IMPOSSIBLE? DON’T BE SO SURE! As the “realm of the possible” expands at an almost frightening rate, the tales of the best science fiction writers become more than merely imagination inspired. Voyaging to the stars, discovering life forms there which seem, at first, inconceivable to us oxygen-breathers, may well occur in this or not-too-distant generations. What might those intrepid explorers of the solar system and beyond encounter? Here are the speculations, some terrifying, some delightful, all thought-provoking, by science fiction’s greatest writers.