1. Is it true that Crystalline Hematite only forms in H2O?
2. Could these deposites have been formed under ground then thrust to
the surface?
3. Could these deposites been brought to Mars by meteorite/astroid
activity?
4. Could the Mars Global Surveyor been wrong about the discovery of
these deposites.

1: Crystalline hematite generally requires H2O to form, but it is not the only way. There are about 5 theorised ways in which hematite found on mars may have formed and most of these involve liquid water. The only one that does not, involves thermal oxidation of magnatite rich lava. However from the photographs we have of these regions there is little to suggest lava flows and volcanic deposites, rather the isolated areas where grey hematite has been found are within sedimentary deposites and most within a closed basin, suggesting chemical precipitation from standing bodies of aqueous fluids.

2: The different mechanisms for the formation of grey hematite, as outlined by Christensen are:
a: low temperature precipitation of Iron oxides/hydroxides from a standing body of oxygenated, iron rich water and subsequent alteration to grey hematite.
b: low temperature leaching of iron bearing materials leaving a residual that then alters to grey hematite.
c: direct precipitation of grey hematite from iron rich fluids of a hydrothermal origin (underwater volcanic vent and associated circulating fluids).
d: the formation of a grey hematite surface coating during weathering,
and as mentioned before
e: thermal oxidation of magnitite rich lava.
Some of these formation processes allow for hematite to be formed in under ground.

3: Given the nature of these deposites, it is very unlikely that they were brought to Mars by an asteroid or meteorite.

4: Both TES (Mars Global Surveyor) and THEMIS (Mars Odyssey) have picked up the spectral signatures of these deposites, so it is unlikely to be an incorrect discovery.

Given the current interest in attempting to determine if Mars was warm and wet in the past, the hematite deposites are high contenders for unmanned landing sites. So keep your eyes open in the next few years for the results.

Sarah Chamberlain
Australian Centre for Astrobiology