One of science’s greatest false alarms occurred on Aug. 7, 1996, when NASA announced that scientists had discovered “strong circumstantial evidence that life once existed on Mars.” That evidence was a scattering of tiny tube-like structures that looked for all the world like fossilized bacteria inside a small meteorite from Mars . Television networks interrupted regular broadcasts to cover the news , and President Clinton convened a Rose Garden press conference to comment on it. The rock, Clinton said , “speaks to us across … billions of years and millions of miles. It speaks of the possibility of life . If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered.” Alas, it was not confirmed. Further experiments showed that the same tiny formations can be the result of geologic—completely abiotic—processes.…