Whoops. Over the past four decades, NASA has launched a long series of exploratory probes to distant worlds in our solar system. It has sent up the Kepler space telescope to search for planets around other stars. All these missions have nurtured a hope, however faint, that astronomers might one day see unambiguous signs for life elsewhere in the universe. So it is only with the deepest sense of irony that one can hear the recent news that 36 years ago, scientists might have seen but disregarded proof of life on our closest planetary neighbor, Mars.
Don’t judge the experts too harshly, however. The problem of how to recognize alien life — life that might be radically unlike anything ever seen on Earth even at the molecular level — has been tormenting would-be exobiologists since the early days of space exploration.
What may be most surprising, though, is that this is not just a problem facing space scientists. Some biologists suspect that we may be overlooking alien types of life right here on Earth, too, even though they may be in fairly plain sight.
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