There appears to be something like an aquifer beneath the surface of Mars. Ice found on the floor of at least two craters so far (Phoenix lander). As to the polar caps, they are a mixture of water ice and frozen carbon dioxide ("dry ice"), proportions still up for speculation and being analysed (fairly detailed article, Astronomy magazine, September 16, 2009).

The question, once again, is "in usable quantities?"

Looks promising, but I wouldn't send out colonists for a few weeks yet. . . .

(Unless I could nominate who they should be.)

Don Firth

P. S. Some years back, an old drinking buddy from the early 1960s named Jerry Pournelle (I didn't even know he was interested in writing science fiction at the time, but I did know that he had a wall full of degrees in various physical sciences) became a science advisor to Pres. Reagan. He worked out a weapons system for "Star Wars" (SDI, not the movies) that consisted of dropping heavy metal rods from orbit. Hit like a meteor strike, no explosives necessary. Do some real damage to bunkers, underground facilities, etc.

Can't remember now what he called it, but you might be able to google something about it.