Concerning the fog: Mohlmann elaborates in another article quoted from below (http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1120.pdf ) that there may be a specualtive “photon-driven iron-carbon cycle” that uses water absorbed from the mist as a source of metabolic energy for a hypothetical martian ecosystem. Iron is present, as is light, so at least some of the parts of his model are there. He suggests that hypothetical microbes adsorb atmospheric water from the mist. This is not at all impossible, (there are beetles that do much the same in the coastal deserts of Africa). The hypothetical microbes then take the water in through water channels; he calls them aquaporins (this is off, aquaporins are membrane the proteins in the kidney and other places that allow animals to recover water from their urine). The water channels close later in the day (or whenever) , trapping the water inside the hypothetical microbe. It is very ingenious.

It also leads to a possible testable prediction. Iron in the cell does not just float around. It is captured non-covalently, either by iron-sulphur proteins, or in porphyrins (such as heme). Light gathering systems in most terrestrial cells (except, I think, purple halobacteria) consist of a metal ion (on earth it is Mg) chelated in a pigment (chlorophyll) and surrounded by accessory pigments, (e.g. carotenes, phycobilins) each of which contains extensive conjugated double bond systems (e.g. 12 in chlorophyll a). Chlorophyll has a very characteristic action spectrum (high absorbance from 400 to 500nm, little from 500 to 600 and then a peak in the red; hence-obviously- chlorophyll is green). A Martian biochemical light-gathering system based on iron would most likely be surrounded by an equivalent system of extensive conjugated double bonds, like chlorophyll and the accessory pigments. A light gathering complex will either be black (absorbing all wavelengths equally) or coloured (absorbing some wavelengths preferentially). This should be detectable, and just looking at the Mars Express photos, it is pretty clear that there are valleys that are apparently pigmented, such as the so-called “sediment” in the early Reull vallis photos. It is important to know what this stuff is.

Clearly there are huge problems; a simple chemical cycle does not make a cell. It is also very cold, but Mohlmann has this one covered; it appears there are bacteria that live in the Antarctic permafrost, and are busy using iron to fix CO2 to organic carbon. So, while the model is extremely speculative, it is not impossible.

THE IMPORTANCE OF ADSORPTION WATER IN THE UPPER MARTIAN SURFACE.
D.T.F. Möhlmann, DLR Institut für Planetenforschung, Rutherfordstr.2, D-12489 Berlin, Germany,
dirk.moehlmann@dlr.de Lunar and Planetary Science XXXVI (2005)

"Where chemistry works, biochemical
processes can be expected to become
possible too. An example: The Photo-Fenton
reaction reduces ferric iron to ferrous iron in
the presence of UV and adsorption water.
Bacteria exist in terrestrial permafrost,
which are, in the presence of photons (VIS),
CO2 and water, able to oxidize ferrous iron
into ferric iron [8]. VIS-photons are used
under anaerobic conditions for fixation of
CO2 to organic carbon (CH2O)n. Energy,
necessary for life processes, can be derived
from this oxidation process."

[8] Ehrenreich A and F Widdell (1994) Appl. and
Environm. Microbiology, Vol. 60, No. 12, 4517-4526