|Artist's conception of Kepler-10b, NASA|
The presumption that there are millions of Earth-like planets in habitable zones is based on theory that is not supported by evidence. This point has recently been made by Howard Smith, a senior astrophysicist at Harvard. He has made the claim that "we are alone in the universe" after an analysis of the 500 planets discovered so far showed all were hostile to life.never mind rare Earths, there aren’t any spare Earths, period. Better take care of the one we got.
"Dr Smith said the extreme conditions found so far on planets discovered outside out Solar System are likely to be the norm, and that the hospitable conditions on Earth could be unique.
"We have found that most other planets and solar systems are wildly different from our own. They are very hostile to life as we know it," he said."