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If solar mixing does occur, it would also affect other planets of the solar system. In Nature, Carl Sagan of Cornell and Andrew Young of Caltech have suggested that fluctuating solar output could explain such Martian mysteries as the river-bed-like channels recently photographed by the Mariner 9 spacecraft. Martian water, now locked firmly in the frozen poles, presumably would have flowed freely during warmer times. Sagan and Young go further. Suspecting that our sun is not unique in its quirky behavior, they checked other nearby stars. In the cluster Praesepe, they found a number of stars that varied widely from expected energy output. Such variations, they say, broaden the long-term temperature ranges to be expected near these stars, increasing the chances that earthlike climatesand perhaps lifeexist.