In the 1960s, intent on demonstrating the superiority of our military-industrial complex to the Soviet Union, we funded the space program to reach the moon. In the 1970s and 1980s, we began to justify space expenditures by touting Teflon pans, super metal alloys, and miniaturized ro-botics. Now a new rationale for planetary exploration has emerged-environmentalism. The more we know about other worlds, say space enthusiasts, the better we can tackle the environmental dilemmas that beset our own planet.

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