As for where much of the trace surface water on Mars might have come from, see my favorite dark-horse theory:
http://smallcomets.physics.uiowa.edu/ For an excellent account of a seemingly marginal hypothesis running the peer-review gauntlet to grudging acceptance, even if it takes well over a decade of persistence, see Louis Frank's Small Comets and Their Origins: The Ecstasy and Agony of the Scientific Debate. http://smallcomets.physics.uiowa.edu/lecture/ Hoffman should be so lucky. Not that Louis Frank has been all that lucky: post-grudging-acceptance, further investigation of this potential space resource seems to be going largely unfunded. (Or maybe I've got this wrong - maybe the anti-small-comet crowd declared a truce, and retreated, and the much smaller pro-small-comet crowd declared victory and retreated. Inquiring minds would like to know.) The relevance of this debate for Europa science planning? Huge, to my mind. We're being told that Mars almost certainly had lakes, rivers, maybe even oceans of water, when the case may be far from closed, and may end up being reopened at an embarrassing moment when lots of money has been thrown at the hypothesis as if it were axiomatic. In the meantime, there's a planet in our solar system that is thoroughly covered in frozen water, and behaves in a way that suggests a salty ocean underneath. Those seas, if they exist, may have thermal vents on their floors and a chemical mix conducive to initial or (argument from panspermia) further evolution of life. Or Europa water may be prohibitively toxic, we don't really know yet. If it exists, it may not be the only ocean in orbit around Jupiter. So I think this discussion stems less from my (admitted) gadfly tendencies, and more from trying to keep our priorities straight. Mars exploration should continue, don't get me wrong. But if the overarching question is whether there is another planet with life in the solar system, Europa still seems to me to be what Donald Rumsfeld might call a target-rich zone. ;-) -michael turner [EMAIL PROTECTED] == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
