[X] My Assistant

[Kye Goodwin]

I have been reading the response to the reponse to impact-surge linked by Dr Burt in post 170. The MER team objects to the impact-spherule explanation because " The spherules are dispersed nearly uniformly across all strata." I agree that is a valid criticism. It is very much like Dr. Burt's criticism of the MER team's hypothesis, that spherule distributions are not consistent with any conceivable ground-water movement regime that should have controled the development of concretions. I agree strongly with this point of Dr. Burt's as well. Neither theory does a good job of explaining the distribution of the spherules. Also, neither theory does a good job of explaining why the spherules do not apparently disturb the bedding.

There may be a solution in a possibilty that I now raise with some trepidation. I think that there is a chance that the spherules are superficial, and not an integral part of the Meridiani strata at all. This probably sounds crazy to many readers, but before rejecting it outright remember that science is at kind of an impasse on this and could use a new idea. If the spherules are superficial this would explain a number of puzzling observations.

The layering at Homeplate and Meridiani is most simply explained by impact-surge. It is elegantly and inescapably explained by impact-surge. The impact-surge authors have also tried to explain the Meridiani spherules as part an impact event. If doubts are raised that the spherules are integral to the deposit, this would not in any way be inconsistent with the impact-surge origin of the layered structure. On the contrary, an objection to impact surge would be removed.

I intend to start another thread under Opportunity to discuss this question. The first posting should be mine and should be an organized outline of how it might be possible that the spherules have been mis-interpreted as part of the Meridiani layered deposit. I am working on it. If anyone wants to start in on me with the obvious objections, do it here for now. Maybe Dr. Burt would like to respond. No matter what the details of spherule formation in an impact or spherule deposition in the impact sediments, the very uniform distributions that we see are troublingly unlikely. Random distributions are possible from explosive dispersal but less likely than some kind of clustering because of the rapidly changing conditions in the surge cloud. The more-uniform-than-random distributions of spherules on rock characterised by MER-team analysis cannot be explained by impact surge.

[Kye Goodwin]

Doug, Yes, "How?" is now the heart of the matter if you have followed me this far. How could the spherules be surficial? I am advancing a sub-aerial concretion hypothesis, but others might think of other possibilities. I am not a chemist and cannot offer a detailed chemical model but I can make make some general points toward the possibility that hematite spherules could form spontaneously under recent or current surface conditions.

Many aqueous chemical processes have been proposed to take place in the Martian surface environment under conditions like the present conditions. There is a long tradition of surface-weathering discussion, from Viking weathering pits and Pathfinder rock-coatings to many phenomena discovered by the MERs. I could post a whole bibliography in time, but here are two. This Yen et al paper introduces the idea of weathering facilitated by a daily water cycle:
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1571.pdf
This Yen et al paper suggests a roll for recent water activity in the formation of rinds at Meridiani:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2128.pdf

My point is that scientists think that a variety of aqueous chemical processes are probably happening on the present-day surface. Is there a particular reason to think that hematite formation could not be among these processes? There is plentiful magnetite in the ever-renewed airfall dust. This could be oxidized to hematite by a spontaneous (energy-yielding) reaction if oxidant is present as believed from the Viking results. A chemist would have difficulty setting up the assumptions for a hematite-forming process because so little is known of Martian soil chemistry or the planet's diurnal water cycle.

If we accept that it might be possible for hematite to form, why would it form as tiny spheres? Why would it be sharply localized in any form? I can't offer any reason for the sphericity or localization.

OK, I admit that this is not a sophisticated or close-to-complete model, but I haven't resorted to mysticism. Maybe a chemist will comment. I think that I will continue to consider the surface-spherule idea because it is a possiblity that would explain much simply.

[djellison]

My point is that scientists think that a variety of aqueous chemical processes are probably happening on the present-day surface. Is there a particular reason to think that hematite formation could not be among these processes? .

No - not surface - the near SUB surface - and in one case speculated as being places that have been recently exhumed.

They're talking about alteration by thin films of water. You're talking about the deposition of hematite and sulphate rocks. If you're getting water deposition from frost - then it's pure water - not the sort of water that could leave rocks behind.

Dominating Meridiani is erosion. It's clear to see from the imagery. How you can propose that the surface is growing, and burrying Berries - I just don't know.

Doug