Nick Hoffman wrote:
My personal favourite remains the Athabasca Valles...

Alex writes:
Athabasca Valles is, as Nick is aware from our discussions elsewhere, a very attractive site (evidence of "fresh" flows) that is favored by many, most notably the University of Arizona team headed by Alfred McEwen.

That said, unfortunately, our two favorite sites run afoul of each other. There is an engineering constraint that the landing sites for MER-A and MER-B have to be separated by 37 degrees of surface arc or more, thereby eliminating the possibility that both Gusev Crater and Athabasca Valles can be simultaneously targeted by both rovers on the MER 2003 mission.

For those who are interested, the engineering constraint refers to communications. The Deep Space Network (DSN) does have the capability to support "multiple spacecraft per aperture" mode, which permits the
same antenna to track multiple spacecraft, provided they fall within a
particular antenna's beam pattern. However, the >= 37 degree surface
separation arc operational constraint for the 2003 MERs refers to the orbital relay pipeline. Primarily, the separation ensures adequate UHF return through the 2001 Mars Odyssey relay (primary) and Mars Global Surveyor's Mars Relay (MR), which is the backup, by avoiding a situation where MER-A and MER-B see the same orbiter at the same time. There are other minor operational and communications considerations that
contribute, to varying degrees, to this constraint as well.

Alex R. Blackwell
University of Hawaii