Agreed, Gary. Since it is 99% likely that MSL would be sent to Meridiani, the upshot is that including a likely slip from 2009 to 2011, by 2015 we will only know about 1 more spot on Mars than we do know (the north polar terrain, from Phoenix). We may then have a good sense of whether there was life or not at Meridiani (or we may just have some wreckage to photograph), but still have left a lot of holes in the global picture.

Better to delay MSL to 2015 or 2017, and visit 4 or 6 more spots in the interim. Maybe we'll find someplace more interesting even than Meridiani, and if not, at least we'll be more certain that it is the best candidate. Moreover, better to get more of the big picture, and not as Nick puts it, jump straight to "Were there sulfur-metabolizing life forms at Meridiani in the past?".

That being said, what should be the targets for MER clones? There's the original MER target sites, but, if we're sending half a dozen, we could probably accept more risk and take some more interesting but more dangerous sites too.

Suggestions?

The Melas sites would be interesting, as would the very young-looking lava flows and floods of Cerebus/Athabasca (though of course MER doesn't have the right instruments to tell *how* young, which would be the big question). Is the Holden Delta too rugged to even try an MER clone?