Gary wrote:
What in your opinion would be the mechanism for producing hematite on Mars? Is a non-aqueous process for hematite production possible? Can hematite percipitate out of liquid water if there is no free oxygen present?

Alex writes:

If you are not aware of the following, then you may wish to see

Allen, Carlton C.; Frances Westall; Rachel T. Schelble
Importance of a Martian Hematite Site for Astrobiology, Astrobiology 1, 111 (2001).

Which is available as a free download at:
http://ernesto.catchword.com/vl=67828973/cl=35/nw=1/rpsv/catchword/mal/15311074/v1n1/s8/p111

Gary wrote:
Why is Gusev still being considered [for MER 2003]?

Alex writes:
Nathalie Cabrol et al.'s presentation (~10 Mb PowerPoint) covering the rationale behind Gusev Crater from the recent 2003 MER Landing Site Selection Workshop:

Crater Lakes I: Gusev, Boedicker, and "Unnamed" EP69A
Nathalie Cabrol, Science Spokesperson

is available at
http://marsoweb.nas.nasa.gov/landingsites/mer2003/doc/pasadena_01/talks/Cabrol-MER.ppt

Frankly, I prefer the site for other (non-exobiology) reasons. Gusev Crater/Ma'adim Vallis is an interesting geological target in its own right (personally I favor it as a target), but IMO satisfying all of the various disciplines probably requires a landing
closer to the SE corner (near the junction with Ma'adim) rather than the central portion of the crater as was the case with the early ellipse(s). Based on the engineering constraints for MER-A (i.e., 15 degrees S latitude limit) Gusev will be a stretch as the ellipse is just at the edge of the envelope.

As you noted, MOC NA imagery has cast a bit of doubt on *accessibility* to the putative lacustrine deposits,

For example, see

Edgett, K.S., and M.C. Malin, MGS MOC and water on Mars: No northern plains ocean, no Gusev Crater lake sediment access, Fall Meeting of the American Geophysical Union, San Francisco, December 2000.

an excerpt of which I post below:

"Intracrater lake hypotheses have focused on Gusev Crater, which is connected to the Ma'adim valley. Gusev has received considerable attention as a possible landing site to serve the interests of the Mars astrobiology community. MOC images show that there is no access at the surface to the types of materials of which astrobiologists dream (e.g., sedimentary rock outcrops, salt pans, tufa towers). Gusev's floor and walls are highly modified and mantled; and while small impact craters may sample the subsurface, such materials are also mantled and their provenance is problematic. Other impact basins, however, do show tantalizing evidence of access to layered sediment (whether subaerial or sublacustrine is unknown); of particular interest is Holden Crater, connected to Uzboi Vallis, which exhibits outcrops of alternating light- and dark-toned bands. Unfortunately, such locations are inaccessible to presently-conceived lander/rover missions which are dictated by engineering constraints rather than science objectives. New MGS MOC images are received every day, and analysis is on-going."

not whether Gusev ever contained a closed body of water, something that most Mars scientists agree was the case. At any rate, the "newer" ellipse still targets the terrain west of Thyra and appears to be only a minor "tweak" of the one proposed by Cabrol et al. at the recent Pasadena workshop

Alex R. Blackwell
University of Hawaii