Carl Sagan:  There are some hundred billion galaxies , each with , on the average , a hundred billion stars , 1011 x 1011 = _ 1022 _ , ten billion trillion . In the face of such overpowering numbers , what is the likelihood that only one ordinary star , the Sun , is accompanied by an inhabited planet ? Why should we , tucked away in some forgotten corner of the Cosmos , be so fortunate ? To me , it seems far more likely that the universe is brimming over with life . But we humans do not yet know . We are just beginning our explorations . From eight billion light - years away we are hard pressed to find even the cluster in which our Milky Way Galaxy is embedded , much less the Sun or the Earth . The only planet we are sure is inhabited is a tiny speck of rock and metal , shining feebly by reflected sunlight , and at this distance utterly lost .