There could be one hundred billion Earth-like planets in our galaxy, a US conference has heard.
So far, telescopes have been able to detect just over 300 planets outside our Solar System.
Very few of these would be capable of supporting life, however. Most are gas giants like our Jupiter, and many orbit so close to their parent stars that any microbes would have to survive roasting temperatures.
So where are these 'billons of earths'? No one knows because they haven't found any yet. They are basing their hypothesis on conjecture nothing more.