired result is to melt the ice, but this imples dissolution (leaching) of the salt too - and that's what we're talking about here. Picture soluble salt crystals scattered on the surface of a road or sidewalk in the winter. If it rains, they'll be leached (dissolved). If it snows or frost condenses, they'll only be leached if the temperature is above their maximum freezing point depression (so-called eutectic temperature with ice). Because the freezing point of pure ice is 0 degrees C, that means that sulfate salts can only be "frost leached" above about - 5 degrees C or less, whereas NaCl salt (halite or table salt) can be frost leached if the temperature is above - 21 degrees C, and CaCl2 salt (used by more affluent or northern communities) if the temperature is above -50 degrees C. Is that clearer?

As regards Mars, various salts were scattered across the surface by impacts (and wind). Billions of years of frost condensation should have preferentially leached the chlorides (especially calcium chloride) into subsurface brines, but left the sulfates at the surface, simply because Mars is so cold. See the Knauth/Burt papers from 2002 and 2003 for more detail.

-- HDP Don

I haven't noticed dust devils in images for a while, but there is still activity, as you can see by the changes around El Dorado in these navcams, sols 1315 and 1325:
http://marsrovers.jpl.nasa.gov/gallery/all...37P0746R0M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...AQP1977R0M1.JPG

and these hazcams, 1323 and 1326:
http://marsrovers.jpl.nasa.gov/gallery/all...AQP1214L0M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...AQP1155L0M1.JPG

Anyone got any idea if Spirit is anywhere near the rock christened 'Mckay' again? I'd love some really detailed close-ups of that one...

If you look at the route map Stu you'll see we're right over the other side of HP from Mackey at the moment.

James

AFAIK this 360º panorama wasn't posted yet.
It was taken on sols 1323 and 1325 and corresponds to the current site, referred as "Texas Chili" on the latest status update.


BTW, Spirit is in the middle of taking a multi-sol color mosaic of this same area.

I noticed a couple of items in a recent pancam image:

[source image at]

http://qt.exploratorium.edu/mars/spirit/pa...AQP2279L7M1.JPG



The upper item may just be resting there with dust around it, but the lower one looks like a blue berry to me.

Here is TEsheiner's latest pan in polar format.

Phil

Really hard to say. That's the frustrating thing about many Mars images, including close-ups from the Pancams. You can see practically anything you're looking for. If that object were part of a collection of blueberries, you might expect to see some lying around on the surface, as a Meridiani-style lag deposit, and that confirmation seems to be lacking in that image. Now tell me what we're seeing in this Pancam image, also from today, in the lower left half. Is it dozens of blueberries, somehow concentrated on the eroding edges of bedding planes, and as a lag on the ground, or something altogether different? I have no idea, but somehow suspect (it's the innate pessimist in me) that we're not looking at blueberries:
http://qt.exploratorium.edu/mars/spirit/pa...AQP2283R1M1.JPG

Of course, the even more frustrating thing about Mars images is that we can't all get to drive the rover to check such features out.

--HDP Don