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EVER get that sense of déjà vu? The American space agency NASA doesn’t seem to, but for everyone else there was a strangely familiar ring to the announcement last week of the discovery of water on Mars. For those with short memories, NASA trailed the gist of the finding earlier this year. It made a similar announcement in June 2000, when the Mars Global Surveyor spacecraft spotted evidence suggesting vast areas of the planet had once been heavily flooded. And even that wasn’t new. In the 1970s, the Viking spacecraft beamed back images of dry river beds, pointing to a wetter Martian past. So what’s going…