If all goes according to plan, the arrival of NASA's Perseverance rover on February 18, 2021, will mark the end of an era in Mars exploration.
The first era began in 1964 when Mariner 4, the first successful Mars spacecraft, flew by the planet and sent back images of a seemingly barren, cratered, Moonlike world. To a public raised on fanciful tales of Mars as harsh but habitable land, the views came as a shock. Subsequent missions painted a more varied, nuanced portrait of the Martian environment, raising hopes for the 1976 Viking missions. Two landers dug into the red soil and tested it for signs of life — but they came up empty. Those results closed out Era One with a disappointing message: Mars is a dead planet.
Over the next two decades, planetary scientists began to realize that the Viking experiments were naive, based on insufficient knowledge about ...
