"Could the Meridiani Spherules be Surficial?" Options

[djellison]

It seems that you have decided to cut off Dr. Burt's thread.

Indeed - Dr Burt agreed it was the right thing to do - it was going in circles and getting no futher. The same is true here - but given that this thread has been going for less time, I thought I'd give it a little longer before bringing it to a close.

In both cases - the threads have been more of a cyclical soap-box rather than scientific debate - and that's not something I want at UMSF.

Doug

[tglotch]

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.

Kye,

The oxidation reaction that you hypothesize would not produce hematite, but rather maghemite. High temperatures (such as might be produced by impact) could oxidize the magnetite to hematite. However, as I think I've mentioned before in other threads, hematite formed by the oxidation of magnetite produces an infrared spectrum that is inconsistent with what is seen by TES and Mini-TES.

[Kye Goodwin]

tglotch, re your post 47, Thanks very much for your response. My amateur attempt at describing at a hematite creation process has not produced a good model. May I call upon your expertise to answer a few questions on related topics?
I have been wondering what we know about the three occurrences of hematite at Gusev Crater: the hematite-rich coating on Mazatzal and hematite detected in Pot-o-gold and Halley. Do we know if the crystal structure of any of these hematite minerals resembles that of the Meridiani spherules?

Apologies for the following questions. They are too general and also leading, but I hope that you might comment.
Is there any way that hematite could form at Meridiani from the available minerals in the dust, soil or rock under climate conditions that have prevailed relatively recently in Mars history? Could such a process produce the type of hematite crystal structure that the spherules display? If grey hematite could form in a cold sub-surface aquifer, is it conceivable that slow limited aqueous processes on the surface could accomplish the same result over a longer period of time?

[tglotch]

Kye,

The occurrences of hematite at Gusev were detected by the Moessbauer spectrometer and not seen by Mini-TES. This implies that the hematite there is not coarsely crystalline like it is at Meridiani.

As for Meridiani, we don't know the exact mineralogy of the dust, but we know the Fe-bearing phase is magnetite. See my above post for my take on the magnetite-to-hematite transition.

My view on the hematite formation at Meridiani can be summed up thusly: thermal IR data from TES and Mini-TES rule out a high-temperature formation mechanism. In addition, there is no reason to pose an exotic formation mechanism under current conditions when there is plenty of evidence for past aqueous (however short-lived) activity. Breakdown of Fe-sulfates in the outcrop is to me the most reasonable mechanism to form the hematite spherules.

[Kye Goodwin]

tglotch, Thanks for that information about the hematite at Gusev (your post 49). I guess that it doesn’t have any obvious implications for the origin of the spherules at Meridiani.

I am seeking a low-temperature formation mechanism that could operate under recent Mars conditions because for me an “exotic” process would be one that requires a warm Mars. It is still an extraordinary claim that Mars once had a climate that would allow liquid surface water or near-surface groundwater. The MERs have added no evidence of persistent surface water. They have discovered overwhelming evidence of water-catalysed chemistry, but no structural evidence of beaches, lake-bottoms, channels or water-tables that put the chemical activity in an Earth-like context. Those are very likely impact sediments at Meridiani.

We have seen far too much evidence of water chemistry for it's origins to lie mostly in a brief warm period early in Mars history. In the Columbia Hills the evidence of aqueous chemistry is complex and mystifying, so much so, that it is now being explained as water interacting with volcanism, but again there are no clear signs of bulk liquid water. Volcanically heated waters must be fairly rare but I think that much of Mars surface will turn out to be as chemically complex as the Hills. Water chemistry has been happening there in slow Martian ways over the whole history of the planet.

[djellison]

....in your opinion.

It's time to bring this thread to a close.