How Long Until We Find a Second Earth?

How Long Until We Find a Second Earth?: "Gliese 876 is a modest star, just one-third the mass of our sun and only 15 light-years away, but it has a history-making planetary system all its own. In 1998 a team led by Geoff Marcy of the University of California at Berkeley detected the first sign of something interesting there: a giant planet, twice the mass of Jupiter, circling Gliese 876 once every two months, its gravity yanking the star back and forth at the speed of a jet plane. Three years later the same group found a second planet, half the mass of Jupiter and closer in, pulling the star around at the speed of a race car. Although the planets are too faint to be seen directly, their motions cause the star’s spectrum to wobble back and forth across the digital detector of an astronomical telescope."