 If the fraction of stars with potentially habitable planets ( η ⊕ , " eta @-@ Earth " ) is on the order of a few tens of percent as Vogt proposes , and the Sun 's stellar neighborhood is a typical sample of the galaxy , then the discovery of Gliese 581 g in the habitable zone of its star points to the potential of billions of Earth @-@ like planets in our Milky Way galaxy alone . 
