Curiosity found evidence that it had landed on an ancient riverbed, and it identified some interesting chemical species involving chlorine, sulphur, water and organic compounds, but nothing that could be construed as clear-cut evidence for life on Mars, past or present.
All of this underscores Carl Sagan’s caution, reiterated in his final book Billions and Billions, that extraordinary claims require extraordinary evidence.
And even if one day NASA does find such evidence, this would only raise the question as to whether we are all Martians, since (as we shall discuss below) life on Earth may have originated on Mars.
Search history
The current search for life on Mars is the latest of a series of observations (and controversies) extending back to the 1970s. In 1976 NASA’s...
