From Christensen himself:

"Dust coatings on rocks on the surface of Mars complicate and, if sufficiently thick, mask detection of the mineralogical signatures of rocks from martian orbit by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES). If the dust coatings are sufficiently thick, it is not possible to obtain mineralogical information about the rock substrate."

http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1899.pdf

Christensen's big announcemnt of hematite deposits on Mars now comes into question. Because hematite requires water, is he now saying this discovery is invalid?

Read:

http://www.lpi.usra.edu/meetings/martianhighlands2001/pdf/4025.pdf

"As a result, a lack of detections in TES,
THEMIS, and Mini-TES data must be approached with
caution when using the result as an input to geologic
and climatic studies."

Some major questions about TES need answers. Does Christensen support a wet hematite Mars? Or a dry "no limestone" Mars? Or is this more of an indication taht TES is not a very accurate instrument when trying to determine what is under a dust coated Mars?

BD